J ² = 1

Hi Ole,

> On 21 Nov 2018, at 15:55, [email protected] [EVGRAY] <[email protected]> wrote:
> 
> I just looked at one of Rosemary Ainslie's patent applications (https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=WO&NR=03007657A2&KC=A2&FT=D&ND=3&date=20030123&DB=&locale=en_EP# <https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=WO&amp;NR=03007657A2&amp;KC=A2&amp;FT=D&amp;ND=3&amp;date=20030123&amp;DB=&amp;locale=en_EP#>).
> This is a very basic switcher that has nothing to catch the flyback energy except for the avalanche breakdown of the switch. This is a very stressful way of using a transistor which is normally avoided.
> 
> 
> Figure 2 of the above referred patent.
> 
> Normally when an avalanche (secondary breakdown) happens in a transistor it cannot shut off by itself and thus ends its life in smoke or in an explosion if the current isn't shut off externally.
> 
> The MOSFET Andreas mentioned (IRFPG50s <https://www.vishay.com/docs/91254/91254.pdf>) is repetitive avalanche rated and as such can withstand avalanches to some degree without destruction after the first electron avalanche through it.
> 
> Here is a document about avalanche in MOSFETs (Application Note AN-1005): https://www.vishay.com/docs/90160/an1005.pdf <https://www.vishay.com/docs/90160/an1005.pdf>.
> 

The missing snubber in the patent drawing can mean two things. Either, it was omitted (considered an important detail for a patent application), or it was intentionally left out. We usually describe an inductor with

	UL = L dI/dt

but all know that this might not be the complete story. There very well  might also be an extra term 

	… + k d^2I/dt^2 

with k being so small that it can normally be neglected. But for very steep and accelerated current rises it might be significant. Could this cause an extra voltage spike so high that some current is flowing back into the power supply while energising the inductor? Hector suggested a xenon flash to band a coil. Why? Bacause it switches on much faster than a semiconductor. May be Ainslie intentionally or not even consciously drives the MOSFET into avalanche to get a very steep current rise that exhibits an usually overseen effect in the inductor!?

If so, let’s look a bit close to her circuit. The gate gets a potential to switch the MOSFET on (usual stuff). The gate signal is then dropped down to switch off. The fly-back spike has nowhere to got (thus pretty high potential) and drives the MOSFET into availing which causes it to switch on/off very quickly due to the very fast avalanches which triggers the usually overseen inductive effect described above. Does this make any sense. Can we really use avalanche rated MOSFETs for such endeavours or will they die pretty quickly? Should we rather look into xenon flashers to get the same effect but more reliably?

Regards,

 Andreas

AndreasDo you know anybody having a working Hector zenon flasher circuit, that might be willing to coach an interested replicator through the technique?
I have two of his recommended zenon boards that are fired by 12 volts. What have people achieved, and what do I have to do to replicate those results?Cheers Warren
Sent from Yahoo Mail on Android 
 
  On Thu, 22 Nov 2018 at 5:06 AM, An Hö [email protected] [EVGRAY]<[email protected]> wrote:       
Hi Ole,


On 21 Nov 2018, at 15:55, [email protected] [EVGRAY] <[email protected]> wrote:

I just looked at one of Rosemary Ainslie's patent applications (https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=WO&NR=03007657A2&KC=A2&FT=D&ND=3&date=20030123&DB=&locale=en_EP#).
This is a very basic switcher that has nothing to catch the flyback energy except for the avalanche breakdown of the switch. This is a very stressful way of using a transistor which is normally avoided.


Figure 2 of the above referred patent.

Normally when an avalanche (secondary breakdown) happens in a transistor it cannot shut off by itself and thus ends its life in smoke or in an explosion if the current isn't shut off externally.

The MOSFET Andreas mentioned (IRFPG50s) is repetitive avalanche rated and as such can withstand avalanches to some degree without destruction after the first electron avalanche through it.



Here is a document about avalanche in MOSFETs (Application Note AN-1005): https://www.vishay.com/docs/90160/an1005.pdf.



The missing snubber in the patent drawing can mean two things. Either, it was omitted (considered an important detail for a patent application), or it was intentionally left out. We usually describe an inductor with
 UL = L dI/dt
but all know that this might not be the complete story. There very well  might also be an extra term 
 … + k d^2I/dt^2 
with k being so small that it can normally be neglected. But for very steep and accelerated current rises it might be significant. Could this cause an extra voltage spike so high that some current is flowing back into the power supply while energising the inductor? Hector suggested a xenon flash to band a coil. Why? Bacause it switches on much faster than a semiconductor. May be Ainslie intentionally or not even consciously drives the MOSFET into avalanche to get a very steep current rise that exhibits an usually overseen effect in the inductor!?
If so, let’s look a bit close to her circuit. The gate gets a potential to switch the MOSFET on (usual stuff). The gate signal is then dropped down to switch off. The fly-back spike has nowhere to got (thus pretty high potential) and drives the MOSFET into availing which causes it to switch on/off very quickly due to the very fast avalanches which triggers the usually overseen inductive effect described above. Does this make any sense. Can we really use avalanche rated MOSFETs for such endeavours or will they die pretty quickly? Should we rather look into xenon flashers to get the same effect but more reliably?
Regards,
 Andreas

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Hi Andreas,

I don't know which one of xenon tube or avalanche switching a power MOSFET will last the longest. Both types of phenomenon happen very fast. One is a flash over through a gas while the other is a flash over through a semiconductor crystal. Some of the other figures of the patent application have the load across the inductor. When in parallel the load can be adapted to limit the flyback voltage to below the breakdown voltage of the MOSFET switch. It is also mentioned that it wasn't known which way works the best. The measurements mentioned in the patent application shows up to twice the input power being output in the resistor.

More information or experimentation is needed for any conclusion. Questions like does the MOSFET switch have to go into the breakdown region? Or are the readings valid?  It is mentioned that the load resistor has a hollow core. If it's an inductive resistor it has inductance. If having inductance some of the power must be reactive power stored as a magnetic field in the inductive resistor. If this is the case the measurements aren't valid! A calorimeter measurement would settle this. Else a non-inductive load will have to be used for determining the output power. This can be done by splitting up the inductive part and the resistive part of the load by using more idealized components and then measuring on the more ideal components. Alternatively an oscilloscope with mathematical functions rigged up as a power meter will show the active and reactive parts of the power. Or a simple two channel scope will be able to show the phase relationship between the current and voltage. The curves have to be scaled copies of each other for pure active power. It not there is also reactive power.

Regards
Ole




 

---In [email protected], <freeen2012@...> wrote :

 Hi Ole, 
 On 21 Nov 2018, at 15:55, onielsen@... mailto:onielsen@... [EVGRAY] <[email protected] mailto:[email protected]> wrote:

 I just looked at one of Rosemary Ainslie's patent applications (https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=WO&NR=03007657A2&KC=A2&FT=D&ND=3&date=20030123&DB=&locale=en_EP# https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=WO&amp;NR=03007657A2&amp;KC=A2&amp;FT=D&amp;ND=3&amp;date=20030123&amp;DB=&amp;locale=en_EP#).
This is a very basic switcher that has nothing to catch the flyback energy except for the avalanche breakdown of the switch. This is a very stressful way of using a transistor which is normally avoided.


Figure 2 of the above referred patent.

Normally when an avalanche (secondary breakdown) happens in a transistor it cannot shut off by itself and thus ends its life in smoke or in an explosion if the current isn't shut off externally.

The MOSFET Andreas mentioned (IRFPG50s https://www.vishay.com/docs/91254/91254.pdf) is repetitive avalanche rated and as such can withstand avalanches to some degree without destruction after the first electron avalanche through it.

 Here is a document about avalanche in MOSFETs (Application Note AN-1005): https://www.vishay.com/docs/90160/an1005.pdf https://www.vishay.com/docs/90160/an1005.pdf.


 


The missing snubber in the patent drawing can mean two things. Either, it was omitted (considered an important detail for a patent application), or it was intentionally left out. We usually describe an inductor with
 

 UL = L dI/dt
 

 but all know that this might not be the complete story. There very well  might also be an extra term 
 

 … + k d^2I/dt^2 
 

 with k being so small that it can normally be neglected. But for very steep and accelerated current rises it might be significant. Could this cause an extra voltage spike so high that some current is flowing back into the power supply while energising the inductor? Hector suggested a xenon flash to band a coil. Why? Bacause it switches on much faster than a semiconductor. May be Ainslie intentionally or not even consciously drives the MOSFET into avalanche to get a very steep current rise that exhibits an usually overseen effect in the inductor!?
 

 If so, let’s look a bit close to her circuit. The gate gets a potential to switch the MOSFET on (usual stuff). The gate signal is then dropped down to switch off. The fly-back spike has nowhere to got (thus pretty high potential) and drives the MOSFET into availing which causes it to switch on/off very quickly due to the very fast avalanches which triggers the usually overseen inductive effect described above. Does this make any sense. Can we really use avalanche rated MOSFETs for such endeavours or will they die pretty quickly? Should we rather look into xenon flashers to get the same effect but more reliably?
 

 Regards,
 

  Andreas

I bought a tube of Rosemary's mosfets that she is using with success in her experiments.Of course, I am am more interested in a practical, reliable system.Even a flakey method that depends on deviant aspects of a mosfet will energize a manufacturer to shape up, and produce what might be marketing magic. The Chinese are very good at giving customers what they want. Funny enough, Texas Instruments will do prototype manufacturing as well, and seem easy and friendly to work with. I also used a custom manufacturer in Buffalo, that was very helpful for the deadmau5 spherical video head I made. About 15% of prototypes are rejects, and you have to test each one yourself, after recieving them from the manufacturer.So with that in mind, let us not be pessimistic regarding producing a component that might have unexpected defects, that have a use, never considered of being the main feature for choosing it.Cheers Warren

Sent from Yahoo Mail on Android 
 
  On Thu, 22 Nov 2018 at 5:06 AM, An Hö [email protected] [EVGRAY]<[email protected]> wrote:       
Hi Ole,


On 21 Nov 2018, at 15:55, [email protected] [EVGRAY] <[email protected]> wrote:

I just looked at one of Rosemary Ainslie's patent applications (https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=WO&NR=03007657A2&KC=A2&FT=D&ND=3&date=20030123&DB=&locale=en_EP#).
This is a very basic switcher that has nothing to catch the flyback energy except for the avalanche breakdown of the switch. This is a very stressful way of using a transistor which is normally avoided.


Figure 2 of the above referred patent.

Normally when an avalanche (secondary breakdown) happens in a transistor it cannot shut off by itself and thus ends its life in smoke or in an explosion if the current isn't shut off externally.

The MOSFET Andreas mentioned (IRFPG50s) is repetitive avalanche rated and as such can withstand avalanches to some degree without destruction after the first electron avalanche through it.



Here is a document about avalanche in MOSFETs (Application Note AN-1005): https://www.vishay.com/docs/90160/an1005.pdf.



The missing snubber in the patent drawing can mean two things. Either, it was omitted (considered an important detail for a patent application), or it was intentionally left out. We usually describe an inductor with
 UL = L dI/dt
but all know that this might not be the complete story. There very well  might also be an extra term 
 … + k d^2I/dt^2 
with k being so small that it can normally be neglected. But for very steep and accelerated current rises it might be significant. Could this cause an extra voltage spike so high that some current is flowing back into the power supply while energising the inductor? Hector suggested a xenon flash to band a coil. Why? Bacause it switches on much faster than a semiconductor. May be Ainslie intentionally or not even consciously drives the MOSFET into avalanche to get a very steep current rise that exhibits an usually overseen effect in the inductor!?
If so, let’s look a bit close to her circuit. The gate gets a potential to switch the MOSFET on (usual stuff). The gate signal is then dropped down to switch off. The fly-back spike has nowhere to got (thus pretty high potential) and drives the MOSFET into availing which causes it to switch on/off very quickly due to the very fast avalanches which triggers the usually overseen inductive effect described above. Does this make any sense. Can we really use avalanche rated MOSFETs for such endeavours or will they die pretty quickly? Should we rather look into xenon flashers to get the same effect but more reliably?
Regards,
 Andreas

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OlePutting the resistor in mineral oil, perhaps in a test tube, inside of a sleave of pipe insulating foam, 
might be a possible apparatus?Of course, a temperature sensor, as well.The mineral oil solution is good for circuit boards that tend to have hot spots, that just by keeping them cool, will keep functioning, until you can perhaps address the engineering problems.Cheers Warren
Sent from Yahoo Mail on Android 
 
  On Thu, 22 Nov 2018 at 9:34 AM, [email protected] [EVGRAY]<[email protected]> wrote:       
Hi Andreas,

I don't know which one of xenon tube or avalanche switching a power MOSFET will last the longest. Both types of phenomenon happen very fast. One is a flash over through a gas while the other is a flash over through a semiconductor crystal. Some of the other figures of the patent application have the load across the inductor. When in parallel the load can be adapted to limit the flyback voltage to below the breakdown voltage of the MOSFET switch. It is also mentioned that it wasn't known which way works the best. The measurements mentioned in the patent application shows up to twice the input power being output in the resistor.

More information or experimentation is needed for any conclusion. Questions like does the MOSFET switch have to go into the breakdown region? Or are the readings valid?  It is mentioned that the load resistor has a hollow core. If it's an inductive resistor it has inductance. If having inductance some of the power must be reactive power stored as a magnetic field in the inductive resistor. If this is the case the measurements aren't valid! A calorimeter measurement would settle this. Else a non-inductive load will have to be used for determining the output power. This can be done by splitting up the inductive part and the resistive part of the load by using more idealized components and then measuring on the more ideal components. Alternatively an oscilloscope with mathematical functions rigged up as a power meter will show the active and reactive parts of the power. Or a simple two channel scope will be able to show the phase relationship between the current and voltage. The curves have to be scaled copies of each other for pure active power. It not there is also reactive power.

Regards
Ole







---In [email protected], <freeen2012@...> wrote :

Hi Ole,


On 21 Nov 2018, at 15:55, onielsen@... [EVGRAY] <[email protected]> wrote:

I just looked at one of Rosemary Ainslie's patent applications (https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=WO&NR=03007657A2&KC=A2&FT=D&ND=3&date=20030123&DB=&locale=en_EP#).
This is a very basic switcher that has nothing to catch the flyback energy except for the avalanche breakdown of the switch. This is a very stressful way of using a transistor which is normally avoided.


Figure 2 of the above referred patent.

Normally when an avalanche (secondary breakdown) happens in a transistor it cannot shut off by itself and thus ends its life in smoke or in an explosion if the current isn't shut off externally.

The MOSFET Andreas mentioned (IRFPG50s) is repetitive avalanche rated and as such can withstand avalanches to some degree without destruction after the first electron avalanche through it.



Here is a document about avalanche in MOSFETs (Application Note AN-1005): https://www.vishay.com/docs/90160/an1005.pdf.




The missing snubber in the patent drawing can mean two things. Either, it was omitted (considered an important detail for a patent application), or it was intentionally left out. We usually describe an inductor with
 UL = L dI/dt
but all know that this might not be the complete story. There very well  might also be an extra term 
 … + k d^2I/dt^2 
with k being so small that it can normally be neglected. But for very steep and accelerated current rises it might be significant. Could this cause an extra voltage spike so high that some current is flowing back into the power supply while energising the inductor? Hector suggested a xenon flash to band a coil. Why? Bacause it switches on much faster than a semiconductor. May be Ainslie intentionally or not even consciously drives the MOSFET into avalanche to get a very steep current rise that exhibits an usually overseen effect in the inductor!?
If so, let’s look a bit close to her circuit. The gate gets a potential to switch the MOSFET on (usual stuff). The gate signal is then dropped down to switch off. The fly-back spike has nowhere to got (thus pretty high potential) and drives the MOSFET into availing which causes it to switch on/off very quickly due to the very fast avalanches which triggers the usually overseen inductive effect described above. Does this make any sense. Can we really use avalanche rated MOSFETs for such endeavours or will they die pretty quickly? Should we rather look into xenon flashers to get the same effect but more reliably?
Regards,
 Andreas

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Hi Warren,

A thermos bottle (aka Dewar flask or vacuum bottle) with water will do. If knowing the initial temperature and the end temperature of the water it is possible to calculate the amount of heat energy been added.

Having the scope I find it easier to do a direct measurement of the electrical power or even energy by integrating the power over time if the scope has enough memory depth for that.

Regards
Ole
 

---In [email protected], <schoonersolsticemoon@...> wrote :

 Ole Putting the resistor in mineral oil, perhaps in a test tube, inside of a sleave of pipe insulating foam, 
might be a possible apparatus?
 Of course, a temperature sensor, as well.
 The mineral oil solution is good for circuit boards that tend to have hot spots, that just by keeping them cool, will keep functioning, until you can perhaps address the engineering problems.
 Cheers Warren
 Sent from Yahoo Mail on Android https://go.onelink.me/107872968?pid=InProduct&c=Global_Internal_YGrowth_AndroidEmailSig__AndroidUsers&af_wl=ym&af_sub1=Internal&af_sub2=Global_YGrowth&af_sub3=EmailSignature
 
 On Thu, 22 Nov 2018 at 9:34 AM, onielsen@... [EVGRAY]
 <[email protected]> wrote:

   Hi Andreas,

I don't know which one of xenon tube or avalanche switching a power MOSFET will last the longest. Both types of phenomenon happen very fast. One is a flash over through a gas while the other is a flash over through a semiconductor crystal. Some of the other figures of the patent application have the load across the inductor. When in parallel the load can be adapted to limit the flyback voltage to below the breakdown voltage of the MOSFET switch. It is also mentioned that it wasn't known which way works the best. The measurements mentioned in the patent application shows up to twice the input power being output in the resistor.

More information or experimentation is needed for any conclusion. Questions like does the MOSFET switch have to go into the breakdown region? Or are the readings valid?  It is mentioned that the load resistor has a hollow core. If it's an inductive resistor it has inductance. If having inductance some of the power must be reactive power stored as a magnetic field in the inductive resistor. If this is the case the measurements aren't valid! A calorimeter measurement would settle this. Else a non-inductive load will have to be used for determining the output power. This can be done by splitting up the inductive part and the resistive part of the load by using more idealized components and then measuring on the more ideal components. Alternatively an oscilloscope with mathematical functions rigged up as a power meter will show the active and reactive parts of the power. Or a simple two channel scope will be able to show the phase relationship between the current and voltage. The curves have to be scaled copies of each other for pure active power. It not there is also reactive power.

Regards
Ole





 

---In [email protected], <freeen2012@...> wrote :

 Hi Ole, 
 On 21 Nov 2018, at 15:55, onielsen@... mailto:onielsen@... [EVGRAY] <[email protected] mailto:[email protected]> wrote:

 I just looked at one of Rosemary Ainslie's patent applications (https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=WO&NR=03007657A2&KC=A2&FT=D&ND=3&date=20030123&DB=&locale=en_EP# https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=WO&NR=03007657A2&KC=A2&FT=D&ND=3&date=20030123&DB=&locale=en_EP#).
This is a very basic switcher that has nothing to catch the flyback energy except for the avalanche breakdown of the switch. This is a very stressful way of using a transistor which is normally avoided.


Figure 2 of the above referred patent.

Normally when an avalanche (secondary breakdown) happens in a transistor it cannot shut off by itself and thus ends its life in smoke or in an explosion if the current isn't shut off externally.

The MOSFET Andreas mentioned (IRFPG50s https://www.vishay.com/docs/91254/91254.pdf) is repetitive avalanche rated and as such can withstand avalanches to some degree without destruction after the first electron avalanche through it.

 Here is a document about avalanche in MOSFETs (Application Note AN-1005): https://www.vishay.com/docs/90160/an1005.pdf https://www.vishay.com/docs/90160/an1005.pdf.


 


The missing snubber in the patent drawing can mean two things. Either, it was omitted (considered an important detail for a patent application), or it was intentionally left out. We usually describe an inductor with
 

 UL = L dI/dt
 

 but all know that this might not be the complete story. There very well  might also be an extra term 
 

 … + k d^2I/dt^2 
 

 with k being so small that it can normally be neglected. But for very steep and accelerated current rises it might be significant. Could this cause an extra voltage spike so high that some current is flowing back into the power supply while energising the inductor? Hector suggested a xenon flash to band a coil. Why? Bacause it switches on much faster than a semiconductor. May be Ainslie intentionally or not even consciously drives the MOSFET into avalanche to get a very steep current rise that exhibits an usually overseen effect in the inductor!?
 

 If so, let’s look a bit close to her circuit. The gate gets a potential to switch the MOSFET on (usual stuff). The gate signal is then dropped down to switch off. The fly-back spike has nowhere to got (thus pretty high potential) and drives the MOSFET into availing which causes it to switch on/off very quickly due to the very fast avalanches which triggers the usually overseen inductive effect described above. Does this make any sense. Can we really use avalanche rated MOSFETs for such endeavours or will they die pretty quickly? Should we rather look into xenon flashers to get the same effect but more reliably?
 

 Regards,
 

  Andreas

Image missing. Here it is again.

Hi Andreas,

Both ways can be used. For low inductance of a current shunt let the return wire go close to and in parallel with the shunt resistor to minimize any area for the magnetic field.

Here the return wire is twisted around the current shunt.

Also the 50 Ohm feed through is necessary. Without it a lot of reflections will happen unless the scope itself has a 50 Ohm input. As scope inputs usually are 1M Ohm the signal will be reflected due to the great impedance mismatch from 50m Ohm to 1M Ohm and the signal will drown in noise. 50m Ohm to 50 Ohm reduces the reflections a lot.

Regards
Ole

 

---In [email protected], <onielsen@...> wrote :

 Hi Andreas,

Both ways can be used. For low inductance of a current shunt let the return wire go close to and in parallel with the shunt resistor to minimize any area for the magnetic field.

Now the image is attached!

Regards
Ole
 

---In [email protected], <onielsen@...> wrote :

 Image missing. Here it is again.

Hi Andreas,

Both ways can be used. For low inductance of a current shunt let the return wire go close to and in parallel with the shunt resistor to minimize any area for the magnetic field.

Here the return wire is twisted around the current shunt.

Also the 50 Ohm feed through is necessary. Without it a lot of reflections will happen unless the scope itself has a 50 Ohm input. As scope inputs usually are 1M Ohm the signal will be reflected due to the great impedance mismatch from 50m Ohm to 1M Ohm and the signal will drown in noise. 50m Ohm to 50 Ohm reduces the reflections a lot.

Regards
Ole

 

---In [email protected], <onielsen@...> wrote :

 Hi Andreas,

Both ways can be used. For low inductance of a current shunt let the return wire go close to and in parallel with the shunt resistor to minimize any area for the magnetic field.

> On 22 Nov 2018, at 17:27, [email protected] [EVGRAY] <[email protected]> wrote:
> 
> Having the scope I find it easier to do a direct measurement of the electrical power or even energy by integrating the power over time if the scope has enough memory depth for that.

How do you measure the current precisely? Voltage over a shunt or with a current probe? I found it even difficult to find shunts with low enough inductivity. :-(

Andreas

Hi Andreas,

Yahoo doesn't like to transfer the complete messages today even though the delay isn't too great. I completed the message history from the picture and hope it gets through.

To make your own BNC feed through get one male and one female 50 Ohm connector and an inductance free 50 Ohm resistor. Then connect them all in parallel. Instead of one 50 Ohm resistor perhaps use two100 Ohm resistors in parallel. The resistors must be able to dissipate the power at the max voltage across them. With a low impedance current shunt this voltage won't be great. The 50 Ohm feed through must be placed as close as possible to the input of the scope's input amplifier which means the BNC input terminal of the scope.

For high speed oscilloscope probes the inner conductor of the coax cables are made of resistive wire to dissipate energy along the wire. This reduces reflections when the signal reaches the ends of the cable.

I know of a compensation device like used in oscilloscope probes (i.e. like 1:10, 1:20, 1:50, 1:100 etc.). But this device is for audio signals. He tells that when it's correct adjusted the sound picture has depth end everything placed correct. He got the idea from oscilloscope probes where you want to see the signal on the screen like how it is at the probe tip. Never mind how it looks along the signal path as long as the end result is correct. That's what the compensation is for. I.e. when the compensation is correct adjusted an input square wave looks like a square wave on the screen. Without the compensation the corners of the square wave are round. With too much compensation the corners becomes pin shaped.

Regards
Ole
 

---In [email protected], <freeen2012@...> wrote :

 Hi Ole, 
 On 22 Nov 2018, at 18:51, onielsen@... mailto:onielsen@... [EVGRAY] <[email protected] mailto:[email protected]> wrote:

 Both ways can be used. For low inductance of a current shunt let the return wire go close to and in parallel with the shunt resistor to minimize any area for the magnetic field.

Here the return wire is twisted around the current shunt.

Also the 50 Ohm feed through is necessary. Without it a lot of reflections will happen unless the scope itself has a 50 Ohm input. As scope inputs usually are 1M Ohm the signal w ill be reflected due to the great impedance mismatch from 50m Ohm to 1M Ohm and the signal will drown in noise. 50m Ohm to 50 Ohm reduces the reflections a lot.

 Thanks for the pic (illustrates it well). I already have such a 50 Ohm feed through but never really understood what exactly it does and therefore have never used it. I understand it has an impedance of 50 Ohm like the coax cable to prevent reflexions, yes, but how does it transfer the potential difference to be measured (over the shunt) to the 1M Ohm impedance input of the scope. If we had to build such a 50 Ohm feed through what would we have to do (what is it composed of)? This might help me to understand how it works. 
 
 Thanks a lot,
 

  Andreas

Hi Ole,

> On 22 Nov 2018, at 18:51, [email protected] [EVGRAY] <[email protected]> wrote:
> 
> Both ways can be used. For low inductance of a current shunt let the return wire go close to and in parallel with the shunt resistor to minimize any area for the magnetic field.
> 
> Here the return wire is twisted around the current shunt.
> 
> Also the 50 Ohm feed through is necessary. Without it a lot of reflections will happen unless the scope itself has a 50 Ohm input. As scope inputs usually are 1M Ohm the signal will be reflected due to the great impedance mismatch from 50m Ohm to 1M Ohm and the signal will drown in noise. 50m Ohm to 50 Ohm reduces the reflections a lot.

Thanks for the pic (illustrates it well). I already have such a 50 Ohm feed through but never really understood what exactly it does and therefore have never used it. I understand it has an impedance of 50 Ohm like the coax cable to prevent reflexions, yes, but how does it transfer the potential difference to be measured (over the shunt) to the 1M Ohm impedance input of the scope. If we had to build such a 50 Ohm feed through what would we have to do (what is it composed of)? This might help me to understand how it works. 

Thanks a lot,

 Andreas

Hi Ole,

Same concept we use when designing a zobel network for a transformer in
a mic preamp.  I suppose this magic device sits near the speaker.   I
have a hard time believing this would do much with most dynamic speakers
as the mechanical impedance and reactance makes a square wave hard to
recognize.  On an electrostatic speaker though one can see a pretty good
square wave however that is one huge capacitor compared to some trimmer
so likely would require a tunable inductor in line with the step up
transformer.  Of course I am referring to using a laboratory mic for
looking at the square wave not just a probe across the speaker terminals.


On 11/22/2018 11:29 AM, [email protected] [EVGRAY] wrote:
>  
>
> Hi Andreas,
>
> Yahoo doesn't like to transfer the complete messages today even though
> the delay isn't too great. I completed the message history from the
> picture and hope it gets through.
>
> To make your own BNC feed through get one male and one female 50 Ohm
> connector and an inductance free 50 Ohm resistor. Then connect them
> all in parallel. Instead of one 50 Ohm resistor perhaps use two100 Ohm
> resistors in parallel. The resistors must be able to dissipate the
> power at the max voltage across them. With a low impedance current
> shunt this voltage won't be great. The 50 Ohm feed through must be
> placed as close as possible to the input of the scope's input
> amplifier which means the BNC input terminal of the scope.
>
> For high speed oscilloscope probes the inner conductor of the coax
> cables are made of resistive wire to dissipate energy along the wire.
> This reduces reflections when the signal reaches the ends of the cable.
>
> I know of a compensation device like used in oscilloscope probes (i.e.
> like 1:10, 1:20, 1:50, 1:100 etc.). But this device is for audio
> signals. He tells that when it's correct adjusted the sound picture
> has depth end everything placed correct. He got the idea from
> oscilloscope probes where you want to see the signal on the screen
> like how it is at the probe tip. Never mind how it looks along the
> signal path as long as the end result is correct. That's what the
> compensation is for. I.e. when the compensation is correct adjusted an
> input square wave looks like a square wave on the screen. Without the
> compensation the corners of the square wave are round. With too much
> compensation the corners becomes pin shaped.
>
> Regards
> Ole
>
>
>
> ---In [email protected], <freeen2012@...> wrote :
>
> Hi Ole,
>
>>     On 22 Nov 2018, at 18:51, onielsen@... <mailto:onielsen@...>
>>     [EVGRAY] <[email protected] <mailto:[email protected]>>
>>     wrote:
>>
>>     Both ways can be used. For low inductance of a current shunt let
>>     the return wire go close to and in parallel with the shunt
>>     resistor to minimize any area for the magnetic field.
>>
>>     Here the return wire is twisted around the current shunt.
>>
>>     Also the 50 Ohm feed through is necessary. Without it a lot of
>>     reflections will happen unless the scope itself has a 50 Ohm
>>     input. As scope inputs usually are 1M Ohm the signal w ill be
>>     reflected due to the great impedance mismatch from 50m Ohm to 1M
>>     Ohm and the signal will drown in noise. 50m Ohm to 50 Ohm reduces
>>     the reflections a lot.
>>
>>     Thanks for the pic (illustrates it well). I already have such a
>>     50 Ohm feed through but never really understood what exactly it
>>     does and therefore have never used it. I understand it has an
>>     impedance of 50 Ohm like the coax cable to prevent reflexions,
>>     yes, but how does it transfer the potential difference to be
>>     measured (over the shunt) to the 1M Ohm impedance input of the
>>     scope. If we had to build such a 50 Ohm feed through what would
>>     we have to do (what is it composed of)? This might help me to
>>     understand how it works. 
>>
>>     Thanks a lot,
>>
>>      Andreas
>>
>

Ole,

Looks like feed forward compensation, sorry wish I could read Danish but
looks like something fun to try.  Current amps have high bandwidth but
in my experience more dc offset from the common emitter input. 

On 11/23/2018 1:33 PM, [email protected] [EVGRAY] wrote:
>  
>
> Hi Mick,
>
> The compensation network sits at the input end of the amplifier. As
> for oscilloscope probe compensations they can be placed at either end
> of the probe cable. As long as the output signal of the speaker is an
> amplified copy of the input signal at the source the compensation does
> its job fine. For an audio amplifier the signal at the speaker
> terminals should be an amplified copy of the signal at the source. If
> placing the compensation at the output end a lot of power is wasted.
> The compensation has its own battery powered amplifier to keep the
> signal level unchanged. The principle is shown in figure 4 here:
> https://ipaper.ipapercms.dk/TechMedia/AktuelElektronik/2007/13/?page=6.
> The compensation (roll-off correction in the article) is inserted in
> the signal chain as shown in figure 3. Figure 2 shows the signals
> without the compensation. His version is switched in steps while
> oscilloscope probes use a variable capacitor.
>
> It is told that by putting resistance in series with the speaker the
> sound is improved. This makes a voltage amplifier act more like a
> current amplifier.
>
> There is an old B&O speaker with high damping that sounds very good
> but wastes a lot of power. It requires quite much power just to
> operate that model at moderate level because of its high damping. I
> don't know if it is damped by resistance or if it is mechanical damped
> or both. A good way of driving a speaker is with a current amplifier
> like used in scopes for their high bandwidth. Of course the output
> current must be greater for driving a speaker. Current amplifiers can
> be made quite simple if using matched pairs of transistors and the
> bandwidth can be something like 40MHZ for standard transistors. This
> is fast enough to give a very good replication of the finer details of
> an audio signal.
>
> Regards
> Ole
>
>
>
> ---In [email protected], <mkjekyll@...> wrote :
>
> Hi Ole,
>
> Same concept we use when designing a zobel network for a transformer
> in a mic preamp.  I suppose this magic device sits near the speaker.  
> I have a hard time believing this would do much with most dynamic
> speakers as the mechanical impedance and reactance makes a square wave
> hard to recognize.  On an electrostatic speaker though one can see a
> pretty good square wave however that is one huge capacitor compared to
> some trimmer so likely would require a tunable inductor in line with
> the step up transformer.  Of course I am referring to using a
> laboratory mic for looking at the square wave not just a probe across
> the speaker terminals.
>
>
> On 11/22/2018 11:29 AM, onielsen@... <mailto:onielsen@...> [EVGRAY] wrote:
>
>>      
>>
>>     Hi Andreas,
>>
>>     Yahoo doesn't like to transfer the complete messages today even
>>     though the delay isn't too great. I completed the message history
>>     from the picture and hope it gets through.
>>
>>     To make your own BNC feed through get one male and one female 50
>>     Ohm connector and an inductance free 50 Ohm resistor. Then
>>     connect them all in parallel. Instead of one 50 Ohm resistor
>>     perhaps use two100 Ohm resistors in parallel. The resistors must
>>     be able to dissipate the power at the max voltage across them.
>>     With a low impedance current shunt this voltage won't be great.
>>     The 50 Ohm feed through must be placed as close as possible to
>>     the input of the scope's input amplifier which means the BNC
>>     input terminal of the scope.
>>
>>     For high speed oscilloscope probes the inner conductor of the
>>     coax cables are made of resistive wire to dissipate energy along
>>     the wire. This reduces reflections when the signal reaches the
>>     ends of the cable.
>>
>>     I know of a compensation device like used in oscilloscope probes
>>     (i.e. like 1:10, 1:20, 1:50, 1:100 etc.). But this device is for
>>     audio signals. He tells that when it's correct adjusted the sound
>>     picture has depth end everything placed correct. He got the idea
>>     from oscilloscope probes where you want to see the signal on the
>>     screen like how it is at the probe tip. Never mind how it looks
>>     along the signal path as long as the end result is correct.
>>     That's what the compensation is for. I.e. when the compensation
>>     is correct adjusted an input square wave looks like a square wave
>>     on the screen. Without the compensation the corners of the square
>>     wave are round. With too much compensation the corners becomes
>>     pin shaped.
>>
>>     Regards
>>     Ole
>>
>>
>>
>>     ---In [email protected] <mailto:[email protected]>,
>>     <freeen2012@...> <mailto:freeen2012@...> wrote :
>>
>>     Hi Ole,
>>
>>>         On 22 Nov 2018, at 18:51, onielsen@... <mailto:onielsen@...>
>>>         [EVGRAY] <[email protected]
>>>         <mailto:[email protected]>> wrote:
>>>
>>>         Both ways can be used. For low inductance of a current shunt
>>>         let the return wire go close to and in parallel with the
>>>         shunt resistor to minimize any area for the magnetic field.
>>>
>>>         Here the return wire is twisted around the current shunt.
>>>
>>>         Also the 50 Ohm feed through is necessary. Without it a lot
>>>         of reflections will happen unless the scope itself has a 50
>>>         Ohm input. As scope inputs usually are 1M Ohm the signal w
>>>         ill be reflected due to the great impedance mismatch from
>>>         50m Ohm to 1M Ohm and the signal will drown in noise. 50m
>>>         Ohm to 50 Ohm reduces the reflections a lot.
>>>
>>>         Thanks for the pic (illustrates it well). I already have
>>>         such a 50 Ohm feed through but never really understood what
>>>         exactly it does and therefore have never used it. I
>>>         understand it has an impedance of 50 Ohm like the coax cable
>>>         to prevent reflexions, yes, but how does it transfer the
>>>         potential difference to be measured (over the shunt) to the
>>>         1M Ohm impedance input of the scope. If we had to build such
>>>         a 50 Ohm feed through what would we have to do (what is it
>>>         composed of)? This might help me to understand how it works. 
>>>
>>>         Thanks a lot,
>>>
>>>          Andreas
>>>
>

Ole,

Current amplifiers are not a really a good choice to drive speakers
anyways as high impedance will get more and more voltage with a CCS. 
Better to use voltage amps biased with current sources.  Dynamic
speakers present a varying impedance bandwidth so tweeters will begin to
clip,  unless the speakers are electrostatic where the impedance rises
as freq drops inverse to dynamics.  Current amps are a good choice for
some preamp circuits though which are driving a less reactive much more
constant impedance and as you claim can then leverage the bandwidth of
transistors.  I am having an issue with a current pre design right now
that has huge bandwidth on the bench.   On a scope impulse response is
flat from several Hz to almost a mHz however when used for recording
real world signals rather than a sweep the low end is much thinner
sounding than it should be.  I will try a diff power supply to see if
massive current reserves will make a difference.

Thanks for the probe link, I will read in a bit.

Interesting enough that audio is normally considered to low freq for
skin effect to matter as most RF engineers will attest but silver plated
oxygen free copper makes a big difference in sound quality.   The old
fashioned wire wrap is often very good for audio as it is silver plated
copper and very thin and very inexpensive.   Good way to make
interconnects that rival those expensive ones for a few bucks.  Coax is
not really good for audio either as presents too many non linearities. 
Audio is a weird duck as to an RF engineer it looks like but a small
notch however there are some really big differentials in that small
window concerning how materials react likely having to do with the long
wavelengths and the (phase?) change around 10kHz where radio emission
begins.  I imagine you can explain this much better than I just did and
I don't know the proper terminology of where AF starts becoming RF which
is much lower then the formal claim of about 100kHz.


On 11/23/2018 6:27 PM, [email protected] [EVGRAY] wrote:
>  
>
> Hi Mick,
>
> Here is an article about oscilloscope probes: 'The Secret World of
> Oscilloscope Probes'
> (http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf).
> It's not only the compensation network that matters. For minimum
> reflections the damping has to be done along the length of the cable.
> Just look at those thin coaxial cables on scope probes. I guess they
> would sound good as audio signal cables if used with the compensation
> network correct adjusted. It does require some extra amplification to
> compensate for the damping.
>
> Regards
> Ole
>
>
>
> ---In [email protected], <mkjekyll@...> wrote :
>
> Ole,
>
> Looks like feed forward compensation, sorry wish I could read Danish
> but looks like something fun to try.  Current amps have high bandwidth
> but in my experience more dc offset from the common emitter input. 
>
> On 11/23/2018 1:33 PM, onielsen@... <mailto:onielsen@...> [EVGRAY] wrote:
>
>>      
>>
>>     Hi Mick,
>>
>>     The compensation network sits at the input end of the amplifier.
>>     As for oscilloscope probe compensations they can be placed at
>>     either end of the probe cable. As long as the output signal of
>>     the speaker is an amplified copy of the input signal at the
>>     source the compensation does its job fine. For an audio amplifier
>>     the signal at the speaker terminals should be an amplified copy
>>     of the signal at the source. If placing the compensation at the
>>     output end a lot of power is wasted. The compensation has its own
>>     battery powered amplifier to keep the signal level unchanged. The
>>     principle is shown in figure 4 here:
>>     https://ipaper.ipapercms.dk/TechMedia/AktuelElektronik/2007/13/?page=6.
>>     The compensation (roll-off correction in the article) is inserted
>>     in the signal chain as shown in figure 3. Figure 2 shows the
>>     signals without the compensation. His version is switched in
>>     steps while oscilloscope probes use a variable capacitor.
>>
>>     It is told that by putting resistance in series with the speaker
>>     the sound is improved. This makes a voltage amplifier act more
>>     like a current amplifier.
>>
>>     There is an old B&O speaker with high damping that sounds very
>>     good but wastes a lot of power. It requires quite much power just
>>     to operate that model at moderate level because of its high
>>     damping. I don't know if it is damped by resistance or if it is
>>     mechanical damped or both. A good way of driving a speaker is
>>     with a current amplifier like used in scopes for their high
>>     bandwidth. Of course the output current must be greater for
>>     driving a speaker. Current amplifiers can be made quite simple if
>>     using matched pairs of transistors and the bandwidth can be
>>     something like 40MHZ for standard transistors. This is fast
>>     enough to give a very good replication of the finer details of an
>>     audio signal.
>>
>>     Regards
>>     Ole
>>
>>
>>
>>     ---In [email protected] <mailto:[email protected]>,
>>     <mkjekyll@...> <mailto:mkjekyll@...> wrote :
>>
>>     Hi Ole,
>>
>>     Same concept we use when designing a zobel network for a
>>     transformer in a mic preamp.  I suppose this magic device sits
>>     near the speaker.   I have a hard time believing this would do
>>     much with most dynamic speakers as the mechanical impedance and
>>     reactance makes a square wave hard to recognize.  On an
>>     electrostatic speaker though one can see a pretty good square
>>     wave however that is one huge capacitor compared to some trimmer
>>     so likely would require a tunable inductor in line with the step
>>     up transformer.  Of course I am referring to using a laboratory
>>     mic for looking at the square wave not just a probe across the
>>     speaker terminals.
>>
>>
>>     On 11/22/2018 11:29 AM, onielsen@... <mailto:onielsen@...>
>>     [EVGRAY] wrote:
>>
>>>          
>>>
>>>         Hi Andreas,
>>>
>>>         Yahoo doesn't like to transfer the complete messages today
>>>         even though the delay isn't too great. I completed the
>>>         message history from the picture and hope it gets through.
>>>
>>>         To make your own BNC feed through get one male and one
>>>         female 50 Ohm connector and an inductance free 50 Ohm
>>>         resistor. Then connect them all in parallel. Instead of one
>>>         50 Ohm resistor perhaps use two100 Ohm resistors in
>>>         parallel. The resistors must be able to dissipate the power
>>>         at the max voltage across them. With a low impedance current
>>>         shunt this voltage won't be great. The 50 Ohm feed through
>>>         must be placed as close as possible to the input of the
>>>         scope's input amplifier which means the BNC input terminal
>>>         of the scope.
>>>
>>>         For high speed oscilloscope probes the inner conductor of
>>>         the coax cables are made of resistive wire to dissipate
>>>         energy along the wire. This reduces reflections when the
>>>         signal reaches the ends of the cable.
>>>
>>>         I know of a compensation device like used in oscilloscope
>>>         probes (i.e. like 1:10, 1:20, 1:50, 1:100 etc.). But this
>>>         device is for audio signals. He tells that when it's correct
>>>         adjusted the sound picture has depth end everything placed
>>>         correct. He got the idea from oscilloscope probes where you
>>>         want to see the signal on the screen like how it is at the
>>>         probe tip. Never mind how it looks along the signal path as
>>>         long as the end result is correct. That's what the
>>>         compensation is for. I.e. when the compensation is correct
>>>         adjusted an input square wave looks like a square wave on
>>>         the screen. Without the compensation the corners of the
>>>         square wave are round. With too much compensation the
>>>         corners becomes pin shaped.
>>>
>>>         Regards
>>>         Ole
>>>
>>>
>>>
>>>         ---In [email protected]
>>>         <mailto:[email protected]>, <freeen2012@...>
>>>         <mailto:freeen2012@...> wrote :
>>>
>>>         Hi Ole,
>>>
>>>>             On 22 Nov 2018, at 18:51, onielsen@...
>>>>             <mailto:onielsen@...> [EVGRAY] <[email protected]
>>>>             <mailto:[email protected]>> wrote:
>>>>
>>>>             Both ways can be used. For low inductance of a current
>>>>             shunt let the return wire go close to and in parallel
>>>>             with the shunt resistor to minimize any area for the
>>>>             magnetic field.
>>>>
>>>>             Here the return wire is twisted around the current shunt.
>>>>
>>>>             Also the 50 Ohm feed through is necessary. Without it a
>>>>             lot of reflections will happen unless the scope itself
>>>>             has a 50 Ohm input. As scope inputs usually are 1M Ohm
>>>>             the signal w ill be reflected due to the great
>>>>             impedance mismatch from 50m Ohm to 1M Ohm and the
>>>>             signal will drown in noise. 50m Ohm to 50 Ohm reduces
>>>>             the reflections a lot.
>>>>
>>>>             Thanks for the pic (illustrates it well). I already
>>>>             have such a 50 Ohm feed through but never really
>>>>             understood what exactly it does and therefore have
>>>>             never used it. I understand it has an impedance of 50
>>>>             Ohm like the coax cable to prevent reflexions, yes, but
>>>>             how does it transfer the potential difference to be
>>>>             measured (over the shunt) to the 1M Ohm impedance input
>>>>             of the scope. If we had to build such a 50 Ohm feed
>>>>             through what would we have to do (what is it composed
>>>>             of)? This might help me to understand how it works. 
>>>>
>>>>             Thanks a lot,
>>>>
>>>>              Andreas
>>>>
>

Hi Mick,

The compensation network sits at the input end of the amplifier. As for oscilloscope probe compensations they can be placed at either end of the probe cable. As long as the output signal of the speaker is an amplified copy of the input signal at the source the compensation does its job fine. For an audio amplifier the signal at the speaker terminals should be an amplified copy of the signal at the source. If placing the compensation at the output end a lot of power is wasted. The compensation has its own battery powered amplifier to keep the signal level unchanged. The principle is shown in figure 4 here: https://ipaper.ipapercms.dk/TechMedia/AktuelElektronik/2007/13/?page=6 https://ipaper.ipapercms.dk/TechMedia/AktuelElektronik/2007/13/?page=6. The compensation (roll-off correction in the article) is inserted in the signal chain as shown in figure 3. Figure 2 shows the signals without the compensation. His version is switched in steps while oscilloscope probes use a variable capacitor.

It is told that by putting resistance in series with the speaker the sound is improved. This makes a voltage amplifier act more like a current amplifier.

There is an old B&O speaker with high damping that sounds very good but wastes a lot of power. It requires quite much power just to operate that model at moderate level because of its high damping. I don't know if it is damped by resistance or if it is mechanical damped or both. A good way of driving a speaker is with a current amplifier like used in scopes for their high bandwidth. Of course the output current must be greater for driving a speaker. Current amplifiers can be made quite simple if using matched pairs of transistors and the bandwidth can be something like 40MHZ for standard transistors. This is fast enough to give a very good replication of the finer details of an audio signal.

Regards
Ole
 

---In [email protected], <mkjekyll@...> wrote :

 Hi Ole,
 Same concept we use when designing a zobel network for a transformer in a mic preamp.  I suppose this magic device sits near the speaker.   I have a hard time believing this would do much with most dynamic speakers as the mechanical impedance and reactance makes a square wave hard to recognize.  On an electrostatic speaker though one can see a pretty good square wave however that is one huge capacitor compared to some trimmer so likely would require a tunable inductor in line with the step up transformer.  Of course I am referring to using a laboratory mic for looking at the square wave not just a probe across the speaker terminals.
 

 On 11/22/2018 11:29 AM, onielsen@... mailto:onielsen@... [EVGRAY] wrote:

   Hi Andreas,
 
 Yahoo doesn't like to transfer the complete messages today even though the delay isn't too great. I completed the message history from the picture and hope it gets through.
 
 To make your own BNC feed through get one male and one female 50 Ohm connector and an inductance free 50 Ohm resistor. Then connect them all in parallel. Instead of one 50 Ohm resistor perhaps use two100 Ohm resistors in parallel. The resistors must be able to dissipate the power at the max voltage across them. With a low impedance current shunt this voltage won't be great. The 50 Ohm feed through must be placed as close as possible to the input of the scope's input amplifier which means the BNC input terminal of the scope.
 
 For high speed oscilloscope probes the inner conductor of the coax cables are made of resistive wire to dissipate energy along the wire. This reduces reflections when the signal reaches the ends of the cable.
 
 I know of a compensation device like used in oscilloscope probes (i.e. like 1:10, 1:20, 1:50, 1:100 etc.). But this device is for audio signals. He tells that when it's correct adjusted the sound picture has depth end everything placed correct. He got the idea from oscilloscope probes where you want to see the signal on the screen like how it is at the probe tip. Never mind how it looks along the signal path as long as the end result is correct. That's what the compensation is for. I.e. when the compensation is correct adjusted an input square wave looks like a square wave on the screen. Without the compensation the corners of the square wave are round. With too much compensation the corners becomes pin shaped.
 
 Regards
 Ole

 
 
 ---In [email protected] mailto:[email protected], <freeen2012@...> mailto:freeen2012@... wrote :
 
 Hi Ole, 
 On 22 Nov 2018, at 18:51, onielsen@... mailto:onielsen@... [EVGRAY] <[email protected] mailto:[email protected]> wrote:
 
 Both ways can be used. For low inductance of a current shunt let the return wire go close to and in parallel with the shunt resistor to minimize any area for the magnetic field.
 
 Here the return wire is twisted around the current shunt.
 
 Also the 50 Ohm feed through is necessary. Without it a lot of reflections will happen unless the scope itself has a 50 Ohm input. As scope inputs usually are 1M Ohm the signal w ill be reflected due to the great impedance mismatch from 50m Ohm to 1M Ohm and the signal will drown in noise. 50m Ohm to 50 Ohm reduces the reflections a lot.
 
 Thanks for the pic (illustrates it well). I already have such a 50 Ohm feed through but never really understood what exactly it does and therefore have never used it. I understand it has an impedance of 50 Ohm like the coax cable to prevent reflexions, yes, but how does it transfer the potential difference to be measured (over the shunt) to the 1M Ohm impedance input of the scope. If we had to build such a 50 Ohm feed through what would we have to do (what is it composed of)? This might help me to understand how it works. 
 
 Thanks a lot,
 

  Andreas

Hi Mick,

Here is an article about oscilloscope probes: 'The Secret World of Oscilloscope Probes' (http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf). It's not only the compensation network that matters. For minimum reflections the damping has to be done along the length of the cable. Just look at those thin coaxial cables on scope probes. I guess they would sound good as audio signal cables if used with the compensation network correct adjusted. It does require some extra amplification to compensate for the damping.

Regards
Ole
 

---In [email protected], <mkjekyll@...> wrote :

 Ole,
 Looks like feed forward compensation, sorry wish I could read Danish but looks like something fun to try.  Current amps have high bandwidth but in my experience more dc offset from the common emitter input.  

 On 11/23/2018 1:33 PM, onielsen@... mailto:onielsen@... [EVGRAY] wrote:

   Hi Mick,
 
 The compensation network sits at the input end of the amplifier. As for oscilloscope probe compensations they can be placed at either end of the probe cable. As long as the output signal of the speaker is an amplified copy of the input signal at the source the compensation does its job fine. For an audio amplifier the signal at the speaker terminals should be an amplified copy of the signal at the source. If placing the compensation at the output end a lot of power is wasted. The compensation has its own battery powered amplifier to keep the signal level unchanged. The principle is shown in figure 4 here: https://ipaper.ipapercms.dk/TechMedia/AktuelElektronik/2007/13/?page=6 https://ipaper.ipapercms.dk/TechMedia/AktuelElektronik/2007/13/?page=6. The compensation (roll-off correction in the article) is inserted in the signal chain as shown in figure 3. Figure 2 shows the signals without the compensation. His version is switched in steps while oscilloscope probes use a variable capacitor.
 
 It is told that by putting resistance in series with the speaker the sound is improved. This makes a voltage amplifier act more like a current amplifier.
 
 There is an old B&O speaker with high damping that sounds very good but wastes a lot of power. It requires quite much power just to operate that model at moderate level because of its high damping. I don't know if it is damped by resistance or if it is mechanical damped or both. A good way of driving a speaker is with a current amplifier like used in scopes for their high bandwidth. Of course the output current must be greater for driving a speaker. Current amplifiers can be made quite simple if using matched pairs of transistors and the bandwidth can be something like 40MHZ for standard transistors. This is fast enough to give a very good replication of the finer details of an audio signal.
 
 Regards
 Ole

 
 
 ---In [email protected] mailto:[email protected], <mkjekyll@...> mailto:mkjekyll@... wrote :
 
 Hi Ole,
 Same concept we use when designing a zobel network for a transformer in a mic preamp.  I suppose this magic device sits near the speaker.   I have a hard time believing this would do much with most dynamic speakers as the mechanical impedance and reactance makes a square wave hard to recognize.  On an electrostatic speaker though one can see a pretty good square wave however that is one huge capacitor compared to some trimmer so likely would require a tunable inductor in line with the step up transformer.  Of course I am referring to using a laboratory mic for looking at the square wave not just a probe across the speaker terminals.
 

 On 11/22/2018 11:29 AM, onielsen@... mailto:onielsen@... [EVGRAY] wrote:

   Hi Andreas,
 
 Yahoo doesn't like to transfer the complete messages today even though the delay isn't too great. I completed the message history from the picture and hope it gets through.
 
 To make your own BNC feed through get one male and one female 50 Ohm connector and an inductance free 50 Ohm resistor. Then connect them all in parallel. Instead of one 50 Ohm resistor perhaps use two100 Ohm resistors in parallel. The resistors must be able to dissipate the power at the max voltage across them. With a low impedance current shunt this voltage won't be great. The 50 Ohm feed through must be placed as close as possible to the input of the scope's input amplifier which means the BNC input terminal of the scope.
 
 For high speed oscilloscope probes the inner conductor of the coax cables are made of resistive wire to dissipate energy along the wire. This reduces reflections when the signal reaches the ends of the cable.
 
 I know of a compensation device like used in oscilloscope probes (i.e. like 1:10, 1:20, 1:50, 1:100 etc.). But this device is for audio signals. He tells that when it's correct adjusted the sound picture has depth end everything placed correct. He got the idea from oscilloscope probes where you want to see the signal on the screen like how it is at the probe tip. Never mind how it looks along the signal path as long as the end result is correct. That's what the compensation is for. I.e. when the compensation is correct adjusted an input square wave looks like a square wave on the screen. Without the compensation the corners of the square wave are round. With too much compensation the corners becomes pin shaped.
 
 Regards
 Ole

 
 
 ---In [email protected] mailto:[email protected], <freeen2012@...> mailto:freeen2012@... wrote :
 
 Hi Ole, 
 On 22 Nov 2018, at 18:51, onielsen@... mailto:onielsen@... [EVGRAY] <[email protected] mailto:[email protected]> wrote:
 
 Both ways can be used. For low inductance of a current shunt let the return wire go close to and in parallel with the shunt resistor to minimize any area for the magnetic field.
 
 Here the return wire is twisted around the current shunt.
 
 Also the 50 Ohm feed through is necessary. Without it a lot of reflections will happen unless the scope itself has a 50 Ohm input. As scope inputs usually are 1M Ohm the signal w ill be reflected due to the great impedance mismatch from 50m Ohm to 1M Ohm and the signal will drown in noise. 50m Ohm to 50 Ohm reduces the reflections a lot.
 
 Thanks for the pic (illustrates it well). I already have such a 50 Ohm feed through but never really understood what exactly it does and therefore have never used it. I understand it has an impedance of 50 Ohm like the coax cable to prevent reflexions, yes, but how does it transfer the potential difference to be measured (over the shunt) to the 1M Ohm impedance input of the scope. If we had to build such a 50 Ohm feed through what would we have to do (what is it composed of)? This might help me to understand how it works. 
 
 Thanks a lot,
 

  Andreas

Ole,

Yes the current buffer at the output end of the amp decauples the
voltage amp from speaker reactance and is required and the more current
the better all power amps have a basic currrent amp at the output. Most
amp designs are hybrids.  As you say with audio there are so many
octaves and the impedance and reactance are non linear into a cored
inductor, specially one that is a motor also reacting to air loading
modes.  A DC motor will speed up to destruction with unlimited voltage
so what happens when the impedance goes super high or the speakers are
not connected with an ideal pure CCS amp?
Bass at the lowest impedance needs the most current.  Highs like fast
non slew rate limited voltage.  Wrapping a design in loop feedback to
keep it stable is really not good sounding and lazy practice but
sometimes required. I use a curve tracer to match parts.  Local
degenerative feedback not an issue sonically but when it's wrapped
around a whole circuit looped from out to in, yuck, at least have the
individual parts nested.

One of the biggest problems with audio designing is we cant test what is
really going on wideband with music only guess or listen.  Something
that looks great with pink noise or impulse responsed can in practice
not sound so good.  Why many afficianados like SET designs because it's
just one single ended tube without all the garbage, while not so good
for rock and roll or stunning dynamics for less bombastic music the
imaging can be superlative.

For audio designs I really think Nelson Pass is solid, big respect
here.  In pro audio we like a shitload more watts on standby as every
extra frequency divides power but for home gear can't go wrong with
Nelsons designs and they are cheap and fun to build.
http://www.firstwatt.com/faq.html

Also a really good sound resource is Rod Elliot
http://sound.whsites.net/index2.html

This article goes into some of what we are talking about:
http://sound.whsites.net/project56.htm


On 11/24/2018 4:18 AM, [email protected] [EVGRAY] wrote:
>  
>
> Hi  Mick,
>
> The person here: http://nov79.com/amr/cont.htm claims that current
> amplifiers are the best way to drive speakers. Citing from page two:
> "The current amplifier drives the speakers. It has no effect upon the
> signal. It is the perfect black box which allows the voltage amplifier
> to drive a heavy load as if it were no load at all."
>
> The only problem is for mass production as the two PNP transistors and
> the two NPN transistors must be matched. For low signal the solution
> is buying the transistors as IC packages as they're matched by using
> the same crystal for all four transistors. The person describes three
> sizes of amplifiers.
>
> This could be used for making a cheap differential probe or current
> probe amplifier for scopes. The conventional ones are pretty expensive
> to buy.
>
> "Audio is a weird duck as to an RF engineer it looks like but a small
> notch however there are some really big differentials in that small
> window concerning how materials react likely having to do with the
> long wavelengths and the (phase?) change around 10kHz where radio
> emission begins."
> To cover the hearing range of human ears the amplifier has to cover
> around seven octaves. That's pretty much. A human eye sees only one
> octave. A RF transmitter may be even more limited.
>
> Regards
> Ole
>
>
>
> ---In [email protected], <mkjekyll@...> wrote :
>
> Ole,
>
> Current amplifiers are not a really a good choice to drive speakers
> anyways as high impedance will get more and more voltage with a CCS. 
> Better to use voltage amps biased with current sources.  Dynamic
> speakers present a varying impedance bandwidth so tweeters will begin
> to clip,  unless the speakers are electrostatic where the impedance
> rises as freq drops inverse to dynamics.  Current amps are a good
> choice for some preamp circuits though which are driving a less
> reactive much more constant impedance and as you claim can then
> leverage the bandwidth of transistors.  I am having an issue with a
> current pre design right now that has huge bandwidth on the bench.  
> On a scope impulse response is flat from several Hz to almost a mHz
> however when used for recording real world signals rather than a sweep
> the low end is much thinner sounding than it should be.  I will try a
> diff power supply to see if massive current reserves will make a
> difference.
>
> Thanks for the probe link, I will read in a bit.
>
> Interesting enough that audio is normally considered to low freq for
> skin effect to matter as most RF engineers will attest but silver
> plated oxygen free copper makes a big difference in sound quality.  
> The old fashioned wire wrap is often very good for audio as it is
> silver plated copper and very thin and very inexpensive.   Good way to
> make interconnects that rival those expensive ones for a few bucks. 
> Coax is not really good for audio either as presents too many non
> linearities.  Audio is a weird duck as to an RF engineer it looks like
> but a small notch however there are some really big differentials in
> that small window concerning how materials react likely having to do
> with the long wavelengths and the (phase?) change around 10kHz where
> radio emission begins.  I imagine you can explain this much better
> than I just did and I don't know the proper terminology of where AF
> starts becoming RF which is much lower then the formal claim of about
> 100kHz.
>
>
> On 11/23/2018 6:27 PM, onielsen@... <mailto:onielsen@...> [EVGRAY] wrote:
>
>>      
>>
>>     Hi Mick,
>>
>>     Here is an article about oscilloscope probes: 'The Secret World
>>     of Oscilloscope Probes'
>>     (http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf).
>>     It's not only the compensation network that matters. For minimum
>>     reflections the damping has to be done along the length of the
>>     cable. Just look at those thin coaxial cables on scope probes. I
>>     guess they would sound good as audio signal cables if used with
>>     the compensation network correct adjusted. It does require some
>>     extra amplification to compensate for the damping.
>>
>>     Regards
>>     Ole
>>
>>
>>
>>     ---In [email protected] <mailto:[email protected]>,
>>     <mkjekyll@...> <mailto:mkjekyll@...> wrote :
>>
>>     Ole,
>>
>>     Looks like feed forward compensation, sorry wish I could read
>>     Danish but looks like something fun to try.  Current amps have
>>     high bandwidth but in my experience more dc offset from the
>>     common emitter input. 
>>
>>     On 11/23/2018 1:33 PM, onielsen@... <mailto:onielsen@...>
>>     [EVGRAY] wrote:
>>
>>>          
>>>
>>>         Hi Mick,
>>>
>>>         The compensation network sits at the input end of the
>>>         amplifier. As for oscilloscope probe compensations they can
>>>         be placed at either end of the probe cable. As long as the
>>>         output signal of the speaker is an amplified copy of the
>>>         input signal at the source the compensation does its job
>>>         fine. For an audio amplifier the signal at the speaker
>>>         terminals should be an amplified copy of the signal at the
>>>         source. If placing the compensation at the output end a lot
>>>         of power is wasted. The compensation has its own battery
>>>         powered amplifier to keep the signal level unchanged. The
>>>         principle is shown in figure 4 here:
>>>         https://ipaper.ipapercms.dk/TechMedia/AktuelElektronik/2007/13/?page=6.
>>>         The compensation (roll-off correction in the article) is
>>>         inserted in the signal chain as shown in figure 3. Figure 2
>>>         shows the signals without the compensation. His version is
>>>         switched in steps while oscilloscope probes use a variable
>>>         capacitor.
>>>
>>>         It is told that by putting resistance in series with the
>>>         speaker the sound is improved. This makes a voltage
>>>         amplifier act more like a current amplifier.
>>>
>>>         There is an old B&O speaker with high damping that sounds
>>>         very good but wastes a lot of power. It requires quite much
>>>         power just to operate that model at moderate level because
>>>         of its high damping. I don't know if it is damped by
>>>         resistance or if it is mechanical damped or both. A good way
>>>         of driving a speaker is with a current amplifier like used
>>>         in scopes for their high bandwidth. Of course the output
>>>         current must be greater for driving a speaker. Current
>>>         amplifiers can be made quite simple if using matched pairs
>>>         of transistors and the bandwidth can be something like 40MHZ
>>>         for standard transistors. This is fast enough to give a very
>>>         good replication of the finer details of an audio signal.
>>>
>>>         Regards
>>>         Ole
>>>
>>>
>>>
>>>         ---In [email protected]
>>>         <mailto:[email protected]>, <mkjekyll@...>
>>>         <mailto:mkjekyll@...> wrote :
>>>
>>>         Hi Ole,
>>>
>>>         Same concept we use when designing a zobel network for a
>>>         transformer in a mic preamp.  I suppose this magic device
>>>         sits near the speaker.   I have a hard time believing this
>>>         would do much with most dynamic speakers as the mechanical
>>>         impedance and reactance makes a square wave hard to
>>>         recognize.  On an electrostatic speaker though one can see a
>>>         pretty good square wave however that is one huge capacitor
>>>         compared to some trimmer so likely would require a tunable
>>>         inductor in line with the step up transformer.  Of course I
>>>         am referring to using a laboratory mic for looking at the
>>>         square wave not just a probe across the speaker terminals.
>>>
>>>
>>>         On 11/22/2018 11:29 AM, onielsen@... <mailto:onielsen@...>
>>>         [EVGRAY] wrote:
>>>
>>>>              
>>>>
>>>>             Hi Andreas,
>>>>
>>>>             Yahoo doesn't like to transfer the complete messages
>>>>             today even though the delay isn't too great. I
>>>>             completed the message history from the picture and hope
>>>>             it gets through.
>>>>
>>>>             To make your own BNC feed through get one male and one
>>>>             female 50 Ohm connector and an inductance free 50 Ohm
>>>>             resistor. Then connect them all in parallel. Instead of
>>>>             one 50 Ohm resistor perhaps use two100 Ohm resistors in
>>>>             parallel. The resistors must be able to dissipate the
>>>>             power at the max voltage across them. With a low
>>>>             impedance current shunt this voltage won't be great.
>>>>             The 50 Ohm feed through must be placed as close as
>>>>             possible to the input of the scope's input amplifier
>>>>             which means the BNC input terminal of the scope.
>>>>
>>>>             For high speed oscilloscope probes the inner conductor
>>>>             of the coax cables are made of resistive wire to
>>>>             dissipate energy along the wire. This reduces
>>>>             reflections when the signal reaches the ends of the cable.
>>>>
>>>>             I know of a compensation device like used in
>>>>             oscilloscope probes (i.e. like 1:10, 1:20, 1:50, 1:100
>>>>             etc.). But this device is for audio signals. He tells
>>>>             that when it's correct adjusted the sound picture has
>>>>             depth end everything placed correct. He got the idea
>>>>             from oscilloscope probes where you want to see the
>>>>             signal on the screen like how it is at the probe tip.
>>>>             Never mind how it looks along the signal path as long
>>>>             as the end result is correct. That's what the
>>>>             compensation is for. I.e. when the compensation is
>>>>             correct adjusted an input square wave looks like a
>>>>             square wave on the screen. Without the compensation the
>>>>             corners of the square wave are round. With too much
>>>>             compensation the corners becomes pin shaped.
>>>>
>>>>             Regards
>>>>             Ole
>>>>
>>>>
>>>>
>>>>             ---In [email protected]
>>>>             <mailto:[email protected]>, <freeen2012@...>
>>>>             <mailto:freeen2012@...> wrote :
>>>>
>>>>             Hi Ole,
>>>>
>>>>>                 On 22 Nov 2018, at 18:51, onielsen@...
>>>>>                 <mailto:onielsen@...> [EVGRAY]
>>>>>                 <[email protected]
>>>>>                 <mailto:[email protected]>> wrote:
>>>>>
>>>>>                 Both ways can be used. For low inductance of a
>>>>>                 current shunt let the return wire go close to and
>>>>>                 in parallel with the shunt resistor to minimize
>>>>>                 any area for the magnetic field.
>>>>>
>>>>>                 Here the return wire is twisted around the current
>>>>>                 shunt.
>>>>>
>>>>>                 Also the 50 Ohm feed through is necessary. Without
>>>>>                 it a lot of reflections will happen unless the
>>>>>                 scope itself has a 50 Ohm input. As scope inputs
>>>>>                 usually are 1M Ohm the signal w ill be reflected
>>>>>                 due to the great impedance mismatch from 50m Ohm
>>>>>                 to 1M Ohm and the signal will drown in noise. 50m
>>>>>                 Ohm to 50 Ohm reduces the reflections a lot.
>>>>>
>>>>>                 Thanks for the pic (illustrates it well). I
>>>>>                 already have such a 50 Ohm feed through but never
>>>>>                 really understood what exactly it does and
>>>>>                 therefore have never used it. I understand it has
>>>>>                 an impedance of 50 Ohm like the coax cable to
>>>>>                 prevent reflexions, yes, but how does it transfer
>>>>>                 the potential difference to be measured (over the
>>>>>                 shunt) to the 1M Ohm impedance input of the scope.
>>>>>                 If we had to build such a 50 Ohm feed through what
>>>>>                 would we have to do (what is it composed of)? This
>>>>>                 might help me to understand how it works. 
>>>>>
>>>>>                 Thanks a lot,
>>>>>
>>>>>                  Andreas
>>>>>
>

Ole,

An amp built with super high Q inductor current sources, sounds like RF
I don't think my tweeters would enjoy that either or the transformers in
the electrostatics.

Her amp is interesting yes, I have spoken to her before and would love
to hear it, but transformers have their issues too.  Most of the wire
with gain designers steer clear of transformers for audio as among other
things they can mess up the fast transient low frequencies due to
saturation. Tube distortion is a flawed concept from 1950's designs.  In
fact much of the distortion attributed to tubes is from the
transformers. Properly designed modern CCS biased tube circuits with
properly designed cathode follower buffers have as low distortion as
solid state and less distortion in the factors unmeasured. Solid state
is like sending music through a rock, tubes do not smear audio like
rocks because there is nothing in the way of hollow state.  How does one
measure IM with actual music...  When working with live instruments and
not smashing everything through compression the instantaneous peaks can
and do make solid state far more distorted.  And it depends on circuit
topology as FET's produce more even harmonics than do tubes due to their
transfer function.

Step response does not provide the full picture but is a good starting
point.  Sounds waves in real life are going in multiple directions
sinking and sourcing at the same time, direct and reflected phase
modulations etc the level of vector analysis would be crazy to know what
is really happening.  I have heard amps with excellent step response
almost unmeasurable TIM and Harmonic distortion  that sound like crap
because as you say all of the components to correlate and correct or
else some other reason.  When the infinite network analyzer is built
then we will get much further.  For now audio is still a somewhat black
art.  When I find problems with a piece of gear someone has designed
that is often the comeback, "the impulse step response is as close to
perfect as possible in theory at room temperature".  As I said before
plug a bass guitar in and that preamp that claims flat down two 2 Hz
suddenly sounds anemic and weak.

On 11/24/2018 9:08 AM, [email protected] [EVGRAY] wrote:
>  
>
> Hi Mick,
>
> The current amplifier isn't ideal and as such has limited voltage
> swings. The output can't swing further than the supply voltage. A high
> Q inductor is closer to an ideal current source when disrupting the
> current through it. The voltage may reach high enough to punch through
> the insulation of the wire just to keep the current at the value it
> had during disconnection.
>
> The problem of amplifiers is also the use of lots of components in the
> signal path. Each component has its own resonance frequency because of
> not being ideal components. The feedback loop is for compensating for
> those errors. One solution to this is a wire with amplification or
> next to that an amplifier with a single stage or active component in
> the signal path like in the Zeus amplifier. This is like an old tube
> amplifier but with a modern transistor instead of the very distorting
> tubes (even though the distorted sound of tubes sound good in human ears).
>
> The Zeus amplifier: http://www.susan-parker.co.uk/zeus.htm
>
> "One of the biggest problems with audio designing is we cant test what
> is really going on wideband with music only guess or listen."
> Give it a step response by using a square wave as input. If not coming
> out as a sharp square wave the signal has changed. Just look at the
> oscilloscope probe for how to correct that. It costs a lot of
> amplification though.
>
> Regards
> Ole
>
>
> ---In [email protected], <mkjekyll@...> wrote :
>
> Ole,
>
> Yes the current buffer at the output end of the amp decauples the
> voltage amp from speaker reactance and is required and the more
> current the better all power amps have a basic currrent amp at the
> output. Most amp designs are hybrids.  As you say with audio there are
> so many octaves and the impedance and reactance are non linear into a
> cored inductor, specially one that is a motor also reacting to air
> loading modes.  A DC motor will speed up to destruction with unlimited
> voltage so what happens when the impedance goes super high or the
> speakers are not connected with an ideal pure CCS amp?
> Bass at the lowest impedance needs the most current.  Highs like fast
> non slew rate limited voltage.  Wrapping a design in loop feedback to
> keep it stable is really not good sounding and lazy practice but
> sometimes required. I use a curve tracer to match parts.  Local
> degenerative feedback not an issue sonically but when it's wrapped
> around a whole circuit looped from out to in, yuck, at least have the
> individual parts nested.
>
> One of the biggest problems with audio designing is we cant test what
> is really going on wideband with music only guess or listen. 
> Something that looks great with pink noise or impulse responsed can in
> practice not sound so good.  Why many afficianados like SET designs
> because it's just one single ended tube without all the garbage, while
> not so good for rock and roll or stunning dynamics for less bombastic
> music the imaging can be superlative.
>
> For audio designs I really think Nelson Pass is solid, big respect
> here.  In pro audio we like a shitload more watts on standby as every
> extra frequency divides power but for home gear can't go wrong with
> Nelsons designs and they are cheap and fun to build.
> http://www.firstwatt.com/faq.html
>
> Also a really good sound resource is Rod Elliot
> http://sound.whsites.net/index2.html
>
> This article goes into some of what we are talking about:
> http://sound.whsites.net/project56.htm
>
>
> On 11/24/2018 4:18 AM, onielsen@... <mailto:onielsen@...> [EVGRAY] wrote:
>
>>      
>>
>>     Hi  Mick,
>>
>>     The person here: http://nov79.com/amr/cont.htm claims that
>>     current amplifiers are the best way to drive speakers. Citing
>>     from page two:
>>     "The current amplifier drives the speakers. It has no effect upon
>>     the signal. It is the perfect black box which allows the voltage
>>     amplifier to drive a heavy load as if it were no load at all."
>>
>>     The only problem is for mass production as the two PNP
>>     transistors and the two NPN transistors must be matched. For low
>>     signal the solution is buying the transistors as IC packages as
>>     they're matched by using the same crystal for all four
>>     transistors. The person describes three sizes of amplifiers.
>>
>>     This could be used for making a cheap differential probe or
>>     current probe amplifier for scopes. The conventional ones are
>>     pretty expensive to buy.
>>
>>     "Audio is a weird duck as to an RF engineer it looks like but a
>>     small notch however there are some really big differentials in
>>     that small window concerning how materials react likely having to
>>     do with the long wavelengths and the (phase?) change around 10kHz
>>     where radio emission begins."
>>     To cover the hearing range of human ears the amplifier has to
>>     cover around seven octaves. That's pretty much. A human eye sees
>>     only one octave. A RF transmitter may be even more limited.
>>
>>     Regards
>>     Ole
>>
>>
>>
>>     ---In [email protected] <mailto:[email protected]>,
>>     <mkjekyll@...> <mailto:mkjekyll@...> wrote :
>>
>>     Ole,
>>
>>     Current amplifiers are not a really a good choice to drive
>>     speakers anyways as high impedance will get more and more voltage
>>     with a CCS.  Better to use voltage amps biased with current
>>     sources.  Dynamic speakers present a varying impedance bandwidth
>>     so tweeters will begin to clip,  unless the speakers are
>>     electrostatic where the impedance rises as freq drops inverse to
>>     dynamics.  Current amps are a good choice for some preamp
>>     circuits though which are driving a less reactive much more
>>     constant impedance and as you claim can then leverage the
>>     bandwidth of transistors.  I am having an issue with a current
>>     pre design right now that has huge bandwidth on the bench.   On a
>>     scope impulse response is flat from several Hz to almost a mHz
>>     however when used for recording real world signals rather than a
>>     sweep the low end is much thinner sounding than it should be.  I
>>     will try a diff power supply to see if massive current reserves
>>     will make a difference.
>>
>>     Thanks for the probe link, I will read in a bit.
>>
>>     Interesting enough that audio is normally considered to low freq
>>     for skin effect to matter as most RF engineers will attest but
>>     silver plated oxygen free copper makes a big difference in sound
>>     quality.   The old fashioned wire wrap is often very good for
>>     audio as it is silver plated copper and very thin and very
>>     inexpensive.   Good way to make interconnects that rival those
>>     expensive ones for a few bucks.  Coax is not really good for
>>     audio either as presents too many non linearities.  Audio is a
>>     weird duck as to an RF engineer it looks like but a small notch
>>     however there are some really big differentials in that small
>>     window concerning how materials react likely having to do with
>>     the long wavelengths and the (phase?) change around 10kHz where
>>     radio emission begins.  I imagine you can explain this much
>>     better than I just did and I don't know the proper terminology of
>>     where AF starts becoming RF which is much lower then the formal
>>     claim of about 100kHz.
>>
>>
>>     On 11/23/2018 6:27 PM, onielsen@... <mailto:onielsen@...>
>>     [EVGRAY] wrote:
>>
>>>          
>>>
>>>         Hi Mick,
>>>
>>>         Here is an article about oscilloscope probes: 'The Secret
>>>         World of Oscilloscope Probes'
>>>         (http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf).
>>>         It's not only the compensation network that matters. For
>>>         minimum reflections the damping has to be done along the
>>>         length of the cable. Just look at those thin coaxial cables
>>>         on scope probes. I guess they would sound good as audio
>>>         signal cables if used with the compensation network correct
>>>         adjusted. It does require some extra amplification to
>>>         compensate for the damping.
>>>
>>>         Regards
>>>         Ole
>>>
>>>
>>>
>>>         ---In [email protected]
>>>         <mailto:[email protected]>, <mkjekyll@...>
>>>         <mailto:mkjekyll@...> wrote :
>>>
>>>         Ole,
>>>
>>>         Looks like feed forward compensation, sorry wish I could
>>>         read Danish but looks like something fun to try.  Current
>>>         amps have high bandwidth but in my experience more dc offset
>>>         from the common emitter input. 
>>>
>>>         On 11/23/2018 1:33 PM, onielsen@... <mailto:onielsen@...>
>>>         [EVGRAY] wrote:
>>>
>>>>              
>>>>
>>>>             Hi Mick,
>>>>
>>>>             The compensation network sits at the input end of the
>>>>             amplifier. As for oscilloscope probe compensations they
>>>>             can be placed at either end of the probe cable. As long
>>>>             as the output signal of the speaker is an amplified
>>>>             copy of the input signal at the source the compensation
>>>>             does its job fine. For an audio amplifier the signal at
>>>>             the speaker terminals should be an amplified copy of
>>>>             the signal at the source. If placing the compensation
>>>>             at the output end a lot of power is wasted. The
>>>>             compensation has its own battery powered amplifier to
>>>>             keep the signal level unchanged. The principle is shown
>>>>             in figure 4 here:
>>>>             https://ipaper.ipapercms.dk/TechMedia/AktuelElektronik/2007/13/?page=6.
>>>>             The compensation (roll-off correction in the article)
>>>>             is inserted in the signal chain as shown in figure 3.
>>>>             Figure 2 shows the signals without the compensation.
>>>>             His version is switched in steps while oscilloscope
>>>>             probes use a variable capacitor.
>>>>
>>>>             It is told that by putting resistance in series with
>>>>             the speaker the sound is improved. This makes a voltage
>>>>             amplifier act more like a current amplifier.
>>>>
>>>>             There is an old B&O speaker with high damping that
>>>>             sounds very good but wastes a lot of power. It requires
>>>>             quite much power just to operate that model at moderate
>>>>             level because of its high damping. I don't know if it
>>>>             is damped by resistance or if it is mechanical damped
>>>>             or both. A good way of driving a speaker is with a
>>>>             current amplifier like used in scopes for their high
>>>>             bandwidth. Of course the output current must be greater
>>>>             for driving a speaker. Current amplifiers can be made
>>>>             quite simple if using matched pairs of transistors and
>>>>             the bandwidth can be something like 40MHZ for standard
>>>>             transistors. This is fast enough to give a very good
>>>>             replication of the finer details of an audio signal.
>>>>
>>>>             Regards
>>>>             Ole
>>>>
>>>>
>>>>
>>>>             ---In [email protected]
>>>>             <mailto:[email protected]>, <mkjekyll@...>
>>>>             <mailto:mkjekyll@...> wrote :
>>>>
>>>>             Hi Ole,
>>>>
>>>>             Same concept we use when designing a zobel network for
>>>>             a transformer in a mic preamp.  I suppose this magic
>>>>             device sits near the speaker.   I have a hard time
>>>>             believing this would do much with most dynamic speakers
>>>>             as the mechanical impedance and reactance makes a
>>>>             square wave hard to recognize.  On an electrostatic
>>>>             speaker though one can see a pretty good square wave
>>>>             however that is one huge capacitor compared to some
>>>>             trimmer so likely would require a tunable inductor in
>>>>             line with the step up transformer.  Of course I am
>>>>             referring to using a laboratory mic for looking at the
>>>>             square wave not just a probe across the speaker terminals.
>>>>
>>>>
>>>>             On 11/22/2018 11:29 AM, onielsen@...
>>>>             <mailto:onielsen@...> [EVGRAY] wrote:
>>>>
>>>>>                  
>>>>>
>>>>>                 Hi Andreas,
>>>>>
>>>>>                 Yahoo doesn't like to transfer the complete
>>>>>                 messages today even though the delay isn't too
>>>>>                 great. I completed the message history from the
>>>>>                 picture and hope it gets through.
>>>>>
>>>>>                 To make your own BNC feed through get one male and
>>>>>                 one female 50 Ohm connector and an inductance free
>>>>>                 50 Ohm resistor. Then connect them all in
>>>>>                 parallel. Instead of one 50 Ohm resistor perhaps
>>>>>                 use two100 Ohm resistors in parallel. The
>>>>>                 resistors must be able to dissipate the power at
>>>>>                 the max voltage across them. With a low impedance
>>>>>                 current shunt this voltage won't be great. The 50
>>>>>                 Ohm feed through must be placed as close as
>>>>>                 possible to the input of the scope's input
>>>>>                 amplifier which means the BNC input terminal of
>>>>>                 the scope.
>>>>>
>>>>>                 For high speed oscilloscope probes the inner
>>>>>                 conductor of the coax cables are made of resistive
>>>>>                 wire to dissipate energy along the wire. This
>>>>>                 reduces reflections when the signal reaches the
>>>>>                 ends of the cable.
>>>>>
>>>>>                 I know of a compensation device like used in
>>>>>                 oscilloscope probes (i.e. like 1:10, 1:20, 1:50,
>>>>>                 1:100 etc.). But this device is for audio signals.
>>>>>                 He tells that when it's correct adjusted the sound
>>>>>                 picture has depth end everything placed correct.
>>>>>                 He got the idea from oscilloscope probes where you
>>>>>                 want to see the signal on the screen like how it
>>>>>                 is at the probe tip. Never mind how it looks along
>>>>>                 the signal path as long as the end result is
>>>>>                 correct. That's what the compensation is for. I.e.
>>>>>                 when the compensation is correct adjusted an input
>>>>>                 square wave looks like a square wave on the
>>>>>                 screen. Without the compensation the corners of
>>>>>                 the square wave are round. With too much
>>>>>                 compensation the corners becomes pin shaped.
>>>>>
>>>>>                 Regards
>>>>>                 Ole
>>>>>
>>>>>
>>>>>
>>>>>                 ---In [email protected]
>>>>>                 <mailto:[email protected]>, <freeen2012@...>
>>>>>                 <mailto:freeen2012@...> wrote :
>>>>>
>>>>>                 Hi Ole,
>>>>>
>>>>>>                     On 22 Nov 2018, at 18:51, onielsen@...
>>>>>>                     <mailto:onielsen@...> [EVGRAY]
>>>>>>                     <[email protected]
>>>>>>                     <mailto:[email protected]>> wrote:
>>>>>>
>>>>>>                     Both ways can be used. For low inductance of
>>>>>>                     a current shunt let the return wire go close
>>>>>>                     to and in parallel with the shunt resistor to
>>>>>>                     minimize any area for the magnetic field.
>>>>>>
>>>>>>                     Here the return wire is twisted around the
>>>>>>                     current shunt.
>>>>>>
>>>>>>                     Also the 50 Ohm feed through is necessary.
>>>>>>                     Without it a lot of reflections will happen
>>>>>>                     unless the scope itself has a 50 Ohm input.
>>>>>>                     As scope inputs usually are 1M Ohm the signal
>>>>>>                     w ill be reflected due to the great impedance
>>>>>>                     mismatch from 50m Ohm to 1M Ohm and the
>>>>>>                     signal will drown in noise. 50m Ohm to 50 Ohm
>>>>>>                     reduces the reflections a lot.
>>>>>>
>>>>>>                     Thanks for the pic (illustrates it well). I
>>>>>>                     already have such a 50 Ohm feed through but
>>>>>>                     never really understood what exactly it does
>>>>>>                     and therefore have never used it. I
>>>>>>                     understand it has an impedance of 50 Ohm like
>>>>>>                     the coax cable to prevent reflexions, yes,
>>>>>>                     but how does it transfer the potential
>>>>>>                     difference to be measured (over the shunt) to
>>>>>>                     the 1M Ohm impedance input of the scope. If
>>>>>>                     we had to build such a 50 Ohm feed through
>>>>>>                     what would we have to do (what is it composed
>>>>>>                     of)? This might help me to understand how it
>>>>>>                     works. 
>>>>>>
>>>>>>                     Thanks a lot,
>>>>>>
>>>>>>                      Andreas
>>>>>>
>

Hi  Mick,

The person here: http://nov79.com/amr/cont.htm http://nov79.com/amr/cont.htm claims that current amplifiers are the best way to drive speakers. Citing from page two:
"The current amplifier drives the speakers. It has no effect upon the signal. It is the perfect black box which allows the voltage amplifier to drive a heavy load as if it were no load at all."

The only problem is for mass production as the two PNP transistors and the two NPN transistors must be matched. For low signal the solution is buying the transistors as IC packages as they're matched by using the same crystal for all four transistors. The person describes three sizes of amplifiers.

This could be used for making a cheap differential probe or current probe amplifier for scopes. The conventional ones are pretty expensive to buy.

"Audio is a weird duck as to an RF engineer it looks like but a small notch however there are some really big differentials in that small window concerning how materials react likely having to do with the long wavelengths and the (phase?) change around 10kHz where radio emission begins."
To cover the hearing range of human ears the amplifier has to cover around seven octaves. That's pretty much. A human eye sees only one octave. A RF transmitter may be even more limited.

Regards
Ole
 

---In [email protected], <mkjekyll@...> wrote :

 Ole, 

 Current amplifiers are not a really a good choice to drive speakers anyways as high impedance will get more and more voltage with a CCS.  Better to use voltage amps biased with current sources.  Dynamic speakers present a varying impedance bandwidth so tweeters will begin to clip,  unless the speakers are electrostatic where the impedance rises as freq drops inverse to dynamics.  Current amps are a good choice for some preamp circuits though which are driving a less reactive much more constant impedance and as you claim can then leverage the bandwidth of transistors.  I am having an issue with a current pre design right now that has huge bandwidth on the bench.   On a scope impulse response is flat from several Hz to almost a mHz however when used for recording real world signals rather than a sweep the low end is much thinner sounding than it should be.  I will try a diff power supply to see if massive current reserves will make a difference.

 Thanks for the probe link, I will read in a bit.

 Interesting enough that audio is normally considered to low freq for skin effect to matter as most RF engineers will attest but silver plated oxygen free copper makes a big difference in sound quality.   The old fashioned wire wrap is often very good for audio as it is silver plated copper and very thin and very inexpensive.   Good way to make interconnects that rival those expensive ones for a few bucks.  Coax is not really good for audio either as presents too many non linearities.  Audio is a weird duck as to an RF engineer it looks like but a small notch however there are some really big differentials in that small window concerning how materials react likely having to do with the long wavelengths and the (phase?) change around 10kHz where radio emission begins.  I imagine you can explain this much better than I just did and I don't know the proper terminology of where AF starts becoming RF which is much lower then the formal claim of about 100kHz.
 

 On 11/23/2018 6:27 PM, onielsen@... mailto:onielsen@... [EVGRAY] wrote:

   Hi Mick,
 
 Here is an article about oscilloscope probes: 'The Secret World of Oscilloscope Probes' (http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf). It's not only the compensation network that matters. For minimum reflections the damping has to be done along the length of the cable. Just look at those thin coaxial cables on scope probes. I guess they would sound good as audio signal cables if used with the compensation network correct adjusted. It does require some extra amplification to compensate for the damping.
 
 Regards
 Ole

 
 
 ---In [email protected] mailto:[email protected], <mkjekyll@...> mailto:mkjekyll@... wrote :
 
 Ole,
 Looks like feed forward compensation, sorry wish I could read Danish but looks like something fun to try.  Current amps have high bandwidth but in my experience more dc offset from the common emitter input.  

 On 11/23/2018 1:33 PM, onielsen@... mailto:onielsen@... [EVGRAY] wrote:

   Hi Mick,
 
 The compensation network sits at the input end of the amplifier. As for oscilloscope probe compensations they can be placed at either end of the probe cable. As long as the output signal of the speaker is an amplified copy of the input signal at the source the compensation does its job fine. For an audio amplifier the signal at the speaker terminals should be an amplified copy of the signal at the source. If placing the compensation at the output end a lot of power is wasted. The compensation has its own battery powered amplifier to keep the signal level unchanged. The principle is shown in figure 4 here: https://ipaper.ipapercms.dk/TechMedia/AktuelElektronik/2007/13/?page=6 https://ipaper.ipapercms.dk/TechMedia/AktuelElektronik/2007/13/?page=6. The compensation (roll-off correction in the article) is inserted in the signal chain as shown in figure 3. Figure 2 shows the signals without the compensation. His version is switched in steps while oscilloscope probes use a variable capacitor.
 
 It is told that by putting resistance in series with the speaker the sound is improved. This makes a voltage amplifier act more like a current amplifier.
 
 There is an old B&O speaker with high damping that sounds very good but wastes a lot of power. It requires quite much power just to operate that model at moderate level because of its high damping. I don't know if it is damped by resistance or if it is mechanical damped or both. A good way of driving a speaker is with a current amplifier like used in scopes for their high bandwidth. Of course the output current must be greater for driving a speaker. Current amplifiers can be made quite simple if using matched pairs of transistors and the bandwidth can be something like 40MHZ for standard transistors. This is fast enough to give a very good replication of the finer details of an audio signal.
 
 Regards
 Ole

 
 
 ---In [email protected] mailto:[email protected], <mkjekyll@...> mailto:mkjekyll@... wrote :
 
 Hi Ole,
 Same concept we use when designing a zobel network for a transformer in a mic preamp.  I suppose this magic device sits near the speaker.   I have a hard time believing this would do much with most dynamic speakers as the mechanical impedance and reactance makes a square wave hard to recognize.  On an electrostatic speaker though one can see a pretty good square wave however that is one huge capacitor compared to some trimmer so likely would require a tunable inductor in line with the step up transformer.  Of course I am referring to using a laboratory mic for looking at the square wave not just a probe across the speaker terminals.
 

 On 11/22/2018 11:29 AM, onielsen@... mailto:onielsen@... [EVGRAY] wrote:

   Hi Andreas,
 
 Yahoo doesn't like to transfer the complete messages today even though the delay isn't too great. I completed the message history from the picture and hope it gets through.
 
 To make your own BNC feed through get one male and one female 50 Ohm connector and an inductance free 50 Ohm resistor. Then connect them all in parallel. Instead of one 50 Ohm resistor perhaps use two100 Ohm resistors in parallel. The resistors must be able to dissipate the power at the max voltage across them. With a low impedance current shunt this voltage won't be great. The 50 Ohm feed through must be placed as close as possible to the input of the scope's input amplifier which means the BNC input terminal of the scope.
 
 For high speed oscilloscope probes the inner conductor of the coax cables are made of resistive wire to dissipate energy along the wire. This reduces reflections when the signal reaches the ends of the cable.
 
 I know of a compensation device like used in oscilloscope probes (i.e. like 1:10, 1:20, 1:50, 1:100 etc.). But this device is for audio signals. He tells that when it's correct adjusted the sound picture has depth end everything placed correct. He got the idea from oscilloscope probes where you want to see the signal on the screen like how it is at the probe tip. Never mind how it looks along the signal path as long as the end result is correct. That's what the compensation is for. I.e. when the compensation is correct adjusted an input square wave looks like a square wave on the screen. Without the compensation the corners of the square wave are round. With too much compensation the corners becomes pin shaped.
 
 Regards
 Ole

 
 
 ---In [email protected] mailto:[email protected], <freeen2012@...> mailto:freeen2012@... wrote :
 
 Hi Ole, 
 On 22 Nov 2018, at 18:51, onielsen@... mailto:onielsen@... [EVGRAY] <[email protected] mailto:[email protected]> wrote:
 
 Both ways can be used. For low inductance of a current shunt let the return wire go close to and in parallel with the shunt resistor to minimize any area for the magnetic field.
 
 Here the return wire is twisted around the current shunt.
 
 Also the 50 Ohm feed through is necessary. Without it a lot of reflections will happen unless the scope itself has a 50 Ohm input. As scope inputs usually are 1M Ohm the signal w ill be reflected due to the great impedance mismatch from 50m Ohm to 1M Ohm and the signal will drown in noise. 50m Ohm to 50 Ohm reduces the reflections a lot.
 
 Thanks for the pic (illustrates it well). I already have such a 50 Ohm feed through but never really understood what exactly it does and therefore have never used it. I understand it has an impedance of 50 Ohm like the coax cable to prevent reflexions, yes, but how does it transfer the potential difference to be measured (over the shunt) to the 1M Ohm impedance input of the scope. If we had to build such a 50 Ohm feed through what would we have to do (what is it composed of)? This might help me to understand how it works. 
 
 Thanks a lot,
 

  Andreas

Ole,

As a recording engineer and studio tech I can tell you.  Compression is
used to layer tracks to sound realistic.  If one records drums with the
widest dynamic mics and 24bit PCM the drums do not match the other
instruments as if watching a live show, so compression is properly used
for tracks to sit balanced in the mix.   Unfortunately compression is
mostly abused to create the loudness wars where one CD sounds louder
than another so kids will buy them.   This and the fact most mixes are
now made for earbuds or cars and people are used to a steady noise
level.  It's very sad that with the level of playback available now the
whole industry has regressed. Remember when everyone had large speakers
and a good stereo...  Sadly there are no record men anymore, the AR guys
who would look for talented musicians, most of the music is sampled from
other music and very primitive as musicianship is concerned or lack of
it as could be positively argued.  Like watching re-runs over and over. 
There are some classical recordings with no compression but again the
dynamics are so large it has to be listened to in a quiet room.  How
many people even have a quiet space to listen to music now.

Besides the fact we are at this site and going for a common cause that
could be a paradigm shift I am convinced social media is destroying
civilization. Everything was moving forward until facebook Borged out
everyone.
Kone is a musician and I would speculate he has a similar outlook on the
music scene today vs 70-80s


"


"

Facebook founder Mark Zuckerberg called his first few thousand users
"dumb fucks" for trusting him with their data, published IM transcripts
show. Facebook hasn't disputed the authenticity of the transcript.

The exchange apparently ran like this:

*Zuck*: Yeah so if you ever need info about anyone at Harvard

*Zuck*: Just ask.

*Zuck*: I have over 4,000 emails, pictures, addresses, SNS

*[Redacted Friend's Name]*: What? How'd you manage that one?

*Zuck*: People just submitted it.

*Zuck*: I don't know why.

*Zuck*: They "trust me"

*Zuck*: Dumb fucks

"

On 11/24/2018 12:41 PM, [email protected] [EVGRAY] wrote:
>  
>
> Hi Mick,
>
> "An amp built with super high Q inductor current sources, sounds like
> RF I don't think my tweeters would enjoy that either or the
> transformers in the electrostatics."
> That was just to illustrate that disrupting an inductor behaves more
> like an ideal current source at the moment of opening the circuit.
> Real world current sources usually have a maximum voltage they can
> output. A better example is the Van de Graf generator or some other
> electrostatic generators. The voltage is limited by the load and thus
> always delivers the intended current through that load no matter how
> its impedance changes. Maybe a constant power amplifier is what is
> needed. Such an amplifier delivers the correct power instead of just
> the correct voltage or the correct current. Perhaps that would be a
> good project for good sound reproduction.
>
> "As I said before plug a bass guitar in and that preamp that claims
> flat down two 2 Hz suddenly sounds anemic and weak."
>
> My guess is that the weak point is in converting the electrical energy
> into moving the air. It will be very hard for a loudspeaker membrane
> to complete a good step response. I don't know if the guy with the
> signal compensation measures the sound at the listening position.
> According to the article it is clear to hear when the compensation is
> correct adjusted even though it only has five discrete steps.
>
> There are also amplifiers where a microphone can be attached and a
> test signal is played and used for making the signal processor
> compensate the sound at the listening position. Of course it is at the
> listening position the sound must be correct reproduced. Looking at
> the signal at other points in the signal chain may then show a bad signal.
>
> All this doesn't mean that different individuals may all find the
> sound pleasant. Some may like the sound colored or spiced in some way
> instead of the way the musicians and recording people intended. And
> you're correct much music is compressed. If looking at a VU meter some
> music is recorded at a constant level without much dynamics. This was
> done at the era of CC tape recorders due to the low dynamic range and
> signal to noise ratio. Why it is still done with digital recording
> equipment seems strange! Modern equipment has high dynamic range so
> why isn't it used in many recordings? Anybody know the reason for that?
>
> Regards
> Ole
>
> ---In [email protected], <mkjekyll@...> wrote :
>
> Ole,
>
> An amp built with super high Q inductor current sources, sounds like
> RF I don't think my tweeters would enjoy that either or the
> transformers in the electrostatics.
>
> Her amp is interesting yes, I have spoken to her before and would love
> to hear it, but transformers have their issues too.  Most of the wire
> with gain designers steer clear of transformers for audio as among
> other things they can mess up the fast transient low frequencies due
> to saturation. Tube distortion is a flawed concept from 1950's
> designs.  In fact much of the distortion attributed to tubes is from
> the transformers. Properly designed modern CCS biased tube circuits
> with properly designed cathode follower buffers have as low distortion
> as solid state and less distortion in the factors unmeasured. Solid
> state is like sending music through a rock, tubes do not smear audio
> like rocks because there is nothing in the way of hollow state.  How
> does one measure IM with actual music...  When working with live
> instruments and not smashing everything through compression the
> instantaneous peaks can and do make solid state far more distorted. 
> And it depends on circuit topology as FET's produce more even
> harmonics than do tubes due to their transfer function.
>
> Step response does not provide the full picture but is a good starting
> point.  Sounds waves in real life are going in multiple directions
> sinking and sourcing at the same time, direct and reflected phase
> modulations etc the level of vector analysis would be crazy to know
> what is really happening.  I have heard amps with excellent step
> response almost unmeasurable TIM and Harmonic distortion  that sound
> like crap because as you say all of the components to correlate and
> correct or else some other reason.  When the infinite network analyzer
> is built then we will get much further.  For now audio is still a
> somewhat black art.  When I find problems with a piece of gear someone
> has designed that is often the comeback, "the impulse step response is
> as close to perfect as possible in theory at room temperature".  As I
> said before plug a bass guitar in and that preamp that claims flat
> down two 2 Hz suddenly sounds anemic and weak.
>
> On 11/24/2018 9:08 AM, onielsen@... <mailto:onielsen@...> [EVGRAY] wrote:
>
>>      
>>
>>     Hi Mick,
>>
>>     The current amplifier isn't ideal and as such has limited voltage
>>     swings. The output can't swing further than the supply voltage. A
>>     high Q inductor is closer to an ideal current source when
>>     disrupting the current through it. The voltage may reach high
>>     enough to punch through the insulation of the wire just to keep
>>     the current at the value it had during disconnection.
>>
>>     The problem of amplifiers is also the use of lots of components
>>     in the signal path. Each component has its own resonance
>>     frequency because of not being ideal components. The feedback
>>     loop is for compensating for those errors. One solution to this
>>     is a wire with amplification or next to that an amplifier with a
>>     single stage or active component in the signal path like in the
>>     Zeus amplifier. This is like an old tube amplifier but with a
>>     modern transistor instead of the very distorting tubes (even
>>     though the distorted sound of tubes sound good in human ears).
>>
>>     The Zeus amplifier: http://www.susan-parker.co.uk/zeus.htm
>>
>>     "One of the biggest problems with audio designing is we cant test
>>     what is really going on wideband with music only guess or listen."
>>     Give it a step response by using a square wave as input. If not
>>     coming out as a sharp square wave the signal has changed. Just
>>     look at the oscilloscope probe for how to correct that. It costs
>>     a lot of amplification though.
>>
>>     Regards
>>     Ole
>>
>>
>>     ---In [email protected] <mailto:[email protected]>,
>>     <mkjekyll@...> <mailto:mkjekyll@...> wrote :
>>
>>     Ole,
>>
>>     Yes the current buffer at the output end of the amp decauples the
>>     voltage amp from speaker reactance and is required and the more
>>     current the better all power amps have a basic currrent amp at
>>     the output. Most amp designs are hybrids.  As you say with audio
>>     there are so many octaves and the impedance and reactance are non
>>     linear into a cored inductor, specially one that is a motor also
>>     reacting to air loading modes.  A DC motor will speed up to
>>     destruction with unlimited voltage so what happens when the
>>     impedance goes super high or the speakers are not connected with
>>     an ideal pure CCS amp?
>>     Bass at the lowest impedance needs the most current.  Highs like
>>     fast non slew rate limited voltage.  Wrapping a design in loop
>>     feedback to keep it stable is really not good sounding and lazy
>>     practice but sometimes required. I use a curve tracer to match
>>     parts.  Local degenerative feedback not an issue sonically but
>>     when it's wrapped around a whole circuit looped from out to in,
>>     yuck, at least have the individual parts nested.
>>
>>     One of the biggest problems with audio designing is we cant test
>>     what is really going on wideband with music only guess or
>>     listen.  Something that looks great with pink noise or impulse
>>     responsed can in practice not sound so good.  Why many
>>     afficianados like SET designs because it's just one single ended
>>     tube without all the garbage, while not so good for rock and roll
>>     or stunning dynamics for less bombastic music the imaging can be
>>     superlative.
>>
>>     For audio designs I really think Nelson Pass is solid, big
>>     respect here.  In pro audio we like a shitload more watts on
>>     standby as every extra frequency divides power but for home gear
>>     can't go wrong with Nelsons designs and they are cheap and fun to
>>     build.
>>     http://www.firstwatt.com/faq.html
>>
>>     Also a really good sound resource is Rod Elliot
>>     http://sound.whsites.net/index2.html
>>
>>     This article goes into some of what we are talking about:
>>     http://sound.whsites.net/project56.htm
>>
>>
>>     On 11/24/2018 4:18 AM, onielsen@... <mailto:onielsen@...>
>>     [EVGRAY] wrote:
>>
>>>          
>>>
>>>         Hi  Mick,
>>>
>>>         The person here: http://nov79.com/amr/cont.htm claims that
>>>         current amplifiers are the best way to drive speakers.
>>>         Citing from page two:
>>>         "The current amplifier drives the speakers. It has no effect
>>>         upon the signal. It is the perfect black box which allows
>>>         the voltage amplifier to drive a heavy load as if it were no
>>>         load at all."
>>>
>>>         The only problem is for mass production as the two PNP
>>>         transistors and the two NPN transistors must be matched. For
>>>         low signal the solution is buying the transistors as IC
>>>         packages as they're matched by using the same crystal for
>>>         all four transistors. The person describes three sizes of
>>>         amplifiers.
>>>
>>>         This could be used for making a cheap differential probe or
>>>         current probe amplifier for scopes. The conventional ones
>>>         are pretty expensive to buy.
>>>
>>>         "Audio is a weird duck as to an RF engineer it looks like
>>>         but a small notch however there are some really big
>>>         differentials in that small window concerning how materials
>>>         react likely having to do with the long wavelengths and the
>>>         (phase?) change around 10kHz where radio emission begins."
>>>         To cover the hearing range of human ears the amplifier has
>>>         to cover around seven octaves. That's pretty much. A human
>>>         eye sees only one octave. A RF transmitter may be even more
>>>         limited.
>>>
>>>         Regards
>>>         Ole
>>>
>>>
>>>
>>>         ---In [email protected]
>>>         <mailto:[email protected]>, <mkjekyll@...>
>>>         <mailto:mkjekyll@...> wrote :
>>>
>>>         Ole,
>>>
>>>         Current amplifiers are not a really a good choice to drive
>>>         speakers anyways as high impedance will get more and more
>>>         voltage with a CCS.  Better to use voltage amps biased with
>>>         current sources.  Dynamic speakers present a varying
>>>         impedance bandwidth so tweeters will begin to clip,  unless
>>>         the speakers are electrostatic where the impedance rises as
>>>         freq drops inverse to dynamics.  Current amps are a good
>>>         choice for some preamp circuits though which are driving a
>>>         less reactive much more constant impedance and as you claim
>>>         can then leverage the bandwidth of transistors.  I am having
>>>         an issue with a current pre design right now that has huge
>>>         bandwidth on the bench.   On a scope impulse response is
>>>         flat from several Hz to almost a mHz however when used for
>>>         recording real world signals rather than a sweep the low end
>>>         is much thinner sounding than it should be.  I will try a
>>>         diff power supply to see if massive current reserves will
>>>         make a difference.
>>>
>>>         Thanks for the probe link, I will read in a bit.
>>>
>>>         Interesting enough that audio is normally considered to low
>>>         freq for skin effect to matter as most RF engineers will
>>>         attest but silver plated oxygen free copper makes a big
>>>         difference in sound quality.   The old fashioned wire wrap
>>>         is often very good for audio as it is silver plated copper
>>>         and very thin and very inexpensive.   Good way to make
>>>         interconnects that rival those expensive ones for a few
>>>         bucks.  Coax is not really good for audio either as presents
>>>         too many non linearities.  Audio is a weird duck as to an RF
>>>         engineer it looks like but a small notch however there are
>>>         some really big differentials in that small window
>>>         concerning how materials react likely having to do with the
>>>         long wavelengths and the (phase?) change around 10kHz where
>>>         radio emission begins.  I imagine you can explain this much
>>>         better than I just did and I don't know the proper
>>>         terminology of where AF starts becoming RF which is much
>>>         lower then the formal claim of about 100kHz.
>>>
>>>         ...
>>
>