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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 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 http://www.firstwatt.com/faq.html
Also a really good sound resource is Rod Elliot
http://sound.whsites.net/index2.html http://sound.whsites.net/index2.html
This article goes into some of what we are talking about:
http://sound.whsites.net/project56.htm 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 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.
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