Thank you for your answer.
I think that if I were to take the same circuit as in our most recent power amplifier and run it in pure class A (it would probably need fan cooling) that the THD would be at least an order of magnitude lower at 100 watts. Then it would be trivial to unbalance some part of the circuit to increase the measured THD (virtually only second harmonic) without affecting anything else.
From your answer, the increase in THD in such a scenario would be inaudible.
I agree, and that is the point I was trying to make. Thank you for helping me to clarify it.
Fortunately , amp designers haven t to answer this question as it has
already its reponse through the amp s environement.
What is to consider is the THD of the source, say a CD player.
Since its claimed SN/N ratio is at 96db, it is a minimum for an amp
of good quality to equal or better, best this number by a few db.
-100db level THD at the listening level you quote (2.5W) seems quite
reasonnable given the state of the technology.
Of course, the speakers will distort much more, but it s not an
excuse to be negligent in the amplification stage.
That said, since you do not use NFB, such THD ratios seems
difficult to catch, thus the rethoric questionning the validity
of the THD audibility.
Charles, decreasing the lf olg with a resistor (that was the issue) doesn't do anything to inprove other amplifier performance points. It does increase ol bw but that's hardly a performance point in itself.
But Cdom decreases the ol gain by turning it into increased fb around the Vas, leading to lower Vas distortion. That DOES increase amplifier performance.
It doesn't operate in two different ways. The inflection is the result of increasing fb at lower freqs resulting at lowering distortion as freq gets lower, until the vanishing distortion disappears in the amp noise. From there on, distortion remains flat to even lower freqs. I don't see how that can be worse compared with an amp where the distortion remains as high as at hi freqs even at low freqs. I'm not saying it improves audible performance, that depends on other issues as well, but it certainly doesn't make it worse.
jan didden
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Many opinions are presented, the most useful one, (to me) is the problem of the 'inflection point' within the audio band due to the open loop gain bandwidth being in the audio band. I agree that this a serious potential problem and probably the 'Achilles Heel' of my Parasound designs. However, I think that it is some aspect of FM or PIM distortion that is generated by the fall in open loop bandwidth that makes the most difference.
Regarding PIM, Gm variation with amplitude and resulting corner frequency modulation is the issue.
Yes, both are important. However, in a 'perfect world' I would prefer an open loop bandwidth greater than 20KHz, with or without feedback. This would minimize the possibility of PIM distortion AND give a constant characteristic with frequency of the distortion reduction with feedback. What concerns me most, is NOT what we CAN measure, but what we CANNOT measure, yet the ear appears to hear the difference. Both Charles Hansen and I have made world class preamps that use NO global loop feedback. Charles and I agree that this is the best way to go, and we have proven this, at least to the satisfaction of our clients, that this is so. Where Charles and I somewhat differ, for practical reasons, as much as anything, is having no negative feedback with power amplifiers. However, I have heard too many open loop power amplifiers that sound better than my best efforts, to my own ears, that I have to concede that open loop operation with power amps is probably still best, IF everything else is done to the highest quality. The ONLY reason that I can think of, at this time, is the generation of PIM distortion when the open loop bandwidth falls below 20KHz.
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Charles, since you design amplifiers with no negative feedback: what are the advantages of NFB-less amps compared to the traditional high NFB ones ? By advantages, I mean sound-wise (not measurement-wise).
How would you describe the sound of your own no NFB amps. compared to traditional high NFB ones ? What are the main improvements in sound ?
Others' input is welcome.
How would you describe the sound of your own no NFB amps. compared to traditional high NFB ones ? What are the main improvements in sound ?
Others' input is welcome.
To me the sound of zero-feedback is more natural and more convincing. It is less about sound and more about music.
The first solid-state power amp I ever heard of with zero feedback was the Wingate, designed and sold by (I believe) Steve Wingate. It was reviewed very positively in TAS, but only sold direct. The company folded within a year, as do most direct-sales operations. I didn't know it at the time, but he patented his circuit. So you can go online and see his circuit. Much better than most construction projects I see. If you're bored you might build one of his amps and see what zero-feedback sounds like.
But it won't make as much difference until that last piece in the playback chain becomes zero-feedback. So you have to also make a zero-feedback source and preamp. Obviously the recording was made with feedback. I can't explain why this doesn't mess up the sound. Or maybe it does. Maybe if a record company had a fully zero-feedback recording chain we would all faint with pleasure when we heard the results.
Thanks Charles.
For any one interested...............
Audio power amplifier - Google Patent Search
Jam
For any one interested...............
Audio power amplifier - Google Patent Search
Jam
>But it won't make as much difference until that last piece
>in the playback chain becomes zero-feedback.
>So you have to also make a zero-feedback source and preamp.
>Obviously the recording was made with feedback.
>I can't explain why this doesn't mess up the sound.
It doesn't work that way. One distortion will not
mask another. It's often said in the context of
op-amps that why bother not using them since
they are in the recording chain.
BUT ......
If 11 op-amps are put in series, the percieved
signal degradation between the output of
#10 and #11 is the same as between 0 and #1 .....
>in the playback chain becomes zero-feedback.
>So you have to also make a zero-feedback source and preamp.
>Obviously the recording was made with feedback.
>I can't explain why this doesn't mess up the sound.
It doesn't work that way. One distortion will not
mask another. It's often said in the context of
op-amps that why bother not using them since
they are in the recording chain.
BUT ......
If 11 op-amps are put in series, the percieved
signal degradation between the output of
#10 and #11 is the same as between 0 and #1 .....
I'm not at all interested in criticizing people for the degree they have, or any other personal issues. If you read me carefully, I criticize claims and arguments, not personalities.
Where did you find my record - just curious?
I've never taken issue with that, and never will. Its entirely tangential to the claims and arguments you make on this thread.
Yet you attribute to him things he would never claim for himself - that he 'has all the answers'. I took that to be mocking him and it appears this impression isn't limited to just me.
This 'holy grail' is entirely your gloss Charles, to me its hilarious that you would speak of the man in such hushed tones.
Yes, I am sure that DS disagrees with you. Notice you've changed the words I actually used to suit your point😀
If you're speaking of psycho-acoustic effects, then please pardon this interruption.
If not... A common problem in various RF systems is what happens when imperfect system elements are cascaded. Rather than take up space on something that might not be part of the discussion, I suggest Googling (Binging??):
spectral regrowth
and
CSO cascade
Especially for the first there are loads of papers, many as published in refereed engineering journals, discussing the subjects in sleep-inducing detail. Since even broadband RF systems are small in terms of the bandwidth they operate over compared to audio, in octaves, many of the same principles apply I believe. Look at pages 502 & 503 of Bob Cordell's new book.
HUH???
Increasing OL bandwidth is nothing???
Since when?
If you like the sound of more feedback, then I guess so. Or if you judge your amplifiers with a meter instead of listening, then you are absolutely right. At low frequencies, anyway.
Maybe "two different ways" wasn't the best way to describe it. But the amp will certainly sound "two different ways" at high frequencies and low frequencies. At low frequencies there will be a lot of feedback around the entire circuit, including the output stage. At high frequencies there will be a lot of feedback around one stupid little transistor, and the major source of distortion (the output stage) will have much less feedback.
Of course it will sound "two different ways"!
Interesting here that you've misread Bob Cordell, myself and now Jan. This is really fun😀
Jan is not saying that increasing OL bandwidth is nothing. He's saying that increasing OL bandwidth by VAS resistive loading is nothing. Big difference.
Only according to you does feedback have a sound. But since you have put up not one iota of listening evidence in support of that sweeping generalisation, Jan would be entirely reasonable to ignore it.
In might be important to note why VIDEO amplifiers have high open loop bandwidth with similar circuitry as audio amplifiers that are slightly configured to have higher feedback at low frequencies. WHAT is the video circuit sensitive to?
>If you're speaking of psycho-acoustic effects,
Yes ..... ' aural impressions '
Have you ever tried the experiment "
Aurally ?
>then please pardon this interruption.
You are pardoned 🙂
Yes ..... ' aural impressions '
Have you ever tried the experiment "
Aurally ?
>then please pardon this interruption.
You are pardoned 🙂
I thought you might talking about psycho-acoustics, but obviously wasn't sure.
The distortion generation subject still holds though...
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