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Old 23rd December 2011, 07:42 PM   #31
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Well Thorsten, you fight the 'good' fight. I am not able to, unfortunately. I am NOT for deliberately added distortion, but 2'nd harmonic has been shown to be tolerable to quite high levels, throughout the history of audio reproduction. Even 3'rd harmonic is reasonably tolerable until you get above 3% or so, maybe even more on peaks. This was proven for about 50 years with analog master tape recording that produces 3'd harmonic almost exclusively. It always amazed us as to how good we could make solid state electronics, YET the loudspeakers and the sources, typically analog tape or vinyl records, had so much higher distortion. How could making 'better' electronics make any difference at all? Because we could still hear the differences. This is why, Bascom King, another engineer, and I went to see Richard Heyser at his home, about 40 years ago. Richard told us that it was 'negative feedback' OMG! That made the difference. He said that he proved it more than a decade earlier with a power amp design that he made for JPL, allegedly to go to the Moon. There is an AES preprint of this amp design in the AES archives. Talk about a crazy design. We should make it up and try it, ourselves. Looks like something like Nelson Pass might make as a joke. He said that he just tried it on his K-horn for the heck of it, and found that it sounded better than anything else he had around. HE pinned it down to 'negative feedback', I didn't. I just know from experience that he was on the right track.
For the record, Bascom King designed the major power amp that recently got ' Power Amplifier of the year' in TAS, which is based on a unique design of his that he discussed with me, some 40 years ago.
He, Peter Madnick and I (by designing the JC-80 that it was based on), produced the preamp that got the 'Preamp of the year' award in the same issue of TAS, Jan. 2012
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Old 23rd December 2011, 07:57 PM   #32
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The fact is that "zero distortion" is not possible. So "low" and "high" must be seen with a point of reference.
Not physically possible. That doesn't prevent zero from being a reference.
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Earl Geddes once posted four tracks of music. One had been subjected to a process that produced 0.1% THD, the second to one that produced 9.6% THD and the third produced 12.6%.
Mr. Geddes has probably forgotten more about electroacoustics than I'll ever know. I can only search for that thread and meagerly attempt to figure out what was happening.
If your question is "does this device have 1) audible distortions and 2) objectionable distortions" I would say if reproduction accuracy is the goal, the context, if you will, then audible distortions, whether objectionable or not, are reproduction inaccuracies. Calling (or perceiving) a distortion pleasant/spacious/warm/alive/whatever doesn't make it any less inaccurate.
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Old 23rd December 2011, 08:04 PM   #33
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R. Heyser's paper is: 'A Signal Biasing Output Transformerless Transistor Power Amplifier' AES Oct. 5-9, 1959 Preprint 91 Check it out! Especially Nelson Pass!
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Old 23rd December 2011, 09:02 PM   #34
Francec is offline Francec  Australia
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He has as much right to state his view as those in this forum who, unequivocally, state that a form of interconnect can alter the behaviour of individual electrons flowing through it.

Yes, this is sarcasm and yes, I am amused by the new branches of physics which are, seemingly, discovered, almost daily, in these forums.

I also apologise to all of those mathematicians, scientists and engineers who toil daily in the misguided belief that they are actually contributing something to human knowledge when it is quite clear that all you need is self-belief and no knowledge whatsoever.

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Old 23rd December 2011, 09:13 PM   #35
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Originally Posted by ThorstenL
If an amplifier with low measured THD sounds bad according to listeners it sounds bad. If one with high measured THD sounds good according to listeners it is good. Yet our technocratic elite here at DIYA will insist that the second item is "bad" and the first is "good".
This argument technique is called "attacking a straw man".

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So, in one case 0.1% THD is too much and in another 9.6% is inaudible, which tells us what precisely?
We should design our equipment to give precisely 9.6% THD at maximum output? (or normal listening level?)
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Old 23rd December 2011, 09:14 PM   #36
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Originally Posted by SY View Post
Perhaps you might not be able to, but most competent engineers could. If you can see it on a scope, it will cause a difference in the frequency spectrum.
SY this is a borderline post IMO insinuations of incompetence. Please tone it down a little

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Old 23rd December 2011, 09:19 PM   #37
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Originally Posted by DF96 View Post
A half-wave pulse has infinite bandwidth (although finite slew rate), so all (finite-bandwidth) amps will modify it in some way. Testing audio amps with a non-audio test signal is of course an interesting exercise, but you then have to try to read across to how the amp will behave with an audio signal.

"frequency compression in the initial wavefront": this is mixing frequency and time domain descriptions. Could you show us some of your results? My guess is that most of what you are seeing is simply low-pass filtering, but the phase response around the roll-off point could have some effect. The really interesting part would be any residual non-linear effects, as you surmise.
Quite right, but I am looking for SOMETHING I can point to that is a repeatable test to show there is a difference in the transfer function. I don't have a way to capture this in a picture yet as I was using an analog scope. I only described what I saw, not what seemed to cause it. I will get back to this after I play with the Hexfred diodes I ordered and "fresh" caps for some of my 30 year old amps, and oh yea, I am in the middle of another set of speakers to optimize. This would be easy if I did not have to work for a living too.

With all due respect to the current amp designers, why do my old Rotel RA-840 and RB-941's pass my wife's critical ear and a lot of it's contemporaries do not? Failing are amps from Adcom, Parasound, Nad, Hafler, Aimor, and B&K. My Creek seems OK. None of these were considered slouches! If I can remember back that far, she passed the Aaragon and a small Krell but they were out of my price range. I would love to try a Naim, Linn, Cambridge, Music Fidelity,or a Bryston but alas, not even close for used one but I keep bidding.
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Old 23rd December 2011, 09:26 PM   #38
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Which Parasound? Maybe I can find the reason.
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Old 23rd December 2011, 09:28 PM   #39
SY is offline SY  United States
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Originally Posted by tvrgeek View Post
With all due respect to the current amp designers, why do my old Rotel RA-840 and RB-941's pass my wife's critical ear and a lot of it's contemporaries do not?
It may have nothing to do with the amps themselves. What you want to do (if you're really interested in nailing it down) is to have her do a rigorously level-matched comparison (that means within 0.1dB), at levels under clipping, without YOU (as well as her) knowing which amp is switched in when. Double blind is particularly critical with married people- see my favorite anecdote in the last issue of Linear Audio.

If she can distinguish them then, you have a valuable asset on your hands which you can probably monetize.
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Old 23rd December 2011, 09:35 PM   #40
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Just give me the Parasound model, then if you can, the subjective complaint from your wife. This is how I learn and grow, not the way some others do.
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