Tony and I have had introductions...he recently sold me a faceplate for an 800 that was damaged by FedEx. Very nice guy. I know they will service it for me but do you think he would give me some tips over the phone as to what the problem might be? That would be great, I really enjoy fixing stuff myself.
Mr. Curl,
Are there any threads you are involved with that talk about tweaks to the HCA series of amps? I actually own five different models, I kinda collect them. It would be interesting to hear what you would do to these units yourself if you were to do any upgrade/tweaking of you own. I don't want to hijack this thread but I would love to know what areas of the circuit would be optimized if production costs were not an issue.
Thanks for you help, it's a real honor to actually be conversing with the guy who designed one of my favorite series of amps.
Sincerely,
Jeff
Mr. Curl,
Are there any threads you are involved with that talk about tweaks to the HCA series of amps? I actually own five different models, I kinda collect them. It would be interesting to hear what you would do to these units yourself if you were to do any upgrade/tweaking of you own. I don't want to hijack this thread but I would love to know what areas of the circuit would be optimized if production costs were not an issue.
Thanks for you help, it's a real honor to actually be conversing with the guy who designed one of my favorite series of amps.
Sincerely,
Jeff
I strongly recommend that you read Cheever's thesis for yourself. Not because it contains any truths but because it is an excellent example of badly flawed logic on many accounts. It comes to the wrong conclusions for the wrong reasons. The entire approach is wrong. It isn't even a paper about electrical engineering. And it goes to prove that credentials alone are meaningless. They do not prove expertise or competence.
Here first is the gist of his thesis. Anyone who has read it should feel free to correct any mistakes or give different interpretations to this account of it.
Cheevers invited some friends to listen to some audio equipment. He played several amplifiers and found that his friends preferred those whose measurements were not so hot over those which looked far better on paper or on a lab test bench. I think the one they liked best was Carey, the one they liked least was Threshold. He set about to find out why. The rest of the paper argues that the critical difference between them was in the nature of harmonic distortion they produced. The ones they liked best had a higher percentage of spurious lower harmonic components in its distortion makeup, the ones they liked least had a higher percentage of higher harmonic components. Conclusion, amplifiers with a higher percentage of lower harmonics in its distortion components sound better. He also tried if I recall to create a weighting factor, a figure of merit which took this into account. This was the original statement here that brought this topic up.
Mr. Curl, perhaps you don't remember that you were so impressed by this paper several years ago that you lauded it but I read it and I found it to be tripe unworthy of an engineer even at the bachelor's level. Its deplorable flaws are typical of the audiophile mentality, not of the far more trained and disciplined engineering mentality.
jmillerdoc, contact Tony with your problems. He even fixes MY amps, on occasion.
As far as tweaks for the Halo series of power amps, there are really none that I do. Some of the older designs can be upgraded with LESS but better, power supply bypass caps. There are professional modifiers out there who do this sort of thing, however, I don't. It is just too difficult for me with my vision problems to do anything very useful, myself, and techs are VERY EXPENSIVE and cut into my income seriously, if I attempt to use them for this sort of thing. I miss the good old days, when I could putter around in my lab on my own, happy with the results.
As far as tweaks for the Halo series of power amps, there are really none that I do. Some of the older designs can be upgraded with LESS but better, power supply bypass caps. There are professional modifiers out there who do this sort of thing, however, I don't. It is just too difficult for me with my vision problems to do anything very useful, myself, and techs are VERY EXPENSIVE and cut into my income seriously, if I attempt to use them for this sort of thing. I miss the good old days, when I could putter around in my lab on my own, happy with the results.
The harmonic masking work goes back at least as far as 1924 and the paper by Wegel and Lane "The theory of auditory masking by on pure tone by another tone and it's probable relation toot the dynamics of the inner ear." (sorry, don't have a link). That work was followed up in studies over several decades.
Not all amplifiers can be characterized by their harmonic content, but many can. It's really not news.
Not all amplifiers can be characterized by their harmonic content, but many can. It's really not news.
I followed your advice and re-read the paper. I could not
find the event you mention, and Threshold is not
mentioned anywhere I could see. Perhaps you would care
to be more accurate when being so critical.
Soundminded - Thanks, yes I read the paper and came to the same understanding as you, that Cheever compared two only amplifiers (Cary 300SEI and Bryston 3B-ST), measured the distortions and concluded that higher order distortion harmonics are disproportionately injurious to sound compared to lower order distortion harmonics.
To this he adds discussion of human ear distortion behaviour and amplifier overload behaviour.
With this set of input information he attempts to define an amplifier figure of merit....as far as I understand his method is essentially correct and nothing new (as Pano suggests).
As I see it the only question is that of his weighting factors....with measurement and subjective evaluation of a greater range of amplifiers this harmonics weighting curve could be refined and amplifier weighted harmonics measurement be more reasonably indicative of amplifier subjective performance than standard simple distortion measurement methods.
I still don't understand the holes in his discussion ?.
Eric.
To this he adds discussion of human ear distortion behaviour and amplifier overload behaviour.
With this set of input information he attempts to define an amplifier figure of merit....as far as I understand his method is essentially correct and nothing new (as Pano suggests).
As I see it the only question is that of his weighting factors....with measurement and subjective evaluation of a greater range of amplifiers this harmonics weighting curve could be refined and amplifier weighted harmonics measurement be more reasonably indicative of amplifier subjective performance than standard simple distortion measurement methods.
I still don't understand the holes in his discussion ?.
Eric.
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On pages 2 through 5 Cheever compares A Carey CAD300SEI with a Bryston 3B-ST as quintessential examples of the extremes he uses to make his point.
At the bottom of 31 and continued on 32;
"There has been a failure in the attempt to use specifications to characterize the subtleties of sonic performance. Amplifiers with similar measurements are not equal, and products with higher power, wider bandwidth, and lower distortion do not necessarily sound better. For a long time there has been faith in the technical community that eventually some objective analysis would reconcile critical listeners subjective experience with laboratory measurement. Maximum intrinsic linearity is desired. This is the performance of the gain stages before feedback is applied. Experience suggests that feedback is a subtractive process; it removes distortion from the signal, but apparently some information as well. In many older designs, poor intrinsic linearity has been corrected out by large application
of feedback, resulting in loss of warmth, space, and detail. 18, [25]"
18 A quote by Nelson Pass, President of Pass Laboratories, from the Passlabs.com website. Mr. Pass is one of the most prolific inventors in audio. He designed all the Threshold and Phase Linear line. Pass Laboratories specializes in large MOSFET based single-ended audio amplifiers and pre-amplifiers.
Sorry if I put you in the wrong camp Mr. Pass. I don't keep much track of the players, I don't keep many scorecards lately.
Compare this with the first statement Dr. Phair made at the outset of the course on feedback systems I took as a senior in college in the fall of 1968. "Negative feedback is the single most important development in electrical engineering since the second world war." I think a good argument could be made for that assertion today. Every industrial control system I know of depends on it. I also think it was about the toughest course I ever studied. The textbook I used has hundreds if not thousands of intergral and differential equations modeling feedback control. The misapplication of this most powerful tool by oversimplifying it is one of the surest ways to disaster. Those who do not apply it skillfully can create not only more distortion than they intend to cure but wreck havoc. In the worst case, they'll unwittingly be building an oscillator. To condemn negative feedback unconditionally without reservation because so many who use it don't have the skill to apply it artfully is to dismiss this most important technique. However, if they can't master it, those who design circuits which would benefit from it should definitely stay away from it.
BTW, this still does not address the flaws I find in Cheever's thesis which are based on the way the argument was constructed.
He must have meant the first world war.
The problem is, there hasn't been an effective theory about
what sounds good. Somewhere in the 70's or 80's the
objective technology became good enough that high end
audio became a post-modern enterprise, catering to the
idiosyncrasies of the neural networks between our ears.
He must have meant the first world war.
Nelson,
"Negative feedback is the single most important development in electrical engineering since the second world war."
I thought he was claiming the Second World War as the more important development that electrical engineers have done, even more important than Negative Feedback.
Best Regards,
TerryO
Nelson, this is rediculous. Neither Cary nor Bryston cut the mustard here against your offerings. Soundminded is out of his mind. As far as i can tell you could design a poweramp with extremely low distortion if you whould ever decide to do so. To use your name as a vehicle to disregard any efford that tries to advance the soundquality of amplifiers is ........
Nelson and JC are Both Correct...
Soundminded (ok so what is your real moniker ?), agreed that NFB techniques in control systems are monstrously important and typically complex.
Agreed that NFB techniques in audio are important, however audio is an electronics niche subject where signals are unusually complex in nature, and prone to electronic and acoustic distortions that are critically evident when measured (listened to) by the human ear, and to add to that the ear has a constant reference criterion....i.e. natural sounds surrounding us constantly.
I did not distil that Cheever condemned NFB per se, however he is illuminating that NFB techniques can cause THD and IM products that are discordantly unnatural sounding, and that overload behaviour and overload recovery behaviour is further critical to subjective acceptable listening.
Eric.
Soundminded (ok so what is your real moniker ?), agreed that NFB techniques in control systems are monstrously important and typically complex.
Agreed that NFB techniques in audio are important, however audio is an electronics niche subject where signals are unusually complex in nature, and prone to electronic and acoustic distortions that are critically evident when measured (listened to) by the human ear, and to add to that the ear has a constant reference criterion....i.e. natural sounds surrounding us constantly.
I did not distil that Cheever condemned NFB per se, however he is illuminating that NFB techniques can cause THD and IM products that are discordantly unnatural sounding, and that overload behaviour and overload recovery behaviour is further critical to subjective acceptable listening.
Please elaborate...what are the flaws in the way that Cheeve'rs argument is constructed ?.
Eric.
Audio signals are not nearly so complex. Bandwidth in less than 1/300th of an NTSC TV signal. Dynamic range although logarithmic has at most 1000 discernable distinct levels even if you believe you can hear increments of 1/10 db the way JA claims he can. Many signals in scientific research are far more difficult, far more complex, and far more important. None of them garners the lunacy among those who depend on them for a living that audio circuits have among audiophiles.
Cheever tied negative feedback to distribution of distortion products he condemns implicitly if not explicitly. This condemnation is why he put it inm his paper in the first place. This distribution may be because in the circuits used, it is more effective at canceling distortion at lower frequencies. This is a guess, he never bothered to find even that out.
I'll post my criticisms of Cheever later. I want to see if Nelson Pass has a comment about Cheever's paper first.
Cheever tied negative feedback to distribution of distortion products he condemns implicitly if not explicitly. This condemnation is why he put it inm his paper in the first place. This distribution may be because in the circuits used, it is more effective at canceling distortion at lower frequencies. This is a guess, he never bothered to find even that out.
I'll post my criticisms of Cheever later. I want to see if Nelson Pass has a comment about Cheever's paper first.
He must have meant the first world war.
The problem is, there hasn't been an effective theory about
what sounds good. Somewhere in the 70's or 80's the
objective technology became good enough that high end
audio became a post-modern enterprise, catering to the
idiosyncrasies of the neural networks between our ears.
The "sounds good" theory of high fidelity sound reproduction of music is of course one of the most obvious traps in judging the relative merits and capabilities of equipment but it is the one audiophiles fall for most. So by that theory, if one amplifier distorts a signal thereby masking other distortions inherent in it, it is superior to one which reproduces the distorted signal accurately even though it is less pleasing to listen to. If the sound of a buzz saw is reduced to sounding like an electric toothbrush under a pillow because that's how the amplifier distorted it, that makes it a better amplifier? As an audio amplifier is a purely electrical device, I am surprised that anyone would use this marketing ploy unless they acknowledge that they cannot sell accuracy at a comparable profit. I agree that the methods most commonly used to measure audio amplifiers do not accurately indicate their relative strengths and weaknesses in this era the way these methods once did. IMO that is because the measuring methods do not reflect the way they are used in the real world.
Subjectivity is a major feature of the high end audio
landscape. As I said, the difficulty is entirely between the
ears, and if you read much of the literature of cognitive
psychology you have to conclude that it is hideously
complex and not well understood, not to mention varying
dramatically between individuals.
Sixty years ago or so, measurements corresponded better
with subjective opinion, but I think that was because the
equipment didn't measure very well. Now it generally
measures very well, and the objective technical problems
are largely solved.
To paraphrase McLuhan, we take our mature technologies
and turn them into art.
OK, I'll stop stirring the pot...
landscape. As I said, the difficulty is entirely between the
ears, and if you read much of the literature of cognitive
psychology you have to conclude that it is hideously
complex and not well understood, not to mention varying
dramatically between individuals.
Sixty years ago or so, measurements corresponded better
with subjective opinion, but I think that was because the
equipment didn't measure very well. Now it generally
measures very well, and the objective technical problems
are largely solved.
To paraphrase McLuhan, we take our mature technologies
and turn them into art.
OK, I'll stop stirring the pot...
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