john curl said:I hope that anyone in competition with me in the audio marketplace will use as much negative feedback as they can get into a design.
They will use it well, and wisely, and they will probably also use MOSFETs well and wisely.
Oh, wait a minute! They already have! Read some amplifier reviews. The Halcro has gotten far more rave reviews than the JC-1. Stereophile picked it as their amplifier of the year. I don't recall seeing them pick the JC-1. Halcro is not the only competitor that uses feedback wisely to compete with you, John. Boulder is but one other example.
The JC-1 is an excellent amplifier, and it has been well-received, but it is by no means alone amongst many amplifiers that use negative feedback.
Bob
janneman said:
I believe there are errors in Cheever's paper, but I don't recall
that being one of them. Now that you have a copy, you would
be able to correct my memory.
In any case, since Cheever is apparently reproducing some of
Baxandall's work, perhaps it is best to refer to the original. The
subject came up here because somebody mentioned that
negative feedback alters the spectrum of distortion and provided
a curve showing an example.
The argument will go on and on as long as there is a discrepancy
between measurement and subjective judgement. The neural
networks that process audio are subtle and poorly understood.
The argument is often put forth that subjectivists like their
distortion, and that the distortion they like is 2nd harmonic. This
is a red herring. Just about everybody I know prefers low
distortion in actual listening, but their ears appear to care how
the low distortion was achieved, in addition to all the other things
like the color of the lights and the thickness of the faceplate.
This is the entertainment industry, and as such it is also a fashion
industry. The digital amps, the chip amps, the SETs and the
Halcros all get their day in the sun, and some go on to be classics,
none based on their distortion spec as far as I can tell.
Nevertheless, I believe that intrinsic linearity in each component
device is the best approach. If you apply feedback or error
correction without having done all you can to minimze distortion
in the first place, then that is a compromise.
Not that there's anything wrong with that...
Nelson,
I can only agree to your post above. The issue on the change of harmonic structure with feedback is a technical discussion trying to explain that going from zero feedback to some other number doesn't automagically mean that the distortion would decrease in step. That is something that can be analysed, measured etc which in my book is a Good Thing. It's always good that you know what's going on in your circuits.
How that relates to audibility is another kettle of fish. That is almost impossible to couple to technical issues because audibility judgements and reports are almost 100% anecdotal, highly personal and limited to a specific instance in space and time.
As you yourself noted, and I can only wholehartedly agree, the sound vibrations getting into your ear are only one of many factors that determine the sound experience. I have started to document some of that on my website but the subject is huge and you roll from one surprise into another.
In another post I ventured the idea that hi-fi (by whatever definition) is possibly going around in circles instead of making real identifiable progress. Your last but one para is in line with that idea.
Jan Didden
PS I'll take a look again at that Cheever paper in the next few days.
I can only agree to your post above. The issue on the change of harmonic structure with feedback is a technical discussion trying to explain that going from zero feedback to some other number doesn't automagically mean that the distortion would decrease in step. That is something that can be analysed, measured etc which in my book is a Good Thing. It's always good that you know what's going on in your circuits.
How that relates to audibility is another kettle of fish. That is almost impossible to couple to technical issues because audibility judgements and reports are almost 100% anecdotal, highly personal and limited to a specific instance in space and time.
As you yourself noted, and I can only wholehartedly agree, the sound vibrations getting into your ear are only one of many factors that determine the sound experience. I have started to document some of that on my website but the subject is huge and you roll from one surprise into another.
In another post I ventured the idea that hi-fi (by whatever definition) is possibly going around in circles instead of making real identifiable progress. Your last but one para is in line with that idea.
Jan Didden
PS I'll take a look again at that Cheever paper in the next few days.
Nelson Pass said:
Well, that's fashion for you. I do believe in progress, but it
looks like we'll get there helically.
Reminds me of the pilgrimage (sp?) of devout catholics from the French Pyrrenees to Santiago de Compostela in northern Spain. If you want to do it right, you take three steps forward followed by two steps backwards. And preferably on your knees...
Some pilgrims get so fatigued that they confuse the numbers and actually start to take two steps forward followed by three steps backwards. Maybe audio is a bit fatigued once in a while as well..
Jan Didden
john curl said:
The JC-1 is a very good amplifier, designed by someone who is not a big fan of negative feedback. I'm interested to know.
Why are you dodging a simple question like this? Is it a trade secret, or are you concerned that the actual numbers you use will conflict with what you have said about negative feedback?
Presumably, those numbers would correspond to your definition of a low-feedback amplifier. I'm interested to know what that is.
C'mon, stand up and be counted.
Besides, you can always fall back on the "THX made me do it" excuse.
Bob
(waves hand frantically) Ooooh! Ooooh! Oooooh! Mistah Kottah!
I'm pretty stupid about transistors, but in tube amps, it's well known that increasing feedback can very badly deteriorate overload performance. The amp clips, so the feedback drops. This makes the clipping worse, and we're now on Nelson's helix, rapidly dropping sound quality down the toilet.
OK, I will tell you. IF I wanted significantly lower distortion, I would have to better match the VAS complementary fets, either by using different fets, cascoding, or going back to bipolar transistors. I would have more global feedback, and much lower 2'nd harmonic, which is only there, because the Vmosfets are such a lousy match to each other.
Is it worth it? I doubt it, because I can assure you that I WOULD find a greater proportion of 7th harmonic in the low level distortion. This is what I care about. This would also lower my open loop bandwidth as well.
Is it worth it? I doubt it, because I can assure you that I WOULD find a greater proportion of 7th harmonic in the low level distortion. This is what I care about. This would also lower my open loop bandwidth as well.
John,
Your post #1101 - I am going to save screen space by not quoting.
I have replied to you before regarding years of experience and "world fame" - let us leave it at that; your memory is short. (And you don't want to push "world fame" as a norm now ... might land you in some really funny company.) Let us just say I have also had me modest moments, but I have never found personal fame used as scientific proof, not even by Einstein. And as for (automatically?) denigrating the hearing of those who do not agree with you ... that was unworthy of you. Seems some of us honestly want to get to the truth, others only to win an argument.
When you use quality of foodstuffs or whatever as an example, we are not on the same page. I (and the whole argument re NFB) was talking about reproduction of something (copying if you wish), not quality of the original. As Jan mentioned before, hearing might even be considered irrelevant.
Your post #1101 - I am going to save screen space by not quoting.
I have replied to you before regarding years of experience and "world fame" - let us leave it at that; your memory is short. (And you don't want to push "world fame" as a norm now ... might land you in some really funny company.) Let us just say I have also had me modest moments, but I have never found personal fame used as scientific proof, not even by Einstein. And as for (automatically?) denigrating the hearing of those who do not agree with you ... that was unworthy of you. Seems some of us honestly want to get to the truth, others only to win an argument.
When you use quality of foodstuffs or whatever as an example, we are not on the same page. I (and the whole argument re NFB) was talking about reproduction of something (copying if you wish), not quality of the original. As Jan mentioned before, hearing might even be considered irrelevant.