Not unexpectedly "VFA" proponents arguments is "build (a VFA) and listen"...
Why not "build and measure" ?
It s not by chance that people promoting half baked amplifiers
unrelentlessly talk of "good sound" , yet , they ll never produce
numbers , all we can seen are sometimes square functions response ,
as if it was the ultimate parameter in sound quality in the mind
of thoses people who obviously equate speed with linearity ,
of course that is total non sense but it seems to work for whom
has a vested interest in advertising average amps as being
the most linear , wich is totaly untrue and is known , hence
the measurements being discarded.
Why not "build and measure" ?
It s not by chance that people promoting half baked amplifiers
unrelentlessly talk of "good sound" , yet , they ll never produce
numbers , all we can seen are sometimes square functions response ,
as if it was the ultimate parameter in sound quality in the mind
of thoses people who obviously equate speed with linearity ,
of course that is total non sense but it seems to work for whom
has a vested interest in advertising average amps as being
the most linear , wich is totaly untrue and is known , hence
the measurements being discarded.
Man, you are still a student, it will still take a while before you have finished digesting your books.
Because you still don't understand what i'm talking about, i will explain-it in a manner a student can, may-be, understand easier:
An externally hosted image should be here but it was not working when we last tested it.
I pretend (nobody is obliged to agree) that the green part is perfect for audio transparency, and the red not.
CFA topology can make, with the same devices, the transition point between green and red up to 10X higher in frequency.
This to *try* to explain the positive difference in listening experience reported by near everibody listening to a CFA amplifier. Including all the VSSA new builders.
This correlated by many people witch prefer *no feedback* design, at the high price of sorted and matched expensive components.
I have spend a lot of time in my life to design, build, compare, and listen closed loop amplifiers and pre-amplifiers. That is just the conclusion due to my personal experiences. And it took long decades for me to reach this conclusion.
Did -you make 1/10 of the experiments i have done in > 40years dedicated to audio design, music recordings and reproduction ? I have like a doubt. This, at least require a minimal respect.
As said Bob Cordel, you seem just able to criticize. And make personal attacks instead of valuable technical argues.
Why don't you try to understand instead, and, when something looks strange to you, because it is not what is told in your school books, to figure out by yourself ?
Have-you ever build a good CFA ?
If Google is still here in 20 years, you will be shamed of you. Both on a technical point of view and your lack of education.
Group delay ? i'm very impressed by your knowledge. Where where-you in 1970, when we produced monitors for ORTF (with my friend Raymond Cooke from KEF) with a near flat group delay curve, aligning speakers, tweaking filters ? (Sorry for the name dropping, but i'm upset)
Now, EOT for me, it seems impossible to exchange friendly and intelligently about audio design in this forum.
These arguments remand me of those of various engines . These are harmonic and strength . The engines with then greatest strength performance ratio is probably V6 . Straight 5 is interesting as no one piston is at TDC at any one time ( small balancing required ) . However the V8 sounds great and I suspect that always wins .
In British libraries 621 is electronics . It is also Marine Diesels . I learnt plenty for being distracted into reading about them . Not least harmonic distortion called vibration . Caused by the fantastically high compression ratio . A square top to a sine wave . In mechanical engineering such discussion as here die very quickly as do the designs . Formula one was spared this by taking the RPM back 1000 and making the engines reliable . In F1 " walk the walk" as well as " talk the talk " is the proof . Every team has great diagnostic tools , only one seems to know how to use them . Measurement is fine , winning is very different .
In British libraries 621 is electronics . It is also Marine Diesels . I learnt plenty for being distracted into reading about them . Not least harmonic distortion called vibration . Caused by the fantastically high compression ratio . A square top to a sine wave . In mechanical engineering such discussion as here die very quickly as do the designs . Formula one was spared this by taking the RPM back 1000 and making the engines reliable . In F1 " walk the walk" as well as " talk the talk " is the proof . Every team has great diagnostic tools , only one seems to know how to use them . Measurement is fine , winning is very different .
Simple 60 Watt Power Amplifier
Looks like the origin of the CFA . The old HC Lin idea ? Nice to see Mr Elliot keeping it simple . Feels like it's worthwhile when simple ( see later version ) . Allows the music to flood through .
Looks like the origin of the CFA . The old HC Lin idea ? Nice to see Mr Elliot keeping it simple . Feels like it's worthwhile when simple ( see later version ) . Allows the music to flood through .
I red Bruno Putzey's F word article and noted he admited in the text that low feedback designs sound worse than no feedback designs. I keep Denon PMA 737 integrated amp in my collection as an example of zero (global) feedback design. (Yes, there was such mass produced amps 25+years ago). This amp sounds very good but is erratic, inconsistent performer. With some music it sounds excellent. Inherent distortions work like sound processor enhancing experience with some music. But with some music it sounds bad. I noticed that feedback designs sound much more consistent and there is no doubt in my mind that feedback is the tool that should be used in audio amps. Only question is which type of feedback and how much of it? In my humble opinion in audio amps CFB works better. I am not pretending that I am connoisseur of control theory nor I am sure that the theory will suffice as explanation.
Bruno (and other designers) have shown that what is important for audible quality is how much loop gain you have at 20kHz which you can use for feedback; say the right top of your red block.
Then, if you increase the loop gain toward DC (your green block) it doesn't make a difference.
What many people do not realise is that when you design amps with a flat wide bandwidth (like low or no feedback amps), which would be the red and green the same, almost always you end up with the top of the red block lower than with the first case.
So although visually it looks much flatter, because it is lower at 20kHz, it actually sounds (much) worse.
jan
If you spent "a lot of time in my life" in uncontrolled listening tests, then I fear you've wasted a great deal of your time.
If your listening tests had been controlled you would have come to the conclusion that there is no audible difference between a well designed VFA and a well designed so-called "CFA", although "CFAs" are demonstrably inferior to VFAs in audio applications at least.
100% correct.
I would disagree only with the "20KHz" above; if the design target is a minimum of distortions of a 20KHz fundamental, then what really matters is the amount of loop gain at 40KHz and (in particular for a Class AB amp with crossover distortions) at 60KHz. Those amounts of loop gain help lowering the 2nd and 3rd harmonics of the 20KHz fundamental.
Eperado,
My comment that you quoted was aimed directly at class-D and not the cfa vs vfa argument. I was only saying that I don't think that there was anyone building a class-D amplifier from scratch as a diy project but speaking about commercial designs that are created by Bruno. I am not sure that there is at this time a demand to build diy class-D amplifiers. Not yet anyway.
Nigel,
Where do you get that drivel about a V6 engine being the best design? That engine configuration is one of the worst for balance reasons and is only made because it can be packaged smaller than a straight 6, it has no inherent advantage over a V8, actually any V8 is much easier to balance than any V6 engine. Sorry I have seen the problems involved in trying to make a V6 work at high rpm and high horsepower and it isn't for the faint of heart. Watched the entire development of the racing turbo Buick V6 program and that was a major undertaking to make that engine stay in one piece. The engine in the Rover is a direct decedent of an earlier Buick aluminum engine made in the 60's here by GM and sold to Rover. And the 5 cylinder engine is another story all together, fine if you want a slow low rpm diesel but not much else.
My comment that you quoted was aimed directly at class-D and not the cfa vs vfa argument. I was only saying that I don't think that there was anyone building a class-D amplifier from scratch as a diy project but speaking about commercial designs that are created by Bruno. I am not sure that there is at this time a demand to build diy class-D amplifiers. Not yet anyway.
Nigel,
Where do you get that drivel about a V6 engine being the best design? That engine configuration is one of the worst for balance reasons and is only made because it can be packaged smaller than a straight 6, it has no inherent advantage over a V8, actually any V8 is much easier to balance than any V6 engine. Sorry I have seen the problems involved in trying to make a V6 work at high rpm and high horsepower and it isn't for the faint of heart. Watched the entire development of the racing turbo Buick V6 program and that was a major undertaking to make that engine stay in one piece. The engine in the Rover is a direct decedent of an earlier Buick aluminum engine made in the 60's here by GM and sold to Rover. And the 5 cylinder engine is another story all together, fine if you want a slow low rpm diesel but not much else.
Cars "analogies" should be definitively abandonned since
they re creating more confusions than helping understand
a given concept.
I often read that amps or PCs amateurs use such analogies
but i never heard a car addicts using amps or PCs to better
explain their thoughts about their cars....
they re creating more confusions than helping understand
a given concept.
I often read that amps or PCs amateurs use such analogies
but i never heard a car addicts using amps or PCs to better
explain their thoughts about their cars....
Unless of course you want to equate a turbocharger to a feedback loop. Actualy cars dynamic parts can follow the same rules
that electric systems with the same explicit differential
equations but such points are never used in comparisons
since knowledge of such laws would render useless such
analogies.
Brakes regulations :
Memoire Online - Analyse du comportement de la servovalve electro-hydraulique lors de freinage des roues d'un avion (cas de Boeing 737-NG) - Charly MENGAWAKU JEAN
that electric systems with the same explicit differential
equations but such points are never used in comparisons
since knowledge of such laws would render useless such
analogies.
Brakes regulations :
Memoire Online - Analyse du comportement de la servovalve electro-hydraulique lors de freinage des roues d'un avion (cas de Boeing 737-NG) - Charly MENGAWAKU JEAN
OT/
VR6 - a compromised straight six when it comes to thermodynamics and mechanical balance. Developed to bring 'status' to small eighties cars with transversely mounted engines.
\OT
/OT2
It depends how the exhaust pulses are mixed together. If done optimally even a classic Chevy V8 can sound 'wimpy': Sound of 180 degree headers on a Chevy V8 - YouTube
\OT2
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