Not much wrong. CFA, as we know it, is a circuit topology rather than a "feedback type". This topology can be analyzed and it's specific properties revealed by using the standard feedback theory and formalism. There's nothing magic about, and in the most common cases the negative feedback is (out of the four known types) parallel out, serial input, which is, funny enough, voltage in, voltage out).
Very high SR is coincidentally a natural property of the CFA topology, but there's nothing that would stop a VFA (not necessary a long tail pair differential input) to have very high SR as well.
Frequency compensation, is simpler for a CFA if you don't know what you are doing, or you don't care about any optimization, and significantly more complex if you really get into the details and optimization.
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The so called H-bridge input has this property as do any number of slew enhanced typologies each with their own peculiarities. Some form of slew enhancement by itself does not make a CFA. I took CFA-B to be buffered feedback CFA a VFA to be sure.
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Rfeedback is in the forward transfer function so yes it qualifies. You would be hard pressed to get sub-ppm THD with this topology doesn't Dick want that too? Any non-linearity in the input devices is not included in the feedback, not that this matters at some point I personally think for audio the THD numbers can be fairly lax and still sound just fine.
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You guys are all nuts. Nuts.
One comment from Richard followed by a damn 😉 from me and you're all going nuts again.
Ridiculous.
One comment from Richard followed by a damn 😉 from me and you're all going nuts again.
Ridiculous.
Be calm my friend, it is all OK in the end. You probably don't get this but it's like the Woodwright vs. Norm Abrams on PBS USA.
Wrong guess.
I am an antichrist
I am an anarchist
Don't know what I want
But I know how to get it
I wanna destroy passer by
Yeah, but he used the money to rebuild his crews. PiL is in top shape today, saw them at Indigo at The O2 back in June.
When bettie page was on the run
And my west was way out west
And louis brooks speak the crooks
The greatest pornographic country in the world
Welcome to america USA
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Its great fun for me to torture some here. Like Waly the terrorist. 🙂 {I love you Waly]
I think we all by now know something about CFA and VFA. but there seems to be some problem with my preference for CFA and maybe CFA-B topology. Maybe it is similar to JC's preference for the topology he has worked out and continues to use.
As often happens, I ask for what is possible to do but far above what might be minimally required. I asked for highest SR, lowest distortion, high power (=/>200W/8), symmetrical topology, etc. Nothing about high/low fb. For myself, the CFA was easily able to meet all to a very very high level of performance. So does it Sound any better than run-of-the -mill VFA designs? I think so. Enough to put my money where my mouth is. Several people over here in DIYAudio-land have met the challenge with great success.
Now I havent said such performance cannot be done with VFA and maybe they would also sound superior with similar specs? Bonsai and OS has done comparisons this way to learn about any perceived differences. Bonsai has described the CFA quit accurately on his web site.
THx-RNMarsh
This is what the engineering mystery is all about. I suggested first making a very high slew rate (SR) amp of ultra low distortion to see what happens. The CFA's strength area. It just sounded even better than best effort VFA. BUT, the VFA has since been tweeked to get similar results to CFA and I havent heard those. And, the CFA has been tweeked with -B to outwardly behave like VFA... so the gap is closing due to these newest efforts to compete with CFA's strength area.
The internal CFA with buffered (-) input behaves for app enginners like VFA but keeps speed up etc. Does CFA-B have improved PSRR? If so, IT maybe the design of the future for all High-End amps ---- IMHO, of course.
[-B = CFA's minus input Buffered]
I suspect the established SR estimated as adequate for audio amplifiers is too low??
THx-RNMarsh
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Richard, I think that it is the tendency for CFA amps to have higher open loop bandwidth is the most important difference between VFA and CFA designs. It is true that SR will also improve, perhaps, but after 100V/us or so, it is difficult to justify more. Open loop bandwidth, however is hard to get over 10,000 Hz and is usually a lot less with VFA designs. Ron Quan's latest paper, given at the LA AES, last week, partially addresses this issue. Yes, PIM is back! (it never went away) '-)
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