Several power amplifiers from NAD such as 208, 214, 216, 218 etc have symmetric CFA topology. Stereophile review NAD 218 (incl. measurements).
L.C. You are a cheater !!! You forgot to count the current sourcesClear example of superiority of a simple CFA (6 transistors - VSSA) over complex VFA (18 transistors - SYMEF).
Joke apart, i still don't understand why this old CFA way to apply feedback to an audio amplifier continue to generate such controversial and aggressive reactions from VFA addicts. While, step, by step, so many designers witch have tried-it in real world never will return back to VFA. I imagine it is your case, don't it ?
Audiophile side, a lot of CFA had been noted as very musical along years, and often preferred at their times, while nobody noticed they were CFA.
It happened to me in my studio. I had a very expensive VFA amplifier, considered as top of the art at the time. One day, my friend from Studer France brought-me a Studer Amplifier in order to get my opinion. We listened to it and guess what ? I refused to unplug-it and exchanged-it with a check. Despite it was lot less powerful than my luxurious previous one. I realized many years after it was, once more ... CFA !!!!
Clear example of superiority of a simple CFA (6 transistors - VSSA) over complex VFA (18 transistors - SYMEF).
Jason's subjective impressions are so consistent with what I like in symmetrical CFB amps sound! I have never seen him, nor Esperado, nor anybody else who built any version of VSSA, or any other symmetrical CFB amp. It is impossible that we are all wrong in our subjective impressions. But the other side only has purely technical objections, which we see are probably unfounded, no comment on sound whatsoever! Nobody explained how "better VFB topology" turns it's "superior" technical qualities into better sound. The only available subjective comments testify that CFB sounds better.
You got it wrong...
VFA proponents would never rely on subjectives assumptions
and claim that their designs "sound good" because they know
that such claims are not scientific.
Of course their amps are accurates , more than the so called
VFAs , but to assert such claims they ll provide measurements
contrary to "VFA" supporters who rely only on non verifiables
psychologic claims since they know that technicaly their designs
are more often than not of inferior performances.
I don't think this is in general true, it must be something specific to your implementation.
Other that the triple devices, the only other thing that (slightly) affects the triple stability is the source impedance. But this is usually the output impedance of the VAS/TIS, tamed at HF by the compensation network.
VFB addicts disguise their lack of interest in sound quality, the only thing that really matters, in technical jargon.
Obviously, VFB addicts are not interested in audio at all.
CFA vs VFA
Never? I returned back to VFA.
The first design is from 2008, the second one is from 2012. The latter performs spice-wise far better in every aspect (admittedly, not built yet).
Cheers, E.
Never? I returned back to VFA.
The first design is from 2008, the second one is from 2012. The latter performs spice-wise far better in every aspect (admittedly, not built yet).
Cheers, E.
Attachments
L.C. You are a cheater !!! You forgot to count the current sources
No, not really, jkuetemann compared VSSA in PeeCeeBee version that means only six transistors compared to SYMEF's 18 BJT-s. That means basic of them all can beat VFA. Just imagine what CFA in more accurate version can do.
Yes, yes all true in sim, but as always: build, listen, compare, know. In that order.
Exactly Ivan, we all are not deaf and have lots of experiences with many amps, commercial and DIY.
jcx wrote ". . . . and if CFA is single pole compensated while VFA practice today does understand 2-pole schemes fairly well then 2a 2-pole compensated VFA can easily beat CFA in loop gain to beyond 20 kHz do you even know how how to add 2-pole compensation to CFA?"
Yes, I have tried that and got 2ppm at 20k. Importantly, this is happening with circa 55dB loop gain at that frequency but would have to see the results in a practical amplifier.
What is interesting is this level of performance is with only 55 dB of loop gain at 20 kHz. I'd be tempted to suggest his reflects the inherent linearity of the topology (output power c. 280 W into 8 Ohms).
Anyone chasing sub ppm distortion blindly, and using this as a measure of amplifier performance is IMV sadly deluded.
Yes, I have tried that and got 2ppm at 20k. Importantly, this is happening with circa 55dB loop gain at that frequency but would have to see the results in a practical amplifier.
What is interesting is this level of performance is with only 55 dB of loop gain at 20 kHz. I'd be tempted to suggest his reflects the inherent linearity of the topology (output power c. 280 W into 8 Ohms).
Anyone chasing sub ppm distortion blindly, and using this as a measure of amplifier performance is IMV sadly deluded.
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VFB addicts disguise their lack of interest in sound quality, the only thing that really matters, in technical jargon.
Design by ear is hardly synonym of research of quality ,
let s say that i dont believe that what measure way better
can sound worse.
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I am perplexed! How come that people educated in engineering, people that are by definition intelligent, can be so narrow-minded? I am not saying that amps should not measure well, I am only saying that if the sound is not perceived as better all the effort is wasted.
I'd like first to thank you about excellent and I opening articles and finally the book too.
What I am looking for is, how to make amplifier (box) internal connections in case of multiple channels (usually at least two). Every picture is drawn so that there is only one channel. In case of two channel the amp module signal gound is connected to start point and RCA-input connector to amp module inlcuding singnal gound. Signal grounds from two amp modules are joint at star point but also at the RCA-connector set (module) or at least in the pre-amplifier box. This means that it is possible to have signal modulated current going via signal ground wires via RCA-connector module (or via pre-amp).
Somehow I thik that the power ground of amp module power stage capacitors (in amp-module) should be grounded separately to star ground and not together with signal grounding (low power stages).
When one of the channel is loaded it draw current and causes voltage over power lines to amp-module but because of the this voltage drop it also causes current and voltage drop over groud wire from amp-module to star ground. After this there is "modulated" current in signal ground wire from both amp modules to RCA-module.
It does not matter if distorition is 0.0000.... if if the input signal gets dirty.
In some desings I have seen some sort of differential (or balanced how to call it) input in the amp-module to avoid signal ground loop.
I propose this as one possible topic.
I am perplexed how you can be sure you will distinguish good designed CFA from good designed VFA in double blind test. Or you just don't believe in double blind test because you are sure CFA is better?
hi, Edmond, so, we are waiting to your listening impressions. Because this is all about. I don't pretend neither i will never use anymore a VFA part somewhere in a future design, but...you know... you design or build a new amp... and it sound not so good as your previous one...
Look what happened when i tried to provide two files (one VFA, one CFA) of the same amp that sim experts can play with in order to explore and compare technical aspects of the both technologies...
I indicated what i believe a nice and simple way to see where to look-at in the closed loop.
Who explored this here ?
No, some prefer to pretend my files (just sim tools) are not working and fire me.
To Wahad, or JCX, my CFA currents and polarizations were tuned in my LTspice to minimize distortion (so called class C gives 0.001% with a 1000Hz signal at +-55V) in a total blind experimental way. I made no calculations.
I just run them today, as-it, to make those images.
I don't believe in sims, but i believe in the *relative* numbers they provide.
I don't want to loose time to justify more because it is boring and time consuming to play with sims and provide hundreds of images just to pretend in forum my pseudo 'have a bigger' than your: it does not play any note of music.
So, please, if my files or my models, or anything does not work in your home, i'm far to be an expert in simulation, as i just begin with ... play with the current source and input device collector values the way you want for they work with your models and your simulator in order to *explore* for you and the other members (in an objective manner, not to demonstrate your religion) the ways the two topologies behaves. It will be more productive than to fire me, and that was all my purpose.
Bonsai, may-be you can help us on this ? (and answer to my question about your advanced error correction work ?
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Hi IvaneLukicu !
I was 100% confused several years ago when me and my few friends have been made comparative listening test after my repairing of two old Japanese apparatus ,
First one was mighty Kenwood KA-9x , VFB based , 2x 120W and second one was old Sansui 221 receiver , with 2x12W generated from STK013 CFB based chip Amp.
Kenwood specs say 0,008%THD at rated power , and Sansui specs say less than 1% at rated power .
The clear test winner was small Sansui !!! , with well defined bass spectrum which goes very deep , at least one octave lower than Kenwood ,also with very natural tonal balance and no listening fatigue at all , contrary to Kenwood with his narrow & brute bass power and very precise defined highs which was irritating ours ears all the time .
Even today in my kitchen I use 24/7 that small old Sansui 221 but only for his FM section which feed signal to by me heavy modified Revox-A78 ,CFB singleton Amp.
Regards !
I was 100% confused several years ago when me and my few friends have been made comparative listening test after my repairing of two old Japanese apparatus ,
First one was mighty Kenwood KA-9x , VFB based , 2x 120W and second one was old Sansui 221 receiver , with 2x12W generated from STK013 CFB based chip Amp.
Kenwood specs say 0,008%THD at rated power , and Sansui specs say less than 1% at rated power .
The clear test winner was small Sansui !!! , with well defined bass spectrum which goes very deep , at least one octave lower than Kenwood ,also with very natural tonal balance and no listening fatigue at all , contrary to Kenwood with his narrow & brute bass power and very precise defined highs which was irritating ours ears all the time .
Even today in my kitchen I use 24/7 that small old Sansui 221 but only for his FM section which feed signal to by me heavy modified Revox-A78 ,CFB singleton Amp.
Regards !
This amp, also made by sister company Revox, is one of the first having a diamond input and so-called CFA :
Analyse du Revox A740
The teams of La Nouvelle Revue du Son and L'Audiophile (where this amp has been described ) which merely consist of very subective reviewers were not very keen on this amplifier.
It has not been a very successful product.
Some years later, Revox presented a power amp with a differential input.
The same reviewers then told it was the best amp that Revox ever made.
The conclusion is that nobody can't pretend to personify a universal feeling.