CFA Topology Audio Amplifiers

[forr]

What's the problem forr?

There have been some great designs presented here that are easily comparable to VFA.

Again, I just do not understand the antagonism towards CFA on this thread.

Because amplification is an application of science, even if subjective results only are considered, and antagonism brought by facts is the essence of science which allows it to live and to grow.
I wouldn't have thought that asking to summarize the progress made in this thread towards the CFA scheme and observed on real circuits could be interpreted as being offensive.

 

[kgrlee]

With 10 transistors front end you can make a VFA that has lower than 1 ppm THD AND IMD in the full audio band , try this with a CFA and post the results when available , i wont even consider PSRR to ease the comparison...

And yet an amplifier with 1 ppm THD + IMD and 10V/us SR is undoubtly better than one with 100ppm THD and 1000V/us SR.

Also on the subject of noise , even if you can have good linearity be carefull that thoses great numbers are not completely ruined by averagely rejected PSU ripples and other potential perturbations...

Wahab, if you'll post a *.ASC of your circuit, I shall attempt what you ask.

The reason I'm asking for the *.ASC is that 1ppm THD20k is not that easy whatever the topology. If you have a VFA design that does this, it will be easier for me to simplify it into a CFA while improving it. If your VFA doesn't quite do 1ppm, I hope you will allow me to just equal that performance. 🙂

It probably won't be simple .. just simpler than your original.

I take it you mean 1ppm THD20k. You may like to enumerate the other performance parameters you'd like to retain. I'm not sure if you are conceding PSRR. 🙂
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forr, I've summarized what we've learnt at least twice now. I'm sorry if the designs that work don't look supa dupa or new to you. But one of the BIG advantages of CFAs is that with simpler designs, CFAs outperform VFAs on ALL the usual performance specs.

Simplicity with performance is BIG on my list of priorities .. far more important than 'new' or 'looks supa dupa'.
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Why are so many people condemning CFAs cos they have zillion V/us slew? Are you saying this makes an amplifier bad? There is no need to condemn an amp for being better than you think is necessary ... except of course on religious grounds 🙂

 

[ontoaba]

. Start to build and LISTEN!

which one you prefer to built? how long you have been "mod" your prototype?

 

[michaelkiwanuka]

...how many quotes do you think I could scrape from different posters in this thread seemingly asserting flat open loop bandwidth, slew rate, speed, CFA front end linearity by themselves are audibly superior? - presented as absolute as fact?


why should I accept such statements as in any way reliable, useful, actionable for audio circuit design? - you couldn't post "CFA" here in any thread at diyAudio for years after I joined without some saying CFA sucks for audio - by some assuring us they design high end equipment, they and their discerning clients hating "the sound" from application CFA in power amps or DAC I/V

True.

 

[gk7]

...why should I accept such statements ...

And if you don't, does anyone need your approval to discuss the CFA topology ?

... fast switching DBT is the only way to establish "sound"...

No, it a test if you can discern A and B under the conditions of fast switching, nothing else.
Certainly not the conditions you have when you listen to music.

 

[Esperado]

it a test if you can discern A and B under the conditions of fast switching, nothing else.
Certainly not the conditions you have when you listen to music.

So true.
While it is easy to figure out any unwanted change plugging a preamp in/out in a chain, i don't see what we can conclude "objectively", when it is about Power amps or Loudspeakers.
We will hear differences, but where is the reference ?

Now, everybody can differ in its judgments/preferences, depending of a lot of parameters: room acoustic, enclosures, type of music, knowledge of real instrument's sounds, knowledge of the recorded source contents, knowledge of the audio evils (distortions, bandwitchs, transients response etc) making us more or less able to distinguish them.
Not to talk of what is revealed only in the long run with various sources, like listening fatigue, slight imbalances of the response curve etc...
Every audio designer, each sound engineer use in its work process instant tests to figure out ...what he prefer ;-)

Everybody is free to prefer something else than his neighbor, but a minimal intelligence is to respect its neighbor's preferences and let-it free to express them.

I don't understand why a handle of naysayers, always the same since the beginning, free to express their own preferences anywhere else, are trying endlessly with a lot of noise to prevent us from moving on this CFA subject.
With high value contributions like:

...So-called "CFAs" are rubbish for audio.

They don't like CFAs ? Perfect: They can open their VFA thread and leave-us in peace, I believe no one of the people interested in this thread will come in their VFA one to annoy them as they do here.

Are CFA fans more educated, open minded and intelligent ?

 

[Lazy Cat]

Are CFA fans more educated, open minded and intelligent ?

None of these, CFA fans simply just have much better hearing instrument (ears-brains).

 

[Bigun]

People are raining on your parade because you insist on telling them you are better. I learned a lot about some of the folk around here from this thread. Best to have a sense of humour 😀

 

[Esperado]

People are raining on your parade because you insist on telling them you are better.

Where do-you read this, Bigun ?
I believe, on the contrary Andrej is a very open minded and modest person working hard, with no certitude, never satisfied. This said, i believe he can be proud of his VSSA.
What he said about his amp's signature is exactly what reported most of the builders. And what reported the reviewers in the first "hifi show" he was exposed.
And what we expect from a CFA: details, 'live', dynamic.

 

[Lazy Cat]

People are raining on your parade because you insist on telling them you are better. I learned a lot about some of the folk around here from this thread. Best to have a sense of humour 😀

To my surprise, the peeceebee has a bigger soundstage than my Honey Badger. It really is an amazing design.

No signal details lost - you hear more.

LC is correct, there is a special quality to the sound, I think the closest word is "transparency". A friend's wife said she could understand vocals on some difficult older music for the first time, just spending a few minutes listening.

Facts, baby, facts hehe

 

[Bigun]

Actually I'm not wanting to point any fingers, I just notice that there are plenty of comments about how one topology is better than another. Whenever this happens people get upset because they feel you are critical of their choices and therefore, of them. It's just a human thing. So why be surprised about how some people react. No issues with the VSSA, I built my own version TGM5. It's all good fun, hopefully.


Hey, LC, you quoted yourself there 😀

 

[tinitus]

well, I have been very pleased with Sonny's Mirand amp design ... but hope to give it some sisters soon 🙄

 

[Lazy Cat]

Hey, LC, you quoted yourself there 😀

Yes, because it is a timeline how conversation went in the other thread, so the PMI's answer is a logical consequence.

BTW I made a lot of low % THD VFA's but, sorry, never got so much info and pleasure from the music than from CFA. I don't know what is the reason, I don't even care, but that is the plain fact. So what is the logical conclusion, to go on with CFA. What else could I do? 🙄

 

[Bigun]

Did you make VFA similar in topology to the VSSA or were they different topologies altogether ?

And where will you go next with CFA, there is already many SSA's ?

 

[Lazy Cat]

Did you make VFA similar in topology to the VSSA or were they different topologies altogether ?

VFA-s were always LTP-s, cascoded/non cascoded, enhanced TIS, cascoded/non cascoded, BJT, triple, BIGBT, MOSFET OPS. What can I tell you, not enough resolution, poor transient-dynamics sound.

Not to mention how many well known producers amplifiers I had at my home for testing or in a shop-studios systems comparisons.

 

[Bigun]

Well I have built both CFA and VFA and been happy with all, but then I can never complain about my own creations, they were all made with love and care. My TGM1 was a clone of the AKSA and it sounds fine and has had many loyal fans yet is an LTP. And TGM5 also sounded very good based on VSSA. But I never did have the chance to hear many different amplifiers - I don't get out much. Perhaps the only way I can get a better idea with my own ears is to build a TGM7 with both VFA and CFA front-end where everything else really is the same, and both versions also simulates the same too (distortion profile, OLG gain/phase etc.). hmmmmm..........

 

[Krisfr]

Anyone have any first hand, as in listening, experience with the bass end of the spectrum with CFA? I got an impression, rightfully or wrongfully, that it, the low end, had some issues.

 

[Esperado]

I just notice that there are plenty of comments about how one topology is better than another.

I hope that if some feel some interest in this thread, it is because they have EXPERIENCED advantages in CFAs. What else ?
My story is even more surprising: I discovered, long time after, that all my preferred amps for myself or the ones i had chose for my studios (listening copies on loan, like the Studer) were near all CFAs.
I realized-it with the Mark Alexander paper, the controversial name "current feedback" was not even familiar to me before, while the first amp design i was part of in a R&D office was of this topology. Nothing exotic at this time, it was a very common topology issued from tubes amps.
About the Mark Alexander, i builded one with demo boards from AD at this time and was very happy by the way it sounded, specially the voices.
Now, if you ask me to define CFAs signature, i will insist on "details", natural trebles without fatigue, dynamic and micro dynamic. Easy listening with easy separation at all levels witch is essential in studio's work.
As i had made experiment with the same amps in both topologies to figure out the differences, it will be very hard to opponents to make-me change my opinion. Witch is mine and i will not impose to anybody.

 

[rsavas]

About the Mark Alexander, i builded one with demo boards from AD at this time and was very happy by the way it sounded, specially the voices.

I was also impressed with the simplicity, performance and listening test report by Mark.
Did you use the Toshiba IGBT devices? and the SSM2131 opamp?
I wonder if it would perform better with a newer opamp?

 

[Esperado]

I was also impressed with the simplicity, performance and listening test report by Mark.
Did you use the Toshiba IGBT devices? and the SSM2131 opamp?
I wonder if it would perform better with a newer opamp?

Yes, i build-it exactly "as-it".
This said, i don't see any advantages, nowadays, to use OPAs as input stage. One of the things i have took for sure, participating to this thread and exploring more. ;-)