Is the CFB topology superior, and why?

[ivanlukic]

Esperando,

I completely agree with you that CF amps sound generally considerably better than VF amps, much more involving and engaging, yet not fatiguing at all. Unfortunately I do not have one, but intend to buy it. One recent example that I heard is Cyrus Straight Line which is their only CF amp. It sounds much better than any of their VF amps.

But I am in doubt if it is gain peaking, that Mark Alexander describes as peculiarity of most CF amps in Apendix of his CF App. Note for AD, that I like?

[Esperado]

"not the labels you put on a configuration"
Did i mention "Nested Differentiating Feedback Loops" ?

[homemodder]

Originally Posted by ivanlukic

Esperando,

I completely agree with you that CF amps sound generally considerably better than VF amps, much more involving and engaging, yet not fatiguing at all. Unfortunately I do not have one, but intend to buy it. One recent example that I heard is Cyrus Straight Line which is their only CF amp. It sounds much better than any of their VF amps.

But I am in doubt if it is gain peaking, that Mark Alexander describes as peculiarity of most CF amps in Apendix of his CF App. Note for AD, that I like?

Since model 3 which is 20 years old, Cyrus has only made CF amps so probably you were already comparing differences between CF amps and not VFB vis CFB.

[AndrewT]

Originally Posted by ivanlukic

...............Cyrus Straight Line which is their only CF amp................

Originally Posted by homemodder

Since model 3 which is 20 years old, Cyrus has only made CF amps ...........

which is correct?
I have read Cyrus' literature and cannot recall many/some references to current feedback.

[Esperado]

Originally Posted by ivanlukic

But I am in doubt if it is gain peaking, that Mark Alexander describes as peculiarity of most CF amps in Apendix of his CF App. Note for AD, that I like?

Hi, ivanlukic
Have a look to this thread: http://www.diyaudio.com/forums/solid...-new-post.html
About Mark Alexander amp, it is a special kind of approach. He used an integrated circuit as an input device, current feedback, with some kind of error compensation: As the efficiency of the OPA decreases with frequency, the current mirror sensing its consumption increase the level, increasing bandwidth.
I had build one, at this time, and it was sounding very good, indeed. "Involving and engaging, yet not fatiguing at all" as you describe. This can apply to my actual amp, as well.

An other approach to that kind of easy and fast reproduction feeling can be a good class D, like the Hypex NC400. Andrej Lakner, the author of SSA said, comparing it with his curent-feedback baby: "...can say firmly the amps are similar in character and musical presentation in general. From there on, subtle differences are noticeable, some in a favor to NC400, some to SSA, have to be fair and honest."
You can rely on him, about "subtle": He has golden ears. And use them at each steps of his designs.

When two amps with so different approaches are "similar", we can believe on their transparency. That kind of transparency i had never heard with VFB, smooth or harsh. That kind of transparency Elvee seems to don't believe in.

[ivanlukic]

AndrewT,

After hearing how good Cyrus Straight Line sounded I contacted Cyrus to find out if newer products are CF and they said that they are VF! I only have schematics of Cyrus 3i and it seems to be CF though producer does not explicitly mentions it.

Please note that I am not engineer, I do not have neither knowledge nor means (lab) to prove anything but my subjective preference is for CF. And that is very consistent impression from product to product, through the years.

[ivanlukic]

Readers of this thread may find it helpful to know that recent Arcam A28, and probably A38, use Alexander CF circuit although this is not explicitly mentioned anywhere! The only important difference is that Arcam use bipolar Sanken Darlington output instead of Toshiba IGBT in Alexander's original circuit.

[Jay]

The worst CFB amp I have built was SSA-HEXFET in class B. Not a surprise to me because I will and have assumed that IRF in class-B will never sound good enough.

[ivanlukic]

I believe that superb sound of CF is due to high gain at HF, that the sound of CF is frequency response related. But VF circuits can achieve similar results albeit only in ICs. In my opinion LM3886, although VF, sound similar to CF, because of high HF open loop gain. Since everything is packed in such small area HF losses are much lower and sound is much more similar to CF.

[Jay]

Good question, is the CFB topology superior, and why?

It seems the thread is not moving to an answer. I don't seek an answer here as I think I know it by ears.

I mean, long time ago when people preferred BJT over MOSFET, I preferred MOSFET. Not because MOSFET sounds better than BJT, but because I can hear in MOSFET what I cannot hear in BJT. So I want a good MOSFET design that give the MOSFET sound character, plus those goodies that can be given by BJT amps.

Same with CFB amps. It is not true that CFB amp is better than VFB amps. But it seems that a CFB amp can give something that VFB amps cant. So what I want is a good CFB amp that is as good as the best VFB amp, plus its own good character.

I think theoretically Christophe's explanation did make sense, and I agree. But I don't care with theory. Just give me your best VFB amp so I can listen and see if it can give what a CFB can.

Very often, people have different opinions (and never agree with each other) simply because they have different hearing skill. Who knows this is the case here? Giving an amp example will clear the doubt.