Is the CFB topology superior, and why?

[Jay]

Originally Posted by 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.

I myself failed to see what is in LM3886 that is similar to CFB amps soundwise.

[AndrewT]

Originally Posted by Jay

I myself failed to see what is in LM3886 that is similar to CFB amps soundwise.

[Esperado]

Originally Posted by 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.

Can-you develop a little, Jay ?

[ivanlukic]

Jay,

I disagree that HEXFETS in class AB will never sound good enough. For my TV setup I use Pioneer A107amp with Tannoy Mercury M1 loudspeakers. Pioneer uses IRF 530/9530 in output in class AB and the sound is superbly fast, fluid and musical.

[homemodder]

Originally Posted by 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.

You must have been speaking to a salesman that either doesnt have a clue what he is talking about or simply promising you whatever to make a sale.

Here the folowing statement from Cyrus :

"The input signals are relay switched immediately as they enter the Cyrus Straight Line, ensuring maximum signal fidelity and effectively no X-talk between inputs. The propriety current-feedback amplifier design constitutes the basis of the Cyrus Straight Line. Our application of current feedback principles, rather than conventional voltage feedback methods, enables ultra-fast slewing of 700V/mS and negligibly low distortion at higher frequencies. The result is an exceptional sweetness and clarity in the mid-band with an attractive silky top end. Finally, an authoritative bass response with convincing scale and weight underpins the overall rendition of program material."

Like I said before Cyrus has only produced CFB amps since model 3.

[catalin]

Why not satisfy both cfb and vfb listeners ?
a wonderfull sziklai
My ears are delighted with 60db of CFB and 20 db of vfb
Also it is possible to equalise the cfb and vfb factor by making equal the ratios:
R15/R2 = R5/R8 .
If we want to have the cfb dominant we can decrease R15 to 10kohm for example and put in series a capacitor of 22uF to minimise the voltage drift in dc .

[ivanlukic]

Homemodder,

Like I said Cyrus Straight Line is CF, no doubt about that, but it seems that it was one time experiment, and I can not be sure that their products after that are CF unless I see schematics (which I do not have). How do you know that the latest incarnations of series 6 and 8 are CF? Do you have schematics? There is nowhere such claim from Cyrus. The only model for which CF is explicitly claimed is Straight Line.

[Esperado]

Originally Posted by catalin

Why not satisfy both cfb and vfb listeners ?
a wonderfull sziklai.

Nice idea to increase common mode rejection to CF amps.
Have a look to SSA on how to apply on symmetrical topologies.
Did-you tried all combinations of the two, to find the best FB percent of each ?
[edit] Looking at your curves shows well the speed differences between the two FB :-)

[dadod]

Originally Posted by catalin

Why not satisfy both cfb and vfb listeners ?
a wonderfull sziklai
My ears are delighted with 60db of CFB and 20 db of vfb
Also it is possible to equalise the cfb and vfb factor by making equal the ratios:
R15/R2 = R5/R8 .
If we want to have the cfb dominant we can decrease R15 to 10kohm for example and put in series a capacitor of 22uF to minimise the voltage drift in dc .

Haw did you came to those values for CFB and VFB, and at what frequences?
In your schematic R15 is 330k and you states 60db of the CFB(dominant) and later you said to make CFB dominant decrease R15 to 10k. It looks like your claims are unsupported.
I like your idea, but you have to support your claims.
dado

[ivanlukic]

There is also one practical advantage of CF topology. It is more tolerant of low grade interconnects and speaker cables, it works with anything at hand. With VF it is endless search for the right combination of interconnects and speaker cables that will restore "the air". With CF, topology itself is doing the job.