Is the CFB topology superior, and why? - Page 27 - diyAudio
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Old 2nd November 2012, 08:39 PM   #261
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Quote:
Originally Posted by Elvee View Post
One thing has to be remembered at all times: without at least a semblance of metric, no progress is possible (except in religion, of course but it is exempted). Audio is no exception to that rule.
On that, i agree 100%. And it is a religion. (joke again)
I had made the effort to provide two sims of the same amp, VFB vs CFB. You can't deny my effort on that. Sims are not a kind of metric ?

For the other part of your answer, there is a funny thread, in this forum about sound of cables. I can listen differences of sound with different loudspeakers cable's capacitance on long distances, (special when they make the amp oscillate), with non linear Z loudspeakers and diameters, no more. And my answer about cables is this citation: "I tend to prefer those witch conduct electricity". Read my signature, to know my position.
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Last edited by Esperado; 2nd November 2012 at 08:52 PM.
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Old 2nd November 2012, 09:25 PM   #262
catalin is offline catalin  Romania
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Quote:
Originally Posted by Elvee View Post
That's what I said, a mistake: measuring the OLG of a circuit block with a third terminal injecting something into the said block is wrong
.
Please pay attention Elvee :There is no OLG shown there ,is only gain for the first stage .
The measurement shows the gain and phase of the Ltp ..
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Old 3rd November 2012, 04:59 AM   #263
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Quote:
Originally Posted by Elvee View Post
then some guy arrives, picks and chooses a bit or another of various theories to their own convenience and claims he has discovered something
By the way, and despite i had never pretended to have invented anything else than the patents i have deposed, look at this schematic of the Mach50 we designed in 1970 and a link to the site of a guy witch had make a restoration of it. (Please, look at the feedback !)
SCIENTELEC Haute Fidélité française
and the measurements he made (remember 1970 !)
RightMark Audio Analyzer test : Mach_A50S

The" audiophile" word was not even invented. And, sorry, but, yes we used to listen to our work (not the way you describe, but with criticism) as much as we where making measurements at each step, because there is no other way to work for audio in a research and development office.
We where the first, i believe to provide a 24pos rotator with constant impedance to replace potentiometers and a physiological circuit, following exactly the Fletcher and Mudson curves.
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Last edited by Esperado; 3rd November 2012 at 05:17 AM.
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Old 3rd November 2012, 07:49 AM   #264
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by Elvee View Post
with proper metrics to decide which one is better, and proper methodology to remove statistical noise from the results..
If there is ever such metrics.

With blind test, I will set up a system that will display the strengths of the CFB. And blind test, especially by experts, tho not scientific, is the best way to decide which one is best. Because there is no scientific approach, even if you want to pretend that there is one.

I trust my honesty. If I found the VFB sound better I will right away throw away my CFB. I have no special relationship with CFB anyway. And if everyone is as honest, no need a blind test. Just show two amps and we will build both of them and give our reports.
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Old 3rd November 2012, 08:00 AM   #265
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by ivanlukic View Post
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.
"Good enough" is relative. Your Pioneer (and speaker) is for "kids". It is not even at average level. It uses an opamp that if I'm not mistaken around 6v/us slew rate. Very bad. Go to SSA thread if you want a simpler, yet better amp.

ADD: The Stochino is the best amp I have built with hexfet at class-B.

Quote:
Originally Posted by Esperado View Post
Can-you develop a little, Jay ?
It's just like the basic of latfet-SSA as built by Nico and Shaan, but the latfet is replaced with HEXFET plus a (5401/5551) driver. I was trying to help others with "cheap" SSA/CFB (using cheap hexfet, and no need big heatsink and transformer), but the result was not good. Hexfets are for class-A I guess.

Last edited by Jay; 3rd November 2012 at 08:03 AM.
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Old 3rd November 2012, 11:06 AM   #266
Elvee is online now Elvee  Belgium
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Quote:
Originally Posted by Esperado View Post
look at this schematic of the Mach50 we designed in 1970 and a link to the site of a guy witch had make a restoration of it. (Please, look at the feedback !)
SCIENTELEC Haute Fidélité française
The vast majority of the amplifiers from that era (~'65 to '75) had a single supply and capacitive coupling.
That configuration of the single transistor used as a subtractor was therefore the most straightforward, economical and effective, and it was used in ~75% of amplifiers designed at that time.
First, three examples using Ge transistors, from Philips, Siemens and Thomson.
Then, some later examples based on silicon.

But there was no awareness or intent from the designers to create CFB, quite the opposite in fact: this effect was seen as nuisance, as it spent uselessly part of the loop gain.
There were therefore "clever" attempts to circumvent the effect, without using a disproportionately large feedback electrolytic (necessitated by the low impedance of the FB network).
The next pic shows an example of such a smart scheme, where the speaker is part of the impedance of the FB divider.
Finally, a curiosity: an amplifier duplicating the tube OTL, with a composite MOS/bjt IC as input, also with CFB.

Now, you could say that CFB already existed at the time, but unbeknown of the designers, "à l'insu de leur plein gré", just like Mr Jourdain had been speaking prose all his life without knowing it.
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Old 3rd November 2012, 11:11 AM   #267
Elvee is online now Elvee  Belgium
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Two more examples from Philips:
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File Type: jpg 100_5346.JPG (297.2 KB, 62 views)
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Old 3rd November 2012, 11:30 AM   #268
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Jay,

I never claimed that Pioneer/Tannoy pair is state of the art. Like I said it is for low power reproduction from TV/FM tuner, it is not my main music reproduction system. Although budget priced, Pioneer amp is excellent sounding and the circuit is very good. It is not run of the mill Japanese product but the work of some clever and very competent Japanese engineer. I know Stochino circuit and I do not think that building it would bring any real improvement in sound quality over Pioneer circuit.

I do not think that Japanese engineers are less competent than any other engineers just because they remain nameless and because they work for big companies. In fact, just the opposite may be the case.
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Old 3rd November 2012, 12:04 PM   #269
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Quote:
Originally Posted by Elvee View Post
Now, you could say that CFB already existed at the time, but unbeknown of the designers, "à l'insu de leur plein gré", just like Mr Jourdain had been speaking prose all his life without knowing it.
It was a common practice in tube amps, long time before Germanium, yes.
I'm impressed with your schematic library ! We had no time, on our side, to look at other's company work. some in the datasheets, yes...
Note: Our amp had something a little special at this time, using the first planar power transistors for more speed (BDY56, if i remember well)...
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Old 3rd November 2012, 12:28 PM   #270
wahab is offline wahab  Algeria
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Quote:
Originally Posted by Elvee View Post

Now, you could say that CFB already existed at the time, but unbeknown of the designers, "à l'insu de leur plein gré", just like Mr Jourdain had been speaking prose all his life without knowing it.
Quite some memories...

I have the french book wich you are displaying schematics from.

Just remember the whole bunch of theses early unwillingly CFB designed amps ,
and the remaining impression after all this time is that , although
a majority did more or less work , they were also as a majority
of poor quality..

The generalisation of the LIN was a relief and we could then talk
of hifi amplifiers and get rid of thoses designs where you could
often improve a parameter only by degrading another one....
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