Is the CFB topology superior, and why? - Page 28 - diyAudio
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Old 3rd November 2012, 01:20 PM   #271
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Originally Posted by wahab View Post
they were also as a majority of poor quality...
So true.
First transistors amps had a justified bad reputation. At this time, no one i knew was able to compete with my tube Macintosh.
The company i worked for at this time had started his history, before our arrival, selling kits and amps, based on an RCA schematic, with 2N3055s. Cheap and absolutely awful !

We had worked a lot on this Mac 50 to make-it a good 2X50W amp.
And i suppose we reached our goal, because it was my preferred amp during decades (despite grass is always greener elsewhere) and the guy witch had refurbished-it has published positive comments on its sound.
"When released in 1971, this unit which remained until the end the flagship of the manufacturer, was a racing car in front of witch very few American or Japanese amplifiers could compete.
Amazing performance (0.05% THD) instantaneous power 200W, volume controls and tone controls with switched fixed resistors, protection against overload, such were the characteristics of this amazing amp. This copy is one that my dad bought in 1973
"

and, in a mail to me:
"These amplifiers are still along the best I have ever been given to listen."

I was pretty proud of it :-)
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Old 3rd November 2012, 01:27 PM   #272
Bonsai is offline Bonsai  Taiwan
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I think modern CFB amps are a world away from the designs shown by ELvee above. And the topology is now underpinned by some serious math, which I don't think was the case back then. You may recall that CFB really took off in the mid 1980's when a slew of CFB op amps were released by the major semi companies. I still have somewhere copies of articles on CFB from EDN and the like.

But, I think all this discussion about CFB vs VFB will not lead to a clear conclusion. I have heard, and now built both topologies and it's quite possible to design good sounding amps of either type - different, but both sound great.
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Old 3rd November 2012, 02:52 PM   #273
Jay is offline Jay  Indonesia
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Originally Posted by ivanlukic View Post
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 was trying to point out that "good enough" is a relative thing. A young boy may come to this site telling that he has built a GREAT sounding one-transistor amp. "Great" here doesn't mean anything, because it is relative, probably relative to this young boy pocket radio.

Same with your statement that hexfet can make a "good" amp...

But my statement was: "I will and have assumed that IRF in class-B will never sound good enough". That because I have built many amps and that is my current statistics. Theoretically they have too high input capacitance.

"Good enough" also relative to other high quality amps that I have been trying to search and build. So if you think the A207 is good, that's a valid statement. But...

Quote:
Originally Posted by ivanlukic View Post
I know Stochino circuit and I do not think that building it would bring any real improvement in sound quality over Pioneer circuit.
What do you mean you "know" Stochino circuit? It is to me much much better than the pioneer. Like heaven and earth. Soundwise, and also in simulation (actually, Stochino amplifier simulated performance is very unique, rarely seen).
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Old 3rd November 2012, 03:04 PM   #274
MiiB is offline MiiB  Denmark
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I'am quite confident that both types of feedback can yield superior results... what could be interesting also to discuss is what kind of demands the two types put on the rest of the circuit.
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Old 3rd November 2012, 04:19 PM   #275
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Originally Posted by Jay View Post
I was trying to point out that "good enough" is a relative thing. A young boy may come to this site telling that he has built a GREAT sounding one-transistor amp. "Great" here doesn't mean anything, because it is relative, probably relative to this young boy pocket radio.

Same with your statement that hexfet can make a "good" amp...

But my statement was: "I will and have assumed that IRF in class-B will never sound good enough". That because I have built many amps and that is my current statistics. Theoretically they have too high input capacitance.

"Good enough" also relative to other high quality amps that I have been trying to search and build. So if you think the A207 is good, that's a valid statement. But...



What do you mean you "know" Stochino circuit? It is to me much much better than the pioneer. Like heaven and earth. Soundwise, and also in simulation (actually, Stochino amplifier simulated performance is very unique, rarely seen).

I mean I have seen Stochino schematics: fully symetrical circuit, very high slew rate, etc. But complicated for diy unless one has original pcb-s. I must admit that it would be very difficult to make single pcb just to try a circuit. Stochino is probably very good but I do not have pcb to prove it.
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Old 3rd November 2012, 09:30 PM   #276
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Bonsai/MiiB, I share your sentiment completely, neither CFB or VFB is better than the other. If both are designed with the same care and objective, they may sound very different or even very similar. for as many reasons/arguments as we can think of and put forward.

If there really did exist a BEST sounding design, then why do we not all own one.
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Old 4th November 2012, 01:22 AM   #277
Bonsai is offline Bonsai  Taiwan
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Quote:
Originally Posted by Nico Ras View Post
Bonsai/MiiB, I share your sentiment completely, neither CFB or VFB is better than the other. If both are designed with the same care and objective, they may sound very different or even very similar. for as many reasons/arguments as we can think of and put forward.

If there really did exist a BEST sounding design, then why do we not all own one.
Agree!
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Old 4th November 2012, 04:33 AM   #278
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Most studio and sound reinforcement power amps these days use complex fully symetrical circuits (a la famous Bongiorno) with great number of transistors. No doubt, these amps have excellent specs and sound very good, but simple CF design, such as Esperado did in 1971, still sound better, and that is what really counts. Sure, there is more of DC offset, but it could be tamed to safe levels.
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Old 4th November 2012, 05:45 AM   #279
Bonsai is offline Bonsai  Taiwan
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Quote:
Originally Posted by ivanlukic View Post
Most studio and sound reinforcement power amps these days use complex fully symetrical circuits (a la famous Bongiorno) with great number of transistors. No doubt, these amps have excellent specs and sound very good, but simple CF design, such as Esperado did in 1971, still sound better, and that is what really counts. Sure, there is more of DC offset, but it could be tamed to safe levels.
I don't think so.

The number of transistors in a circuit has nothing to do with sound. Take a look at an Accuphase for example. Many active devices in the signal
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Old 4th November 2012, 06:43 AM   #280
MiiB is offline MiiB  Denmark
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Then some may think that Accuphase is not really what makes you thick...
I'am 100% in favour of simple designs, or at least designs with a short and low component count in the signal-path...
I don't aim for low(ish) feed back, but I Do aim for feedback that add's in a dynamically linear way... hence my quest for the demands on the rest of the circuit. For current feedback CCS drive is in my book mandatory.
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