Is the CFB topology superior, and why? - Page 22 - diyAudio
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Old 22nd October 2012, 08:09 PM   #211
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Joking...Impedances are up to you...
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Old 22nd October 2012, 09:15 PM   #212
wahab is offline wahab  Algeria
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Quote:
Originally Posted by Esperado View Post
You are right. Just increase those to 1.4K to push the driver quiescent to the same value than original and have a fair comparison ?
Too, i was wrong, telling that the Power Mosfets where IR, they where original Hitachi, i think. Time is so far away, when i constructed this amp and my memory burn-out with time to lower value.
A distorsion test would be interesting , just use whatever
soundcard you have , it will be enough up to a few Khz.

As spectral analyzer Visual Analyzer or RMAA should do it perfectly.
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Old 22nd October 2012, 09:16 PM   #213
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Christophe

Thanks wasnt sure.

I was just trying to show what is needed to have the same loop gain between the ltp and complimentary emitted coupled pairs.
This later cfa topology does allow one to theorectically zero out its distortion with emitter resistors to the feedback point.

Thanks
-Antonio
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Old 22nd October 2012, 10:05 PM   #214
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Quote:
Originally Posted by wahab View Post
A distorsion test would be interesting , just use whatever
soundcard you have , it will be enough up to a few Khz.
As spectral analyzer Visual Analyzer or RMAA should do it perfectly.
I believe in my old LEA. The original amp showed something like 0.008/9 % reduced by something i evaluate as a 10 factor with current feedback (needle was moving too much with the noise to can measure anything).
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Old 22nd October 2012, 10:24 PM   #215
wahab is offline wahab  Algeria
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Originally Posted by Esperado View Post
i evaluate as a 10 factor with current feedback
Such estimation cant be right as it involves one order of magnitude
better linearity , yet there is still two stages and the original Crescendo
already almost maxed out the THD numbers that are possible for two
stage topologies.

So either your amp has 20db higher OLG , wich is not the case
or the components did magicaly yield ten times better
built in linearity....
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Old 22nd October 2012, 10:40 PM   #216
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Wahab, as i said, it was too low to measure. The only thing i'm sure about is that distortion was decreased significantly.. I tribute-it to the speed improvement.
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Old 31st October 2012, 02:33 PM   #217
Elvee is offline Elvee  Belgium
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To close the subject, here is a final example showing how misleading preconceptions can be.

This output stage has performances that most aficionados would think as typical of CFB: sub-ppm linearity, output impedance in the microohm range, etc
Yet, it is a pure VFB, but more than that it is an absolute extremist of its kind: the feedback is 100%, and pure voltage mode, and the input by contrast is almost in current mode (sort of). In fact, the exact opposite of CFB.

Think about it...
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Old 31st October 2012, 05:05 PM   #218
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Replace Q8/Q10 by low Z resistances, and common base by common emitter for the input stage, what is-it ?
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Old 31st October 2012, 05:13 PM   #219
dadod is online now dadod  Croatia
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Non switching!
Haw about the bias, is it something close to the Edmond non switching auto bias OPS?
Could you give some more information?
dado
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Old 31st October 2012, 07:02 PM   #220
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by Esperado View Post
Replace Q8/Q10 by low Z resistances, and common base by common emitter for the input stage, what is-it ?
Apart from mundane biasing details, there is one big problem there: it will become a schmitt trigger due to positive reaction.
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Haw about the bias, is it something close to the Edmond non switching auto bias OPS?
I don't know, that is one of the many topologies I have investigated, I let you decide.
Quote:
Could you give some more information?
Maybe some day I'll publish a project
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