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Old 4th December 2012, 08:58 PM   #1391
sonnya is offline sonnya  Denmark
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Quote:
Originally Posted by Esperado View Post
Can't you add a // cap with the feedback resistance to keep the closed loop bandwitch the same ??
For the quiescent, my amp use a ccs referenced to rail, so we are not in the same situation, you are right.
If it is okay, you can show me the circuit. Just so that i can follow you.
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Old 4th December 2012, 09:00 PM   #1392
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Quote:
Originally Posted by Esperado View Post
Can't you add a // cap with the feedback resistance to keep the closed loop bandwitch the same ??
For the quiescent, my amp use a ccs referenced to rail, so we are not in the same situation, you are right.
No as with rising frequence the cap will start act as a smaller Rf. And it currentfeedback this oscillation will start
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Old 4th December 2012, 09:02 PM   #1393
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Where is your schematic, for i can be more accurate ?
I know this amp is very sensible and each pole change can have a lot of consequences...
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Last edited by Esperado; 4th December 2012 at 09:04 PM.
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Old 4th December 2012, 09:04 PM   #1394
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http://sitosite.dk/amps/TSSA-01300712.pdf
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Old 4th December 2012, 09:17 PM   #1395
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Well, i understand better your choice, now. I would try a 2K for R11 - R12 and a little paralleled cap with it for stability and no overshoot on square waves, if possible.
The thing i worry, looking at your schematic is the one octave upper high pass filter frequency if we decrease the R13 -R14 from 100 to 50, right ?
You have better experience on it, anyway... I suppose you have tried near everything ?
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Old 4th December 2012, 09:25 PM   #1396
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Quote:
Originally Posted by Esperado View Post
Well, i understand better your choice, now. I would try a 2K for R11 - R12 and a little paralleled cap with it for stability and no overshoot on square waves, if possible.
The thing i worry, looking at your schematic is the one octave upper high pass filter frequency if we decrease the R13 -R14 from 100 to 50, right ?
You have better experience on it, anyway... I suppose you have tried near everything ?
You are right. I remembered wrong. It is 47pF millercaps. Withe 33pF we starts to have small signs of oscillation driving capacitive loads.
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Old 4th December 2012, 09:28 PM   #1397
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Originally Posted by Esperado View Post
I suppose you have tried near everything ?
There is always something new to try.

My problem is that my time flyes away. Right now i am doing a stepup LED driver for a new display for a customer as the OLD display was EOL!!! It is 23:37 .. stupid stupid .. When you can make audio instead....
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Old 4th December 2012, 09:36 PM   #1398
Salas is offline Salas  Greece
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So to put it in a nutshell, is George's move to go 50 Ohm +6dB worsening the stability or THD spec or does something else negative? He loses 6dB feedback and some damping factor is one thing I would suppose, but he drives a 20 Ohm+ load.
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Old 4th December 2012, 09:41 PM   #1399
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No it is not. It works very well. My protoamp has run for months with this configuration.

No need to worry.

By using 50R you do not lose feedback. Distortion is the same. Damping factor is the same.
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Old 4th December 2012, 09:48 PM   #1400
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Originally Posted by sonnya View Post
No it is not. It works very well. My protoamp has run for months with this configuration.

No need to worry.

By using 50R you do not lose feedback. Distortion is the same. Damping factor is the same.
You have to focus on the RF (R11 and R12) combined with the millercaps (C12 and C13).

They set the bandwidth. Do not place a cap across R11 and R12 . It will oscillate right away with a capacitive load.
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