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Old 3rd January 2013, 08:13 AM   #3721
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Happy New year to you L.C. I hope this year will be full of splendid AUDIO projects as your SSA was.
I wanted to make a sim with your version of SSA, and asked your sim file for that. But my message had no answer. Anyway, this exploration is not a surprise for you, if you had read your private message box recently :-)
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Old 3rd January 2013, 07:52 PM   #3722
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Hi Esperado

OP amp kind of error correction is actually working as OLG of the corrected amp would be much higher, it certainly can lower distortions if stability maintain unaffected. Most probably OP amp will drive the feedback signals into peaking and even into oscillations if original amp could not follow.

What VSSA in other thread surprisingly showed me is its enormous damping (extremely low Zout) gained from high OLG/bandwidth and exact feedback/compensation scheme. uV feedback precision coming out of six transistors only makes amplifier's output differentiating from unloaded conditions down to few mV.

Square waves misuse showed no instability and for me that is of more importance than mostly accepted low THD/TIMD.

Regards, Andrej
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Old 3rd January 2013, 08:46 PM   #3723
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Quote:
Originally Posted by Lazy Cat View Post
OP amp kind of error correction is actually working as OLG of the corrected amp would be much higher, it certainly can lower distortions if stability maintain unaffected. Most probably OP amp will drive the feedback signals into peaking and even into oscillations if original amp could not follow.
Yes it increase the ratio of feedback as much as you can afford keeping the stability. (Phase margin can be unchanged, and even, we can be increased with some compensation caps in the error feedback loop, without affecting slew-rate of the power amp itself.).
About speed, the problem with fast power amp is to find an OPA fast enough, as SSA is damn fast itself. . No risk, in my example, to saturate the OPAs, the output of the second OPA stay at <+/-700mv peak at 100Khz full power with distortion at -60dB.
I do not know if it improve the sound or not: Need a try in real world. May-be the benefit will be side of the damping factor ?
As it is simple, easy and not expensive nor destructive, it deserve a try.
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Last edited by Esperado; 3rd January 2013 at 09:06 PM.
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Old 3rd January 2013, 09:47 PM   #3724
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I think this idea is pretty cool. I would love to see a real world implementation.
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Old 4th January 2013, 01:04 PM   #3725
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I think a more effective way of reducing distortion would be to use drivers for the LFETs.
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Old 4th January 2013, 01:38 PM   #3726
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Quote:
Originally Posted by keantoken View Post
I think a more effective way of reducing distortion would be to use drivers for the LFETs.
I think reducing distortion of the open loop of an amp is not to be opposed to the use of feedback, they are complementary. if you can reduce closed loop distortion while keeping the slewrate with a driver (i doubt) the error correction add will reduce the new distortion with the same 10 ratio.
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Last edited by Esperado; 4th January 2013 at 01:43 PM.
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Old 4th January 2013, 02:26 PM   #3727
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So the point is to decrease distortion without impairing slew rate?
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Old 4th January 2013, 02:31 PM   #3728
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Very nice Esperado :-)

I am working on a new amp (100W CFA) and after this will do another amp with AFEC (switchable!). I think the technique has merit, but of course you have to take care with the loop compensation. The free DC offset control is also a great side benefit!
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Old 4th January 2013, 03:41 PM   #3729
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Quote:
Originally Posted by keantoken View Post
So the point is to decrease distortion without impairing slew rate?
Well, something is interesting, below your question.
Because we increase the error feedback level, in a way, we reduce the slew-rate/correction-signal ratio.
But, because we are dealing with a yet low distortion, and because we can filter extreme HF from this added part of feedback; i believe we do not have to fear any added TIM.
So, the main benefit is to improve distortion on an EXISTING amp without modification of the amp Itself.
As noticed by L.C. an other approach is to increase OLG of the amp, not so easy while keeping-it stable.
This error correction present, of course, some negative aspects: it is a little acrobatic and need precise fine tuning.
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Originally Posted by Bonsai View Post
Very nice Esperado :-)
Even if i had this idea long time before, while i was working to my protection system, i forgot-it with time and it was YOUR publication which refreshed-it in my mind. So all the credit is for you.
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Last edited by Esperado; 4th January 2013 at 03:47 PM.
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Old 4th January 2013, 03:57 PM   #3730
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But you are not filtering extreme signals from the opamp. Any input/feedback signal regardless of BW will enter the opamp's output, no? Does the simulator model the effects of opamp output impedance?
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