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Old 3rd May 2013, 04:59 PM   #11
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In this circuit bypass caps increase open loop gain, more feedback, less
total thd. The Source resistances suppress the differences between N and P
channel, so greater 2nd/3rd with bypass caps.

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Old 3rd May 2013, 05:07 PM   #12
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I'm getting less h3 with cap but more h2 - can that be due to more olg, more fb effect ?

Also the outputs here were both n channel (post 8) but I don't think that changes your conclusions any
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Old 4th May 2013, 02:19 AM   #13
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I guess you would need to post the schematic, but I still expect that there
is asymmetry in the circuit being suppressed by the Source resistors.

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Old 4th May 2013, 04:51 AM   #14
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Your guess is right i reckon - i did not match the fets nor trim h2 at all so theres likely assymetry between top n bottom halves.

The schem - is roughly the one here with source resistors and irf outputs: The Valorous Amp - A modest aggregation of pass inspired ideas
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Old 4th May 2013, 01:48 PM   #15
6L6 is offline 6L6  United States
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Quote:
Originally Posted by Nelson Pass View Post
In this circuit bypass caps increase open loop gain, more feedback, less
total thd. The Source resistances suppress the differences between N and P
channel, so greater 2nd/3rd with bypass caps.
So is the apparent decrease in distortion a function of the cap doing something to the circuit's linearity,
or just because of the increase of total feedback?
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Old 4th May 2013, 02:22 PM   #16
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The reduction in H3 is likely increase in feedback. The relative increase in
H2 is likely decreased symmetry without degeneration.

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Old 3rd March 2014, 06:55 PM   #17
JZatopa is offline JZatopa  United States
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I know this post is a bit old but I am curious what the outcome would be if your test circuit had a p3 to balance the distortion after the additional caps.
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Old 4th March 2014, 01:01 AM   #18
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P3 can null out H2. So the combined effect of a P3 and bypass caps should be further reduced THD numbers.
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Old 4th March 2014, 04:50 PM   #19
JZatopa is offline JZatopa  United States
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Thats what I was thinking. Did you end up trying that and recording the results?
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Old 5th March 2014, 12:58 AM   #20
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sorry can't help there - I don't have a live F5 handy. I think i caused some confusion - the title of this thread was intended for the sim example shown earlier on. The measurements were done on another push-pull amp (see post 8). Nelson in post 16 explains the results nicely and I agree completely.

All that said, i have been using the bypass caps for some time and love them. I drop the loop feedback a touch as well while i'm at it. Opens up the sound a lot.
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