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Opamps as low Z buffers
Opamps as low Z buffers
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Old 6th November 2019, 09:05 PM   #11
PRR is offline PRR  United States
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Yes, there are many ways to shave a cat, and this one may not be best.

_I_ like a big capacitor(s) right ON the rail. Most chips (and many discretes) have falling PSRR at high frequency. Caps filter better the higher up you go.

If stuff stays class-A and modest power, I've had happiness with simple C-R-C-R-C filtering. Big caps are cheap now. Set the main corner far below the audio band and 120Hz will be teeny; also wall-voltage variations are reduced to sub-sub-sonic bobble instead of thumps. (No thump if you favor regulated bias reference or bipolar supply.)
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Old 6th November 2019, 10:33 PM   #12
Rick Miller is offline Rick Miller  United States
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Quote:
Originally Posted by PRR View Post
Yes, there are many ways to shave a cat, and this one may not be best.

_I_ like a big capacitor(s) right ON the rail. Most chips (and many discretes) have falling PSRR at high frequency. Caps filter better the higher up you go.

If stuff stays class-A and modest power, I've had happiness with simple C-R-C-R-C filtering. Big caps are cheap now. Set the main corner far below the audio band and 120Hz will be teeny; also wall-voltage variations are reduced to sub-sub-sonic bobble instead of thumps. (No thump if you favor regulated bias reference or bipolar supply.)
How big a cap are you using on the rails?

I also like RC filters. I use one or two sections of them before the regulator to try and lower the ripple and harmonics as much as possible in the space I have. No need for the error amp to deal with all this stuff if we can lower it before it gets there.
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