[sdiy] Blocking/Decoupling caps on a summing op-amp mixer

Justin Owen juzowen at googlemail.com
Wed Mar 19 10:44:08 CET 2008

From: "Justin Owen" <juzowen at googlemail.com>

> ...three schematics I had all showed polarised capacitors at each audio input (channel) with
the positive side facing towards the op-amp - so: audio input to negative side of cap to
(feedback?) resistor to (inverting?) input of the op-amp.

Huh . . . I think this description and the next are the same.

> Works fine - no probs. But then I found 3 new schematics - exactly the same layout - but
the caps have the negative side facing the audio input.

Duh - yes you're right -  my mistake.

The original schematics had the positive side facing the op-amp - the new schematics have the negative side facing the op-amp... But there's a few other things I missed after looking at it again this morning with fresh eyes and a little sleep !

Your answer (and everyone else) helped alot - appreciated.


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