mixer circuits

  
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The only downside to a single opamp stage is that it inverts the signal so needs another inverting buffer to put it back again (if absolute phase is important to you). I have seen bunch of schematics with both configurations but I don`t know which one would be the better design (i. e. is it better to put the volume pot before or after the opamp ) I have also seen schematics where the volume pot in the feedback loop
mixer circuits - schematic

of the opamp but I think I read somewhere that that configuration is a bad idea since it can introduce additional noise. From a purely theoretical point it has to be better to put the volume control after the opamp because then you are attenuating all the noise/hum/hash as the volume is reduced. Putting the volume control in the feedback loop is an absolutely valid method and can form the basis of a very high quality active volume control but it has to be done correctly for the best results. Choice of opamp is important and so to is ensuring that no DC current flows in the wiper of the pot. Doug Self used that approach in his precision preamp using two opamps per channel. You won`t find a better example I suspect.



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