DC offset on the output should be about 2volt with that 100k:150k divider at the +input of the opamp.Leo..
To get max output swing, replace the two bias resistors with a trimpot. Adjust untill a ~4volt output signal clips symetrically.Leo..
Can be explained if there is someting wrong with the input caps on the pots.If there is a DC short/leak to ground there, then the opamp tries to compensate by increasing it's output.Did you connect the 10uF caps with negative to pot and positive to 50k resistor.Post a picture of the setup.Leo..
Hi,Can you change the values I have highlighted, and recalculate the 75K to give the gain you need with 4K7 or 10K input resistors.Place a 1uF cap from the junction of the two 10K providing the 1/2 Vcc, to gnd.10uF is too high for the high values of resistors you are using.Tom...
Also If I change the 50K into 10K each will it not adversely affect the channel separation?
It would actually be better to use 100k for that reason, althoughhigh impedances have issues with pickup and noise. The existing 50k seems like a not unreasonablecompromise.A better approach overall is to buffer pot wiper voltage with a unity gain buffer, then the summingjunction resistors can be a nice low (ie low noise) 1k or whatever. For a low noise microphone preampyou'd have to pay close attention to such issues, but that's not the case here of course.
Have you measured the BW?Tom.....