Question about opamp circuits, too long to fit title field

[johanwastaken]

Basically I have made a tremolo LFO that uses an optoisolator to make the resistance across two pins increase and decrease in time with the LFO.

What I need is the option to let the increasing resistance either increase or decrease the volume of an opamp. The reason why I need this is that in a stereo tremolo, you either want the two channels to do have the same curve or you want the channels to have inverted curves.

Is there an easy way to toggle between these two things with a switch? Maybe switch the placement of the resistor between the feedback loop and before the opamp?

[earthtonesaudio]

Post a schematic if you want specific advice.

But until then, my advice is to make another driver for a second optoisolator that taps off the LFO. Check this out:
http://www.geofex.com/article_folders/p ... verser.htm

[johanwastaken]

Something like this is what I had in mind:


Since the gain is R2/R1, an increasing resistance across the optocoupler will decrease the gain. I want to be able to flip a switch so that the opposite will be true, that increased resistance across the optocoupler will increase the gain.

I could use a DPDT to simply swap them around but is there an easier way?

An extra optocoupler will use too much extra board space.

[johanwastaken]

By the way, there's an error in the schematic. The two lugs of the optocoupler shouldn't be connected.