I thought I wanted a circuit that was a basic pan control, but after mapping it out it isn't so standard after all. The final design will have this exposed: two mono inputs (left and right), one stereo output (left/right), one pan/balance control. When the pan/balance control is set to 50%, one mono is 100% on one side, 0% on the other side. The other mono does the same but on the other side. As the knob is turned to one side, that side gets quieter and the other side louder until only the other side can be heard. Here is a table of what I am looking for. The question is how do I make a circuit to do this?
So some more info. This circuit is going to be used with my high-end Amateur radio that has two bands (think radios) built into it. These are the two inputs. I will be using headphones and monitoring two different channels at one time. When I need to focus on one band I want to be able to hear it on both ears.
I posted the same question in an Amateur Radio group and someone there said he will work on a circuit. I shared the design below with this person. This person liked it and added a wise requirement:
I would prefer full isolation between the two inputs. A traditional balance control provides some amount of output from one radio TO the output of the other radio. I would be happier if a signal wasn’t going into the output of my expensive radio, just to be safe. It’s not hard to do.
So the gentleman on Facebook has come back and added a bit, first canceling what he said above and then bring up an interesting point about how it would sound:
Alright I was thinking about this more. The responder to your question on StackExchange is correct - you don't need to do any further isolation because of the "virtual ground" at the "-" input to the op-amp. I think the one remaining question is how to get a response that's more pleasing to the ear (logarithmic). A pair of linear pots are going to hard to use, especially if they're ganged together. If you keep them separate then you could use "audio" pots. But I think there might be a tricky way to get a near-logarithmic response from linear pots.
Is there such a thing as a dual logarithmic center-tap POT?