I've been trying to create a balance control circuit for two audio channels. I'm finding it extremely difficult. I'm very adamant about a single knob controlling both the left and right balance while the center being even.
I've tried a bunch of voltage dividers using log pots, linear pots, dual dang pots, etc.. But I just can't quite get the behavior I'm looking for. It doesn't have to be perfect, just passable as an actual balance control. I find that it's very easy to get 1 channel to pan quite well from the center, while nearly impossible to get any sort of "near" linear panning from the other channel (this was mainly the case with dual-gang log pots). Another huge problem I have is setting the middle of the potentiates rotation as full amplitude for each channel.
I've recently considered using two MOSFETS/BJT's (one each channel) as some sort of variable attenuater each controlled by a voltage from a potentiometer (or a resistance from a dual gang potentiometer) but I began running into the problem of how to prevent one channel from being amplified while the other channel is attenuated. I cannot amplify the original signal very much (I can, but just a little) due to the fact that the output of this balance control circuit is the input to a class A amplifier circuit thats biased with 5V with a gain of about 13. I'm worried that if I amplify one channel due to balancing and then try to amplify I could exceed my voltage swing and cause distortion.
I asked a much vaguer version of this question earlier which ended up yielding a design that would work with well with the B5 (maybe B4) taper of this potentiometer series: http://www.bourns.com/docs/Product-Datasheets/pdb18.pdf This works well creating two voltage dividers by connecting the 3rd terminal to ground but I couldn't find either of those models for sale online anywhere. Unfortunately this means I can't actually use this solution to my problem.
Lastly, I'd prefer to not use a microcontroller if at all possible. I want to print my amplifier circuit to a PCB at some point and I wouldn't want to have to interface it with anything.
I realize there's a fair amount of distortion even in the second graph I posted, but this is only when the volume is maxed by setting Rp1/Rp2 to 0. I'm still tuning the circuit. But obviously there's a serious difference between with the second source connected and disconnected. Any ideas why?
Obviously nothing is perfect, the main thing that I NEED is at 0.5 rotations of the potentiometer, I need the dB loss to be -3 or less. From there on out of course I'd like the "ideal" balance control curve, but I'm really just trying to find something that works well enough that isn't too difficult to implement.
It's also entirely impossible I have no idea what I'm talking about and this is a horrible curve for a balance control, so feel free to call me out if that's the case. I'd rather that than build the thing and have it be.. not so great.
Thanks for any help in advance!