Remote reverb expression pedal

[fryingpan]

I'd like to be able to implement a remote reverb expression pedal, to tie in with the "reverb" pot on an amp I'm designing (slowly but surely). I don't want to send audio signals all the way to the footswitch and back, so this calls for a VCA, I suppose. Are there any parts that can work as a mixer (2 in, 1 out) that I can control with a control voltage? At that point I only would have to send V+, V- and CV at the expression pedal. I would also like to add the capability to set a minimum and a maximum mix ratio from the amp panel (I suppose I could do that with some pot wired as a voltage divider). Maybe a digital control would be easier but I'm not sure about that, as I'd have to include a microcontroller, clock and design the circuit so as not to make them interfere with the rest of the circuit.

[idy]

Another (simpler?) approach would be to use a vactrol (LED and LDR) with a control voltage going to the pedal, which dims an LED and changes the resistance of the LDR. Then a matter of setting max and min brightness, and using series and parallel Rs to determine max and min R of LDR (can also audition various values of LDR). Pretty easy to try out...

[ElectricDruid]

A vactrol is a good idea. Dead simple and reliable. The limitations are that you might struggle to get it to go completely to "off", and vactrols don't respond super-quick. But for an expression pedal, there's no way on earth you could flap the pedal faster than the vactrol could change value, so that's a non-issue. So it'd just be a question of finding a good balance of resistance to get the range you need.

[PRR]

IMHO, the LM13700 is a way to go. The clean input level is very close to what you get directly from a reverb tank (no input attenuating network). At medium and higher currents the OSI (hiss impedance) is very suitable. Eyeballing, a 10k load to Vref gives a useful amount of gain, the EF can buffer that as needed. Gain control can be 50k pot zero to +9V and 27k resistor wiper to Iabc pin.

Altho personally I've never used reverb as a fine-trim. None, barely-there, and SURFSUP!: three settings, and I'd usually know which when I walked into the place. Which really goes back to how it is usually done: knob on amp and a foot mute.