I used to have a Peavey Classic 30 that had switchable distortion and reverb. However the included footcontroller lacked LED indicators to tell if the dist/reverb was on or off. There are LED-equipped footswitches on the market, and I even believe Peavey’s newer versions have LEDs.
Well, why spend money on a new switch when you could simply get into DIY-mode?
The circuit used here isn’t guaranteed to work on all amps, but if the amps uses relays for the switching, chances are this should work on other amps as well. Be sure to check polarity on the footswitch jacks.
The Peavey switch connects to the amp via a cable with two wires + what appears to be a common ground in it. However, the naked wire is actually the positive supply, and the two other wires supply current to the relays for distorion and reverb. Roughly like this:
So it’s really just two spst (1xon/off) switches that turn on the current to the relay coils. The key word here is current. The coils need a certain current to achieve a sufficient magnetic field an thus be able to move the mechanical switch in the relay.
Now, as I actually don’t own the amp anymore, I’m not that sure about the numbers here, but I measured the voltage from +V to coil with switch open, and I think it was around +30V. The more important thing however is the current, the currents were sligthly different for the two relays, but both were somewhere around 20-25 mA. I’m not sure how much the relays need, but this is important as the leds used were rated at max 30 mA, and now there’s no need to add series current-limiting resistors.
I opened the switch by removing the bottom plate. It wasn’t glued or anything, so a sufficient amount of brute force worked fine. The only thing I needed to do was to add LEDs in series with the switches. Like this:
The naked conductors need some sort isolation of course, normal electrical tape works fine.
Done!
As I sold the amp after finishing the mod, I never got to test it on a gig. But it worked just fine at home, and as long as the LEDs don’t fail, I’m sure it will go on working fine. (if a LED fails there will be problems, as they are in series with switches. But not harder to fix than replacing the LED, they are really cheap)
Update: part layout and schematic picture:
What's wrong with this circuit? 