This is a channel selector designed to work with Fender amps. I built it because my new Hot Rod DeVille, while a great sounding amp, has a serious limitation - all three channels share the same tone stack. Usually the settings that make for a good clean tone, don't work for the distortion sound, and vice-versa. This amp has a reputation for having a bad distortion sound, but the reality is that it just needs some proper EQ. The pedal I built allows me to put graphic EQ's in the effects loops for the Drive and More Drive channels, and have them automatically switched in whenever those channels are active. Now I get great cleans and great distortion sounds.
Below are the schematics of the stock Fender footswitch and my channel/fx loop switch.
Not a whole lot to see, but I think it's worth noting that both channels, along with the LEDs are controlled by a single signal. Clever, if a bit tricky to figure out. The key is that the driving voltage coming from the amp is an AC signal. By shorting or rectifying it the right way, the LED's are made to light up properly, and the resulting signal going back to the amp can be used to figure out which channel should be active. Honestly, I haven't bothered to work out exactly what's going on here, but luckily it's not necessary to understand the circuit if we simply wish to copy it.
My footswitch is basically the same circuit, though drawn slightly differently. The only real difference is that I replaced the single pole footswitches with 3PDT switches, and I'm using the extra two poles to switch the effects loop.
These are the 3 "new" effects loops. One for Clean, one for Drive, and one for More Drive channels. In my rig, the Drive and More Drive channels each have a graphic equalizer in their effects loops, while the clean effects loop has a complicated little setup that I'll have to describe somewhere else (basically a chain consisting of a splitter, distortion pedal, eq, volume pedal, and a mixer that lets me fade distortion into my clean sound).
I didn't use a circuit board. It was easier to just wire everything point to point. Notice I had to relocate the jack in the upper left corner because it interfered with one of the effects loop jacks. That was very aggravating, but sometimes one forgets to check the clearances when laying something like this out. It still works fine... it just looks bad. One of these days I'll get my hands on a label maker and fix up the outside. The sharpie tells me what I need to know, though.