Switching an effect on and off can be as simple or as complicated as you can make it. 3PDTs are pretty much the standard these days for true-bypass switching. However most of the 3PDT footswitches I've used make a lot of noise (not necessarily in the circuit, it's just loud when you step on them) and while that's not really the end of the world, it'd be nice to avoid the loud "KATHUNK" of the 3PDT. Relay switching fits that bill rather nicely, and there are lots of different ways to trigger the relay, some more complicated than others. In my search for one that was fairly simple and wouldn't take up too much room in a pedal, I came across this article from a few years back by Paul in the Lab. It uses just 3 transistors, a momentary switch, and a DPCO-type relay. I've drawn his circuit up for use with a board mounted SPST momentary off/on footswitch (if you need a perf layout, check out this one over on lvlark's blog). You'll need a 5 volt Omron G6S-2 relay (I got mine here), and a lot of different transistors can be used. BC547 and 557s are called for in Paul's schematic, but 2N3904 and 3906s or similar can be used as well. Most SPST momentary switches I found had the solder lugs on the side, so the board has been laid out to fit vertically in a pedal enclosure. Everything is mounted to the circuit board on the component side and the board is small enough to fit in a 1590B. Note: This has been updated to reflect the discussion below. Here's how the switch should mount to the board.
