Last night I built an A/B box for my guitar setup (to switch between two signal paths, usually effects->Amp A/Amp B or Guitar -> Signal Path/Tuner. It was a first little foray to see if I could do something like this. It worked out pretty well – I got a diagram from www.fulltone.com and pretty much copied it – I got most of the parts from pedalparts – although with the exception of the 3pdt switch you could get them all at frys for about $15. if it’s not plugged in to power, the LED’s don’t work, but for some reason, the power seems to add a tiny bit of noise. I’m not sure why yet.