Here's a very nice sounding British-style overdrive pedal from Boot-Leg Effects in Japan. It uses three-quarters of a TL074 quad op-amp, as well as germanium diodes (most likely 1N60s). Original units use an electrolytic 470n capacitor, but I've laid out the board for a film cap (though the PCB has pads for an electrolytic). I've also added a pull down resistor at the input and some extra power filtering. Here's a demo from another DIY builder.