The Crowther Prunes & Custard is a unique distortion box good for both guitar and bass. It's a two-stage circuit, built around a TL072 dual-opamp. The first stage acts as a preamp, and the second stage generates the distortion, with harmonic overtones. I've laid this out for on board pots (long leg PCB-mount pots will probably work best mounted from the component side) and it should fit nicely in a 1590B enclosure. The 2 switches are SPST.
This is a library of perfboard and single-sided PCB effect layouts for guitar and bass. I'm not an electrical engineer by any stretch of the imagination, just a DIY'er who likes drawing layouts. It is meant for the hobbyist (so commercial use of any of these layout is not allowed without permission) and as a way to give back to the online DIY community.