Here's an other heavy one. This one was designed by Martin (aka soulsonic) and is basically 3 transistor stages and a tone stack into a JFET gain recovery stage. The toggle switch selects between distortion and fuzz.
The tone in Distortion mode is a big heavy, "Doom-y" sort of thing with alot of sustain. In Fuzz mode, it's a fart-y ripping sawtooth fuzz that's good for single-note lines and possibly bass, but it can do chords without totally falling apart.
The Contour control adjusts from a dark, low-mid-heavy tone when counterclockwise, to a scooped tone when clockwise. Around 12 o'clock it has a bit of a mid-peak.
Schematic and demo can be found here. I added a trimmer to bias Q4 (J201 or 2N5457 would be good subs). Should fit nicely in a 1590B.
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.