Not quite a Fuzz Friday, but a Filter Friday I guess. Goes hand in hand with some fuzz though. The Sound Saw has two different passive filters selected by the Channel footswitch. The filters then share a 2-transistor gain recovery stage. Here's the schematic for reference. You can use a common cathode LED for the Channel switch or 2 individual LEDs if you prefer. See wiring diagram below. Laid this out for a 125B, but should be easy enough to adapt for 1590BB if you prefer. Will probably be doing a fabricated version of this in the near future as well.
Sound sample:
Sound sample: