Got a couple SWAH boards because they sounded fun.
Set it up usable for bass, using notes from Barry and Cybercow dug up on the forum.
A few things to make note of:
1) in this instance, the effect chokes out when the sensitivity pot is turned past something like 9 o’clock. I assume it’s just too much resistance for some tolerance between components.
2) Cybercow was right, I do prefer it with red LEDs over 1n4148s. Only a little different, but it’s there–at least in this case.
3) My severely limited supply of 1n34 diodes is precious, and I cracked one testing this. Good news: a BAT42 also works just fine. Maybe even a little better, but I’m not sure how perceptible it is. The 1n34 Vf was measuring at 383, the BAT42 is measuring at 324.
I don’t know if these are consistent enough to suggest as a replacement, but they’re worth having on the list of things to test.

Included a Buff n Blend, because I made this one for my bass. Had to flip the board to get it to fit and run a bit of spaghetti wiring, but it seems to be working. R5 is currently a jumper, but it’s socketed.
The ‘Range’ switch changes C4 and C5 between 22n (stock) and 47n for the lower filter sweep. The 47n caps are in sockets, so I can change to 33n for a sweep between, or test even lower.