Found a bunch of Nine Volt Nirvana/Joe Gagan schematics on Fredd Brigg's blog. I'll probably do a few more of them, but first is the Tape Measure boost. Super simple and should easily fit in a 1590A. Original unit used a trimmer instead of an external volume control, but I figure most people will want the external control.
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.