Project files for the Go! Booster. Note that the template in the board file is for the standard drilling that I use - you can ignore it, as it's not a visible layer for the sake of board export or manufacturing setup.
Hopefully at some point I will remember to upload an offboard wiring mini PCB for the 3PDT switch you will need.
The 3mm LED in the opamp feedback path will add some clipping; a heavy clipping diode like a germanium diode might cause too much signal loss, so if you're going to experiment, then socket the diode.
I personally tend to leave it blank; the production Go! doesn't have anything in that spot.
Finally, obviously you can wire the treble control up to an actual pot. This PCB should just about fit in a 1590A, but I choose to put it in a roomier 125B as I prefer the form factor.
Happy hacking!