The Seymour Duncan Pickup Booster offers 25 dB of clean boost with flat EQ (and it's also a line driver). It uses a combination of two NPN and one PNP transistor. Originals use BC107s and BC177s, but other transistors should work fine as well. Check out the demo video below for more info.
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.