DIYStompboxes forum member Ripthorn adapted the Alembic F-2B tube preamp to a JFET preamp. It gives you 3-band EQ controls, master volume, and a bright switch. Fairly simple circuit, but might turn into a bit of a rats nest with the offboard wiring (I know, a bit out of character for me). Set the trimmers to about 4.5-5v and then adjust from there to taste.
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.