Seymour Duncan Bass 400 Gain?

[glebert]

I bought this amp as a fixer, the power switch was shot, and now it is working. It sounds pretty good, but it sounds pretty weak until you have the volume almost maxed. When I use weaker PUP basses it seems like there is no way I could get stage volume output. Kicking in the Lo and Hi contour switches does help a lot, but to me those shouldn't be necessary to get full output, but wondering if others have experience with this amp. I can't find a schematic for the preamp, but since everything seems to be working I don't even know if anything is broken.

TIA,
Greg

[g1]

Schematics near the end of attached manual
(edit, I see what you mean, no preamp schematic)