I recently stumbled on this set of schematics, it's the well known Pearce Bass amp from the early 90's,
http://web.me.com/travishartnett/Pearce_Amps/BC1_B2P_Documents.html
I posted it because it has a split channel with a distortion blend.
Included in the schematics are the Billy Sheehan (of Niacin) mods.