The cap between pin 3 and 2 on the pot isl how bright switches or bright channels are done in most all amps. Simple and easy to tag one on and see what happens. It may or may not be what you're looking for, but worth a shot. The fet buffer just gives a nice almost 4 meg load for passive input and Being single ended it's likely to have even order distortions, kinda, sorta, maybe almost like a tube would. Certainly prettier than an opamp buffer in that position. Really this thing would have no roll off in the audio band at all post the opamp amp stage. Try the cap/pot bypass with a mylar, mica or anything other than a ceramic. You can use the fender/alembic bright scheme as a guide, just scale the cap for the pot's value. Bigger pf brassier treble, smaller pf daintier treble. You other kids... don't try this at home.
