Kevin,
i'm not really familiar with the Brown Bass, and I can't keep all the electronic variations straight... but I'm pretty sure that if you're looking inside the control cavity, at a couple of small blue cubes with a slotted white circle in the middle, then these are trimpots to adjust the gain of each pickup.
They have nothing to do with the filter(s). The idea here is that you can adjust the pickup heights (and angles, in various ways...) to suit your tone preferences, and then tweak the trims to balance the output levels of the two pickups in whatever way you might prefer.
Adjusting the gain of a pickup via the trimpot is exactly the same, in terms of tone, as adjusting a dedicated volume knob for that pickup, or turning the pan knob (depending on what you have). Changing pickup height and angle(s), however, will alter the sound in different ways, so it's nice to have this flexibility.
-Bob
(edited) PS - I have custom electronics, and my trimpots happen to be backwards (don't know if this is typical): the one closer to the bridge controls the neck pickup, and vice versa. But you can easily hear the volume change with less than a quarter turn, so it's not hard to figure out.
(Message edited by bob on January 04, 2004)
