Just bought a new Yamaha TRB 1005 at GC. Nice bass, had it professionally set up, now it plays great! In the control cavity, there are two small pots on the board. Anybody know what these do? Nothing in the manual about these at all. The bass is active, so I assumed they'd be a midrange sweep/adjust or possibly an output control. I tried turning them and playing, but wasn't sure I was getting any results???