On every two PU bass I own there is a slight volume drop if the bridge is on all the way. It's not huge, but is clearly noticeable. Some kind of phasing (likely not the right word) of the two together maybe.They can make one pre-drilled body(IV's)simplier and charge for 2 pup's(which costs them very little)then the end user can turn off* the superfluous[bridge]pup.
Strangely, if I turn on the bridge pup, my volume decreases. Tone stays about the same. Bad pot? IDK-or GAS. I was f---**ing around with it at a recent gig to see what it did to my sound. Nothing useful.
*or remove-like Kat
**ool
