Out of phase pickups?
 

I have a Jazz-style bass with the standard two-volume/one-tone control.

When both pickups are on full, no problem. When either pickup is turned completely off, no problem. When the bridge pickup is turned down gradually, no problem. However, when I turn the neck pickup down slightly, the tone becomes thin and nasally. It sounds as if the pickups are out of phase.

Based on what I have experienced, if pickups are out of phase, the sound is thin when both pickups are on full.

Any ideas?

Thanks.

It sounds more in-phase when they are both on full because one pickup is louder than the other. Neck pickups are generally louder on a Jazz bass. So both on full is not an even mix of both pickups. When you back one down so they are even, you can hear they are out-of-phase.

How do you fix this?

Reverse the hot and ground on one of the pickups.

i dunno, if they were actually out of polarity the bass would sound pretty bad with both pickups full-up.

i almost suspect a bad neck volume pot, or maybe something mis-wired.

Not if they are unequal volume, which is often the case. In most cases you have to back one pickup off a little and then it gets thin, which what he described.

I've had this happen to me many times.

@OP If you are unsure if its the pups or the pot/wiring, you could also test by rewiring the Neck pup to the Bridge Vol and the Bridge pup to the Neck Vol.

If the results are the same then the issue is from the pot/wiring, if the results are now switched, then its from the pups.

If pups, as SGD luthier said, you could always switch the hot and ground of one pup to test.

Thanks for the help. I had the wires switched and everything works great.