volume pot wiring

Is it in a passive system? Active? Same question to as far as pickups and are you using 250K or 50K audio or linier? Maybe you choice of pot (no pun intended) isn’t the right match?

I have had on occasion ran into a few bad pots but not often and not 2 in a row.

 

Totally normal for a passive 2-pickup system. The best sound on a Jazz is to roll the volume off slightly on one or the other pickup. (If the volume drop is DRASTIC then one of the pickups might be wired backwards.)

If that bugs you (I think it's pretty cool ), you might invest in an active preamp.

 

Have your luthier friend check it out.

 

Another way to solve the issue is to put a .01 inline capacitor between the bridge pickup and its volume control. This cuts the extreme lows (which, being a bridge pickup, really aren't there, anyway) and cleans up the bottom end to get rid of impedance, phasing and comb filtering issues.

I've used this to great success since I figured out J-bass pickups do this decades ago.

 

I've had passive basses with 2 volumes do this,IMO it's the nature of running two pickups in parallel. My guess would be impedence loading when both pots are full onis whats happening. +1 active electronics would help.

 

JJ cancels noise/hum when the two pickups are at full volume; this necessarily cancels some musical information as well. The loudest/most aggressive sound is achieved when the pickups are slightly unequal and the cancellation is reduced. That's the clearest explanation I can think of.