Jazz bass hum help

Before buying anything too expensive, look into shielding. Fender does very little shielding of their instruments.

 

I think I will get the same problem since I plan to insert a P-bass pickup in my Jazz bass, I have to make more room inside and will thereby destroy the existing shielding. My 1978 Precision seem to be painted with some kind of conducting paint inside, and connected to ground. But where can one find that kind of paint?

On my Jazz I get a considerable decrease of hum when turning up volume on both pickups due to hum canceling (I suppose), could it be something that is not connected correctly inside your bass? Due to Wikipedia cancellation is achieved by having "the coils in series and out of phase", mixing the wires puts them in parallel increasing the hum, or am I wrong?

 

That's not correct. The hum goes away when you turn the tone down because the EMI (electro magnetic interference) is being shorted to ground. There's nothing wrong with your tone control or tone pot. J-basses are only hum cancelling when BOTH PICKUPS ARE ON. Unfortunately, what you're experiencing is single-coil hum and it can't be completely eliminated. Shielding can help, so can proper grounding of your electrical system (it should be properly grounded anyway). Neon signs, flourescent lights, CRT monitors and so forth are bad sources of EMI and sometimes they are just unavoidable at a gig.

The best solution for me is any type of double-coil humbucking or hum-cancelling pickup, they sound fine to me but some people prefer the "true single coil" tone.

 

Yes second the EMI. Sometimes under certain lighting a single coil bass will hum like that especially when the tone pot is all the way up. The only true solution is to put different pickups in it. Sometimes you see and additional ground wire placed from the tone pot but I not sure exactly where they ground it to.

 

Had pretty good luck just sheilding the inside of the J pup covers. Don't pick up the local radio station any more either and get solo the bridge without hum.

 

+1.
Sounds like a textbook case of EMI. Shielding does help with that.

 

Is your bridge connected to ground? On one of my basses I've noticed that I can reduce hum with the tone as you explain (even if the volume is at zero on both pickups) but when I touch the strings it seems that the same hum is reduced that way instead