P Bass HUM @ high tone setting

**frits51** · #1 11-24-2012, 08:19 AM

Happy Thanksgiving weekend to everybody. I've learned a LOT on these forums and I'm seeking to learn a little bit more.

2004 MIM P Bass w/ SD SPB-3. Just changed the stock bridge out for a Babicz. I have a Babicz on my Jazz and like it a lot (incredible sustain, great tone and adjustments are easy and precise).

I never noticed it before, but with tone knob fully in 'treble' position, I get a hum. Did I fail to make sure the new bridge was grounded? Well, I put alligator clip jumpers from string to string, then took the last jumper to ground (jack nut). No change. I measured resistance from each string to jack nut - got 0.1 to 0.2 ohms. I'm grounded!

I've had the bass about a week. Haven't opened up the wiring cavity.

The hum disappears when I grab a metal knob (tone or volume), also when I mute all strings with my left hand. Interesting note - muting one string with my left hand removes far more hum than muting one string with my right hand near the bridge. This probably doesn't mean anything.

I didn't notice this until I changed the bridge, but then I don't turn the tone knob more than half way up from the low side anyway.

Before I open the wiring up, I thought I'd give you all a chance.

Thanks,
Mark

Arvin · #2 11-24-2012, 01:01 PM

Quote:

Originally Posted by frits51

The hum disappears when I grab a metal knob (tone or volume), also when I mute all strings with my left hand.

You've got a grounding problem. Check your ground wire connections at the bridge, the backs of the pots, and the output jack sleeve. If those connections are solid, the problem is most likely that your outlets are not properly grounded.

I hope it's in your bass; the house grounding issue is a bigger fish to fry.

gunlak · #3 11-24-2012, 01:06 PM

his ground is fine. he needs shielding on his bass

**frits51** · #4 11-24-2012, 02:48 PM

I'm leaning toward grounding. Not at the bridge... I've already tested that.

I'll have to open up the wiring cavity and check grounding there. When I re-did my Jazz (series-parallel switching, Bourns blend pot), I did the grounding in a star fashion. Jazz is quieter than ever before.

I may end up doing the same with the P. I'm open to shielding... but only if I have to.

Thanks, guys.