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P Bass HUM @ high tone setting

Discussion in 'Pickups & Electronics [BG]' started by frits51, Nov 24, 2012.

  1. frits51

    frits51 Supporting Member

    Apr 30, 2011
    Heath, Texas
    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.

  2. Arvin

    Arvin Underwound Supporting Member

    Sep 26, 2008
    On the bench
    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.
  3. gunlak


    Nov 24, 2009
    his ground is fine. he needs shielding on his bass
  4. frits51

    frits51 Supporting Member

    Apr 30, 2011
    Heath, Texas
    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.