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P-bass wiring, weird hum

Discussion in 'Pickups & Electronics [BG]' started by Fathand, Jan 20, 2012.


  1. Fathand

    Fathand

    Sep 24, 2005
    Finland
    Ok. I wired one of my basses with this setup:

    - Basic P-bass PU
    - 1 x Vol (250 pot)
    - Output

    All is otherwise cool, I'm getting a sound and the volume is working BUT I'm getting hum / noise which ends when I touch the volume pot and gets louder when I touch the poles on the PU. Is this a grounding problem, bad solder, broken PU or what?

    The ground wire is solidly attached under the bridge (I checked it when I did some maintenance to the bridge screwholes) and soldered accordingly to the same pin as the black wire from the pot and the ground wire from the bridge. I'm using the PU manufacturer's diagram (just bypassing the Tone pot, which I never use): http://www.teslapickups.com/wp-content/uploads/tesla_files/wiring_diagrams/bass/Standard-P-Style-Bass.pdf
     
  2. Matthijs

    Matthijs

    Jul 3, 2006
    Amsterdam
    Is there also humming when you're not touching the ground? If so: In that diagram there are two white wires coming out of one of the treble side pickup. Is the connection between the pickups pre-soldered or did you do that yourself? Try swiching those two wires, because the pickup may be wired non-humcanceling

    If the humming is only there when you touch the ground, and the wiring is as shown, it should hum just as much when touching the pot as when touching the strings connected to that ground wire. And it should not hum that much when you are touching the ground.

    Also check if the problem is only related to this bass, and not related to your amp and it's grounding.
     
  3. Fathand

    Fathand

    Sep 24, 2005
    Finland
    The other white wire is presoldered to the bass side, only 1 black & 1 white wire are available for soldering. It's always possible that the PU is wired wrong from the get go... I do have another P-pup, so if nothing else helps I'll switch the PU.

    it hums constantly, only stopping when I'm touching the volume pot. Touching the strings or bridge has no effect (the hum/noise continues).

    I'm using a computer + interface + preamp -setup, which is dead quiet with other basses. :)

    Thanks for the help!
     
  4. Matthijs

    Matthijs

    Jul 3, 2006
    Amsterdam
    O.K. I misunderstood, I thought the humming increased when you touched the pot. (that's why I asked about the amp).

    I'd think it would be pretty hard for them to presolder the pu wrong, but you never know.

    Your ground connection to the bridge is obviously not working, Probably a broken wire or broken connection. However: that will still leave you with a badly humming bass whenever you let go of the strings.

    How about the shielding: is there a shielded baseplate under the pu and is the control cavity shielded?
     
  5. Fathand

    Fathand

    Sep 24, 2005
    Finland
    Ok, so I'll have to check the ground connection again. There's no shielding whatsoever (but a lot of bare wood, because I've modded this bass pretty extensively over the years..).

    It had EMG's for years, didn't even need the groundwire during that time.. I'll go over it again and if nothing helps, I'll slap an EMG in again - no more problems. ;)

    Thanks.
     
  6. Go through your wiring very carefully - the diagram you posted looks perfectly OK. A few things to watch out for:

    - the casings of the pot(s) must be grounded
    - the wires from the pup(s) to the pots must be twisted together (yep, you wanna see how many people don't do this)
    - the wires between pot(s) and from the pot(s) to jack must be twisted
    - check you have the right connections on the jack (some are ealisy reversed - ensure you're using the ground for ground).
    - consider the pups are using American colours where white is "cold" (ground) and black is "hot" (I use loads of sensors from America and this catches me often!).
     
  7. Matthijs

    Matthijs

    Jul 3, 2006
    Amsterdam
    It's hard to tell how big your hum problem is. With passive pu's, even humcanceling p's, some hum is expected. Shielding should help a lot and would normaly be enough to make a P dead quiet. There are lot's of helpfull threads on that.
     
  8. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    I had a MiM P bass in for a setup yesterday. The owner complained about this exact problem. The bass had no shielding whatsoever, and the D/G pickup half hummed loudly if you touched the poles.

    I added some shielding under the controls and under the pickup, as well as replacing the cheap output jack. I only had a half hour to work on the bass because the guy had a gig.

    The buzzing problem was not fixed, but was a little better.

    I suspect it was largely from the non grounded steel poles on the ceramic magnet pickup. Steel poles will pick up a lot more electrical field noise than alnico poles.

    I'm going to do a few more things to the bass when he returns it.
     

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