Question about ground noise

Discussion in 'Pickups & Electronics [BG]' started by pbassist, Mar 16, 2010.


  1. pbassist

    pbassist

    Nov 2, 2008
    Hi, from a few days I've starting to get ground noise from my p-bass special. The noise comes an goes, and usually it goes away after giving a few small hits to the potentiometers.

    I removed the pick guard in order to see if some soldering is in bad shape, and everything looks fine. Then I put a cable between the two volume pots and the noise was gone.

    So soldering a cable between the two potentiometers grounds is this a good idea? Can it do some harm to the bass or the amp? In the original schema http://www.fender.com/support/diagrams/pdf_temp1/basses/0135700_02B/SD0135700_02BPg2.pdf this is not done. Or should I get new pots?

    Another question? why is needed connecting the mass to the body of the bass (point 18 in the above schema). My bass only has around 1*1 inches of shielding paint, and I measured the resistance between the ground wire and the shielding paint and it was infinitum.

    Many thanks (and please excuse my bad English).
     
  2. slyjoe

    slyjoe Supporting Member

    Jun 28, 2008
    Valley of the Sun (AZ)
    The grounds are now connected better than only through the foil on the pickguard.

    Yes - it fixed the problem, right?

    It won't harm anything. You don't need new pots unless they aren't behaving. This sounds like it was a poor ground problem. You probably could have fixed by tightening the pots to the pickguard.

    A shield needs to be connected to the circuit ground. That is what the connection is doing. I don't think the shielding paint is doing much if there is only a square inch of it. And if the resistance is infinite, it definitely is not doing anything - the resistance should be zero.
     
  3. bassbenj

    bassbenj

    Aug 11, 2009
    Yes a wire needs to be soldered between the pots. ALL of the pots! The reason is that the pot backs are just crimped on. And there is the possibility that they can come loose and not make a good contact. When the crimp is good that back connects to the shaft that mounts on the plate and that grounds it all. But as you can see you have two groups of grounds. One group goes to the jack and one pot. The other group goes to the pickups and the other pot. If one of the backs gets loose or corroded and loses contact, you lose half the grounds. So don't rely on the pot back crimp to make contact. Run a wire down the backs of ALL the pots.

    As for the body ground. That is to ground the conductive paint in the cavity. This is VERY necessary for the shielding to work. Your paint may have a non-conductive overcoat so to test for ground you may have to scratch through that. The paint (or foil) should coat the whole inside of the cavity. Also there should be foil on the back of the pickguard and that should ALSO be grounded to the same place as the paint! Run a thin wire from pt 18 up and around one of the screws on the pickguard where the foil is so when you screw it down it mashes the wire against the foil. OK?
     
  4. pbassist

    pbassist

    Nov 2, 2008
    Right, just removing the pots , cleaning the rust of the part that makes contact with teh PG and putting them on again fixed the issue.

    About the shield, my bass is MIM so I'm guessing they didn't did a good job here... I also guess that I would need to get some cooper tape (is there much difference with aluminum tape? I can't find the cooper one in my city) and fix it on my own,as each time I come close to my computer I start to get a lot of buzz (this is very noticeable with the single coil, although the split coil also gets a bit).


    There is not any foil from the pg, but I have an gold anodized aluminum one, so I guess is not necessary. About the grounds... all the ground points are really the same in a bass, right?

    Yes, using a wire for connection the pots shield seems a more reliable way.

    Thanks for the help.
     
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