How to find source of grounding buzz

Discussion in 'Pickups & Electronics [BG]' started by socialleper, Nov 5, 2017.


  1. socialleper

    socialleper Bringer of doom and top shelf beer Supporting Member

    May 31, 2009
    Canyon Country, CA
    I have a set of DiMarzio DP126 PJ pickups that I just migrated back to a bass that had some SD QPs in it that I didn't like. Usually the DiMarzio pickups are dead quiet, but now that they are back in this bass I am having a grounding buzz issue. If the bass just sits on my lap, there is a faint buzz, but if I touch the metal parts of the bass it stops. I've re-soldered the grounding wired from the pickups three times now, so I don't think that is it. There seems to be a lack of how-to walkthroughs for finding exactly where the ground problem is happening on the internet.
    It is an all passive bass, set up Vol Vol Tone, with a on\off switch for the P and J. The buzz stops if I touch the strings, tuners, bridge, and knobs, but not if I touch the switches, and it buzzes a little more if I touch the pole pieces while not touching anything else.
    There must be a way to use a multi-meter to check the electronics of a bass for proper grounds. Can someone please help me with this?

    Update:
    Allow me to clarify something: These pickups were completely silent in this bass a few months ago and in another bass just moments before I removed them. They are humbucking. I either installed them wrong or damaged something. This is not a typical 60 cycle hum\RF problem. I am looking for advice on how to determine what I did wrong and correct it.
     
    Last edited: Nov 6, 2017
  2. socialleper

    socialleper Bringer of doom and top shelf beer Supporting Member

    May 31, 2009
    Canyon Country, CA
    Here is a picture of the body cavity.
    20171105_161817.jpg
     
  3. Take your ohm meter, set it for x1 range, and measure continuity between the bridge and the output jack sleeve ground. You should have 0 ohms, or at worst, a fraction of an ohm.
     
  4. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism

    Your issue is not a grounding one but a shielding one, your bass is getting RF interference. The fact the hum stops when you touch metal indicates this. The buzz you get when you touch the pole pieces is a grounding issue, that is why the noise gets louder. That can remedied by grounding the pieces or painting over them with clean nail polish, whichever you prefer. Everything I know on shielding can be read in the link in my signature. There is another great guide stickied in the repair forum. I have linked a thread below on grounding the pole pieces. If you want to test with a multimeter, check the resistance at your jack and the bridge/strings/knobs. You will find that your resistance is considerably higher than 0.1.

    I hope that helps.

    Pole Piece Hum: A Grounding Tutorial
     
    mikewalker and InhumanResource like this.
  5. socialleper

    socialleper Bringer of doom and top shelf beer Supporting Member

    May 31, 2009
    Canyon Country, CA
    It is about 0.3.
     
  6. socialleper

    socialleper Bringer of doom and top shelf beer Supporting Member

    May 31, 2009
    Canyon Country, CA
    These are humbucking pickups. As I said before, they were dead quiet before.
     
  7. Killed_by_Death

    Killed_by_Death Snaggletooth Inactive

    Once upon a time I had a Fender Blacktop Precision with double humbuckers. It buzzed like mad before I shielded it:

    IMG_20151224_205119-TB.jpg
     
  8. socialleper

    socialleper Bringer of doom and top shelf beer Supporting Member

    May 31, 2009
    Canyon Country, CA
    Another strange thing that is happening is if I touch the red wire it buzzes more. Same with the bonded black and white cables. Nothing changes if I touch the green.
     
  9. socialleper

    socialleper Bringer of doom and top shelf beer Supporting Member

    May 31, 2009
    Canyon Country, CA
    This set of pickups didn't buzz in this or another bass until I reinstalled them.
     
  10. Killed_by_Death

    Killed_by_Death Snaggletooth Inactive

    In that case, I'd try bypassing all the controls & wire it straight to the jack, and if that stops the noise...
    time to start bypassing individual components of the controls to figure out which one is the culprit

    BTW, before shielding my Rickenbacker 4004, I wired it straight to the jack just for funsies & it was dead quiet & really ballsy.

    After I shielded it & put the controls in, there was a tiny bit of noise. (very tiny)
    4004 models use humbuckers also
     
    Last edited: Nov 5, 2017
  11. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism

    Humbuckers buck 60hz hum. Shielding addresses RF interference. They are two different issues with two different solutions.
     
  12. Killed_by_Death

    Killed_by_Death Snaggletooth Inactive

    Humbuckers are also supposed to stop RF interference, since the noise is induced in both coils in opposing directions.
     
  13. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism

    I'm sorry but this is incorrect. Humbuckers still require shielding. At the theoretical level, both issues stem from 60hz noise but, for our application, they are treated as two different issues with two different solutions.
     
    n1as likes this.
  14. Killed_by_Death

    Killed_by_Death Snaggletooth Inactive

    I can't be incorrect, because I've experienced noise with single coils pickups which humbuckers solved.
    and I'm talking about EMI or RFI

    Here's some reading for you:

    Humbucker - Wikipedia

    "interference is significantly reduced via phase cancellation"

    The phase cancellation works for RFI/EMI as well as 60 cycle hum.
     
    DavC likes this.
  15. socialleper

    socialleper Bringer of doom and top shelf beer Supporting Member

    May 31, 2009
    Canyon Country, CA
    This isn't 60 cycle hum. As I said before, these were quiet in this bass and anothers. The buzz doesn't change if I move around like it would if it was RF. Plus the buzz changes if I touch certain wires or if I roll down the tone.
    This isn't an RF problem.
     
  16. Killed_by_Death

    Killed_by_Death Snaggletooth Inactive

    Of course it is a EMI/RFI problem, it's just constant. If it's not 60 Hz hum, it is RF or EM interference.
    Either way, noise is being induced into the pickups or the controls.
    Have you tried moving the instrument & amp to another location?
    possibly even a different power source


    If the EMI is not 60 Hz this is incorrect.
     
    Last edited: Nov 6, 2017
    DiabolusInMusic likes this.
  17. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism

    If you touch the bridge/strings/metal and the noise stops, the issue is RF interference. If you touch metal/strings/bridge and the noise gets louder it points to a grounding issue. Your humbuckers are working properly because the hum would be constant and would change as you moved the bass around. Just because you weren't getting noise before does not mean they weren't susceptible to it.

    Best of luck with your issue.
     
  18. socialleper

    socialleper Bringer of doom and top shelf beer Supporting Member

    May 31, 2009
    Canyon Country, CA
    Tried two amps in two locations in my house. Different cables as well.
    I haven't had a chance to start that yet.
     
  19. Killed_by_Death

    Killed_by_Death Snaggletooth Inactive

    Were those switches in this bass previously?
    when you had the pickups installed & they were quiet

    It looks like you're only using two terminals on each of those switches.
     
  20. DavC

    DavC

    May 17, 2005
    Tallmadge , Ohio
    try a different grounding scheme

    use the multi meter to check continuity

    i've never had any noise issues , RFI , with properly wired , grounded humbuckers in my 40+ yrs of playing bass/gtr ..
     
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
    May 16, 2022

Share This Page