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Tricks of the trade for testing grounding issues?

Discussion in 'Pickups & Electronics [BG]' started by fnordlyone, Oct 9, 2013.


  1. Quick run down: I am fnord-- exploring newb. I have a J Bass type, 5 string, passive emg blades. The only problem is noise: call it buzzzzhiissss. It goes away when I put a finger on any of the three knobs. Full disclosure: recently threw a wire from the tone pot, learned to solder and fixed it, and some noise went away. I don't want to pull all the guts for a shield job until exhausting all avenues. How do I test if my grounds are grounded? I have ohm meter, but don't know where to put the black and red wires to do any kind of trouble shooting.
    Any advice would be appreciated,
    fnord!
     
  2. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    If your ohm meter is a multimeter then it has a "continuity" test setting, and that's what you use. Touch either one of the probes to the sleeve (outer contact area) of the output jack, then touch the other probe to any other point in there that you want to see if it's grounded.

    Shielding is always a good idea, not to be avoided. :)
     
  3. topo morto

    topo morto

    Mar 22, 2010
    Lloegyr
    So I guess the question is : what bits should be grounded? bridge, strings, backs and shafts of pots, the ground lead to the pickups, the ring contact for the jack... all the shields of course... what else?
     
  4. uOpt

    uOpt

    Jul 21, 2008
    Boston, MA, USA
    If it goes away if you touch knobs or the output plug but not when you touch the strings then your strings are not grounded.

    The way that normal electric guitars/basses work is that they abuse your body as a shield via putting you on mass via the strings and bridge.

    The solution is either to connect the bridge to mass or to do proper shielding inside the guitar/bass.
     
  5. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism Supporting Member

    If the buzz gets louder when you touch metal/strings/bridge you have a grounding issue.

    If the buzz goes away when you touch metal/strings/bridge you have a shielding issue.

    If the buzz remains constant while touching the metal/strings/bridge you have a deeper issue.

    No need for a meter in this situation. You should run a ground wire from under your bridge to the output (or somewhere in the wiring) and be sure to ground the shielding you need to add in the control cavity and both pickup cavities.
     
  6. Thanks for the responses. I took off bridge and the ground wire looks good. Everything's 0 ohms. Since I have the strings off, I'm going to shield pu cavities. Is ok to use Foil Tape? only thing I can find local. It's stated use is for sealing ducts. It's labelled simply Foil Tape; any other options beside copper?

    thanks again,
    fnord!
     
  7. topo morto

    topo morto

    Mar 22, 2010
    Lloegyr
    I just used aluminium kitchen foil and crimped it to one of the ground wires. I believe that is supposed to be a stupid way to do it. Works perfectly though.
     
  8. by crimping to neg. wire do mean: an exposed section of wire?
     
  9. topo morto

    topo morto

    Mar 22, 2010
    Lloegyr
    Yep, IIRC there was a big unshielded wire that went off to the bridge that I could just crimp the foil to (I had heard that you can't solder aluminium, and didn't try to). Shonky job, like I say, but have never heard even the tiniest bit of hum from that bass since.
     
  10. uOpt

    uOpt

    Jul 21, 2008
    Boston, MA, USA
    If the bridge ground was good the hum would get better when you touch the strings.

    The important part to shield isn't the pickup cavities. It's the electronics cavity and the wires leading to the pickups (if they aren't shielded wires in the first place). Don't just glue up the pickup cavities, it can be useless and maybe harmful.
     
  11. Thanks for the advice. No worries, all I tried was to run an extra negative from output to tone pot (where bridge neg was soldered). Buzzhis is still there.
    To be clear: there is no difference when I touch or don't touch the strings... The buzz is constant, unless I put a finger on one of the control knobs. Hell, if the buzzing would stop when I play, I wouldn't be tearing my bass apart. The wires are all shielded (I assume this means insulated with the rubber covering). Was thinking of trying to add negatives that branch all pots, would this be a waste of time? Should I bite the bullet and do a thorough shield job? Will nothing work? Should I just play and try to tune out the noise?

    thanks, once more,
    fnord!
     
  12. uOpt

    uOpt

    Jul 21, 2008
    Boston, MA, USA
    Then your strings are not connected to ground. Unless you have tapewound strings. In a pitch you could use an antistatic wristband but either way you just confirmed that whatever mass the control knobs are connected to is not connected to the strings.
     
  13. I pulled the bridge and the end of the wire was lying smashed under the bridge against the body; should I modify? How, except through the bridge, can I ground the strings?
     
  14. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    alpha-music.com
    maybe scrape some paint off the bottom of the bridge so that squished bit of wire makes a better connection?

    check the other end of that wire; it should be going to ground somewhere, too.

    touching the strings should be exactly like touching the knobs, like uOpt says.
     
  15. uOpt

    uOpt

    Jul 21, 2008
    Boston, MA, USA
    Do you have an ohmmeter?
     
  16. yes. i have an ohmmeter.
     
  17. uOpt

    uOpt

    Jul 21, 2008
    Boston, MA, USA
    So what's keeping you from just making bridge contact and use the ohmmeter to make sure it worked?
     
  18. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism Supporting Member

    In regards to the bridge, I would attempt to reconnect that ground wire. I like to put a strip of copper foil tape under the bridge and push the wire into that, it ensures a good contact.

    In regards to sourcing stuff locally, go to a stained glass supply shop. They will stock copper foil tape, it works much better than the aluminum foil tape they use for ducting. You can also solder to copper foil tape relatively easily, there is an art to solder to aluminum foil tape.
     
  19. Nothing, I've poked the thing all over and get 0 ohms. When you say "make bridge contact...to make sure it works (paraphrase)" What's the technique? I never wanted to be an electrician, but it appears the only option when playing an electric bass!

    all advice appreciated,
    fnord!

    __________________
     
  20. uOpt

    uOpt

    Jul 21, 2008
    Boston, MA, USA
    Do you have contact between the strings and the output plug mass?
     

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