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Grounding riddle for the pros

Discussion in 'Pickups & Electronics [BG]' started by pault138, Jan 3, 2012.

  1. pault138


    Jan 3, 2012
    I just asked this on strat-talk as well...


    Hi guys, I'm new here. signed up to ask this question...searched "grounding" and not much came back up.


    The problem:

    This regards two separate guitars. One is a partscaster i put together. This was my first project, and naturally with a weak soldering job. The more recent project is a P bass i put together, this time with better soldering job! (with the help of alligator clips, clean solder tip, flux. etc.)

    A typical grounding issue i think, when i touch the metal components of the guitar, pot shafts, the bridge, the strings, etc. , the hum from the amp goes away.

    This happens for both of the guitars that I wired. I didn't have this problem with my other bass (wired by the pros in the wonderful nation of Korea), which has an onboard preamp & eq, which i mighta read somewhere those have a different mechanism for dealing with ground noise. Also, it doesn't occur with my acoustic that has onboard electrics.. it has the under-the-bridge pickup/mic blend type of things...

    When I leave the amp on, without any guitars plugged in, there is similar hum, but not as loud. Perhaps this is normal...some hum is expected in a turned-on amp that doesn't have a guitar plugged in. (right??? but in this wonderful youtube bit, the wise man says otherwise...from what i'm understanding from his video is that you shouldn't really get much hum even without a guitar. Noise Reduction Pt. 2 - YouTube)

    Some background info:

    i don't think it's simply a single pickup hum issue...positions 2 and 4 are indeed quieter, but in any positions, when i touch the strings, the hum goes away.

    I am not sure if my apt is well grounded! i looked for a ground checker at the local store, but they didn't have em. so I am not sure if it's the apartment problem or a guitar-internal problem. But i did try different wall jacks in my apt, and they all lead to the same results.

    Another interesting thing related to wall jacks; the hum gets worse when i plug in my laptop, through an extension cord, simultaneously with the amp on the same wall jack. The laptop plug does not have a ground lug. But perhaps this is a separate issue that just adds on top of the hum in question.

    On my P bass, I checked each ends of the cold wires within the wiring with a pretty good multimeter. I used the continuity mode of the multimeter to check the connections of each cold wire. They seem ok. But perhaps I should measure the resistence of each segments? I would think the continuity mode would be enough...

    Could cheap wire be a problem? I used the ones from Home Depot, 22 gauge, (or maybe 20) insulated but not shieded.

    Lastly, i'm pretty sure it's not an error in the wiring scheme...followed the diagrams to the word.

    Wiring guitars is pretty fun. the first project was sorta crazy, but the second one i enjoyed. i found the soldering relaxing haha. And as a poor college student, it sure beats actually having to buy the real thing!

    Anyhow, thanks for reading, and any input will be appreciated.
  2. SGD Lutherie

    SGD Lutherie Inactive Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    It sounds like you have poor grounds in your apartment.
  3. fenderphil


    Sep 1, 2006
    Houston, TX
    make sure the wiring to the output jack is correct.

    I rewired a bass the other day that someone had replaced the output jack previously and they wired it backwards.

    it sounds much better now, lol
  4. guy n. cognito

    guy n. cognito Secret Agent Member Supporting Member

    Dec 28, 2005
    Nashville, TN
    Actually, it never means that. If the hum disappears when metal is touched, then it shows that the ground is working.

    This problem can typically be cured by proper shielding. Shield all cavities, making sure to create a complete shield wherever possible. Connect all shielded cavities to the common ground, and it should greatly reduce the problem.
  5. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    yep, it's shielding, not grounding, that is the issue. if it goes away when you touch the strings, it means the strings are grounded.

    korean imports typically have that black paint in the control cavity; it's actually graphite shielding paint.
  6. pault138


    Jan 3, 2012
    Thanks for all the replies guys.

    Yeah I ended up shielding the pickup chamber and the noise reduced significantly....somewhat still there tho...probably because I didn't completely shield it...

    i just had to make do with foil, but didn't bother to completely cover the chamber walls. Anyhow, it sure did help.

    I'm guessing if I used shielded wires for the long runs, etc it'd help more....

    Thanks dudes!!
  7. pault138


    Jan 3, 2012
    and yes, can't be disregarded...I'll try and find a ground checker one of these days, and actually test the ground in the apt.

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