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Success shielding and grounding a vintage P Bass without shielding the pickup cavity

Discussion in 'Basses [BG]' started by Snaxster, Aug 14, 2012.


  1. Snaxster

    Snaxster

    Nov 29, 2008
    Yesterday, I completely eliminated electrical hum and micro-shocks in my vintage Fender Precision Bass. Finally! What may be novel about the treatment is that I did not shield the pickup cavity.

    [DISCLAIMER: In the matter of electronics, I am a beginner, not an expert. This post is merely a testimonial that might be helpful to others. If you try anything I describe here and diminish an instrument in any way, it is not my fault.]

    When two days ago I broke a 3.5 year old string on my vintage P Bass, instead of crying (always an option if you favor old strings, as I do), I said "I'm goin' in!" This was my chance to 1. oil the fingerboard, 2. swap in a darker tone cap, and 3. try to eliminate the electrical hum and micro-shocks I had become complacent about.

    (Since I play bass with double-thumbing/slap/fingerpicking a lot, I can generate enough static to wreak havoc in some basses, especially when humidity is low. This caused a crackling sound in my Nordy vJ4, also fixed, and occasional micro-shocks in my vintage P Bass.)

    After removing the pickguard with the electronics harness, I carefully photo-documented everything. Then I swapped in the tone cap. I then reviewed various instructions for shielding guitars and started applying copper foil tape to the pickguard and electronics cavity.

    Since it was late and I was tired, when that step was done, I considered whether I could get away with not shielding the pickup cavity. I did doubt my ability to correctly set the pickup height on re-installation, so I used that as an excuse to skip the pickup cavity.

    On reviewing my work, I couldn't see how there would be a ground connection to the copper foil. The electronics cavity's foil extended to the body face, so it would connect to the pickguard's foil. And the bridge and pickup each already had its grounding wire connected to the electronics harness. But it seemed to me that nothing connected the foil to ground.

    So I soldered a short length of insulated wire from the ground lug on the jack to the foil on the pickguard.

    I reassembled everything, oiled the fingerboard, re-strung the bass and did a quick setup. Then I plugged in the bass to an amp and... complete success.

    Utterly gone was electrical hum. With the amp turned up loud, the bass volume and tone fully open, and whether my fingers were touching the bass or not, there was no hum.

    Likewise the micro-shocks. All gone.

    My work wasn't the prettiest (and my flash photos make it look worse), but it got the job done. Now my vintage P Bass is completely free of hum and it doesn't sting me when I slap it.

    Best,

    Snaxster
     

    Attached Files:

  2. yup, pretty simple once you understand how to do it... did you shield the pickup's as well? that will take the noise levels down to a further level...
     
  3. João Bourgard

    João Bourgard

    Jan 21, 2010
    Do you need to apply the cooper under the knobs as well?
     
  4. Snaxster

    Snaxster

    Nov 29, 2008
    Hello. Well it may have been old news to everyone else, but it was a revelation to me. I'm always the last to know. :D

    So no, I did not treat the pickups.

    But thank you: it may be that there is still some sort of noise that could be eliminated by shielding the pickup cavity. I was listening with an instrument amp, not a channel strip in a studio; so subtle noise may have been masked by the amp noise.

    Best,

    Snaxster
     
  5. Snaxster

    Snaxster

    Nov 29, 2008
    Hello. Can you see the photos I attached to my original post? If so, study the second one that shows the copper foil applied.

    On my bass, having the copper foil underneath the pots enabled two things: 1. a continuous coverage of the foil on most of the pickguard underside (which I must believe helps), and 2. easy connection of the pickguard's foil to ground.

    Best,

    Snaxster
     
  6. João Bourgard

    João Bourgard

    Jan 21, 2010
    IM kind of afraid to do this to my baby... it as an pre amp circuit and im scared i might mess up
     
  7. bassbully

    bassbully Endorsed by The PHALEX CORN BASS..mmm...corn!

    Sep 7, 2006
    Blimp City USA
    My 84" SQ MIJ Squier started humming allot after I adjusted the pups the other day. It might be a loose wire or something but I think I will do the job like you did once I get under the hood.
     
  8. Snaxster

    Snaxster

    Nov 29, 2008
    "Do or do not... There is no try"... I like your signature, Kyrphen. ;)

    If you have a real doubt, then hire a professional to do the work, I'd say. But if you will do it, I think that half the battle is patience and care: study any instructions you have, both before you begin and as you proceed with the work; before you start any modification, take detailed photos of your bass at each step (so you have a reference if you want to revert and/or for re-assembly); "measure twice, cut once"; etc.

    If you do it and succeed, please let us know.

    Good luck!

    Snaxster
     
  9. Snaxster

    Snaxster

    Nov 29, 2008
    Hello. Sounds good to me. If I were in your position, I would first find the source of the hum related to the pickup adjustment. Then, after fixing that, I would do the shielding and grounding. That way, it's possible to isolate each problem and its fix.

    My two cents!

    Best,

    Snaxster
     
  10. João Bourgard

    João Bourgard

    Jan 21, 2010
    the point here is me doing it like you did so i can learn something... sure i can handle it to a pro.. but then again if I need to have it done again i have to pay up again.

    but yeah I am going to study it and maybe even ask a tech how it's done and document it and post it..

    cheers mate =)
     
  11. Snaxster

    Snaxster

    Nov 29, 2008
    No worries, mate. You and me, both! Right now, I couldn't even afford to hire a lawyer to declare bankruptcy. :rollno:

    And besides, it's about time we learned how to do for ourselves! RIGHT ON!!

    Sorry... I get carried away easily. :D

    Best,

    Snaxster
     
  12. Snaxster

    Snaxster

    Nov 29, 2008
    Okay, tonight I found the practical limit of my fix: when I touch the pickup pole pieces, there is electrical hum.

    Sometimes when I am palm muting, it sounds like rhythmic gated electrical hum, along with the sound of my playing. ;) I've heard this before, ever, but it's more noticeable now that this bass is hum free by default.

    So I plan to follow the recommendations at the Pickup Magnet or Pole Piece Grounding page in the Audere Audio FAQ. While I'm doing that, of course I will shield the pickup cavity, too.

    Step by step...
     
  13. bassbenj

    bassbenj

    Aug 11, 2009

    Obviously you did good! And even though you THINK you didn't shield the pickup cavity you actually did to a degree! I'm talking about the copper foil on the pickguard! Before, the foil was only over the control cavity and now you've put it over a larger area so it goes up and covers the pickups. So that does indeed give you some pickup shielding even though the backside is open (and there is always the hole where the pickups poke through).

    I did the full shield on my Squier PJ and it made a wonderful difference in hum levels.

    For noobs, the electronic ideal for shielding is to enclose all electronics inside a water-tight conductive (copper foil or conductive paint) box that is connected to ground (which means to the body of the bass output jack). Anything outside the box will be an antenna that can pick up hum.

    Obviously you can't reach the ideal of "water-tight" because there has to be a hole where the pickups poke through etc., but the closer you get to the ideal the lower the hum will be. Hence just shielding the control cavity won't be quite as good as shielding both the controls and the pickup cavity.
     
  14. Snaxster

    Snaxster

    Nov 29, 2008
    Well thank you, Sir! That's a good point about the shielded pickguard over part of the pickup cavity.

    I appreciate your encouragement and helpful info.

    When I get around to grounding the pole pieces, I will document the procedure and add it to this thread.

    Best,

    Snaxster

     
  15. New new link for this in 2017 is: Audere Audio Pole Piece Noise FAQ
     
    Snaxster likes this.

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