Yet another P-bass hum question

Discussion in 'Pickups & Electronics [BG]' started by Fletz, Jan 22, 2014.


  1. Fletz

    Fletz Supporting Member

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    Hey there -

    I have my beloved 2008 American Standard Precision bass. I took it to my local shop to have "Fender Original Precision Bass" (1962 reissue) pickups installed. The tone is awesome - of course! However, when my fingers touch the poles while playing, I get an ugly "BZZZZZ." They installed the ground plate under the pups. My pickguard has no tape on the back of it. And, the electronics cavity is bare. Would (a) adding shield tape to the pickguard help and (b) shielding the cavity help?

    Is this something I can do as an electronics simpleton? I have changed pickups on other basses, installed a dozen bridges and changed tuners.
     
  2. pfox14

    pfox14

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    Why would your fingers be touching the pole pieces? I don't understand. Anything that comes into contact with the pole pieces is going to make an ugly sound.
     
  3. Fletz

    Fletz Supporting Member

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    Sometimes when I play on the A-string my thumb is on my E string and it contacts the raised pole of the pup.
     
  4. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism Gold Supporting Member

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    Is the noise affected by you touching metal/strings/bridge? If the noise goes away when touching metal, it is a shielding issue. If the noise gets louder, it is a grounding issue. If the noise remains constant, it is a deeper issue, but I would double check the ground wire under the bridge and ensure it is making good contact.
     
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  6. Fletz

    Fletz Supporting Member

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    It only happens when I touch the pole piece. It is dead silent otherwise. When I touch the pole and a string or the bridge or anything it is the same bzzz.
     
  7. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism Gold Supporting Member

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    I have seen the issue before on basses, but they always had shielding issues as well, the issue did go away when I shielded the basses but it could be something else. I am not an electronics wizard, so take my advice with a grain of salt.
     
  8. Fletz

    Fletz Supporting Member

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    And shielding is really most simply putting the copper tape in the cavity?
     
  9. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism Gold Supporting Member

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    Shield the cavity, the pickguard, and the pickup covers and ground all the shielding. Bring the cavity shielding up over the screw holes, at least one, so a screw pierces both sets of foil. On the pickup covers, I bring the copper tape around to the outside so I can solder onto the tape, you can also make really long skirts so the shielding touches the cavity shielding, but I only did that with aluminum tape as it is really hard to solder to. Do not forget to wrap the pickups with electrical tape, you do not want them to touch and shielding. It will be a tight fit.
     
  10. Fletz

    Fletz Supporting Member

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  11. David Jayne

    David Jayne

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    This is not a shielding problem. Reverse the +/-wires from the pickup.
     
  12. Lownote38

    Lownote38

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    I agree. A P-Bass (due to the pick up design) shouldn't buzz at all. I've never had one that did.
     
  13. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism Gold Supporting Member

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    I have had plenty of P basses get 60hz hum.
     
  14. David Jayne

    David Jayne

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    This isn't a hum problem, it's a buzz problem. The poles are closest to the innermost coil wraps and can induce noise. That's why the innermost (start ) part of the coil should go to -. I'll bet it's reversed.
     
  15. Fletz

    Fletz Supporting Member

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    So is it just flipping the pup? Top to bottom?
     
  16. MR PC

    MR PC

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    I've had the same problem with the Original '62. And just about every other standard passive P pickup out there. When you touch the pole pieces, there is a hum, simple as that. My fix has been to use a carefully applied drop of nail polish on the pole pieces. Eliminated the problem every time and is completely reversible.

    I haven't tried reversing the output wires at the pot, that sounds like a good idea.

    Reversing the wires flips the polarity, I've done that with J pickups (both) and eliminated mysterious hum problems. (Sometimes)
     
  17. David Jayne

    David Jayne

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    No, you have to reverse the wires.
     
  18. aphexafx

    aphexafx A mind is a terrible thing. Supporting Member

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    Correct. If the poles are on the hot side of the coil output then touching them will induce buzz. Flipping the polarity of the pickup will ground the poles, if that's actually the issue.
     
  19. David Jayne

    David Jayne

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    It will at least 'inductively ground' them. They probably aren't electrically bonded to the coils.
     
  20. RobbieK

    RobbieK

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    +1^^

    It's best if the inner windings of the coil is the earth side of the coil for pickups with exposed magnets. The problem with P pickups is that the coils are in series, so you can only effectively do this for one coil. The other coil will have its inner windings halfway between hot and ground and will buzz quietly when touched.

    So you have to decide which coil should be quiet and which can buzz a little. If you play with a pick, generally it's best to have the DG coil silent as your little finger will brush the pickup when curled under you palm. If like the OP (and me) you play mostly with your fingers, I've found it best to have the EA coil silent as we often put our thumb on the E and A strings and this often touches the magnets.

    Before you swap coils or wires, you have to touch the DG coil. If it's quiet, then don't swap the wires, swap the coils. If it buzzes even louder than the EA coil, swap the wires, but not the coils.

    You can also earth the bottoms of the magnets. Most modern pickups will be designed with earthed pole pieces. You need to get some copper tape with conductive adhesive, clean the bottoms of the magnets, then put a strip under each bobbin and solder an earth wire to this. Be aware that if you do this with vintage fender pickups there's a good chance you will short it or partially short it because often the inner windings are short to the magnets as there's no insulating tape around the magnets. However, vintage pickups that are like this can work for years and years before needing a rewind if their phase is sorted out.
     

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