Pole Piece Hum: A Grounding Tutorial

Discussion in 'Pickups & Electronics [BG]' started by mech, Jun 19, 2016.


  1. mech

    mech In Memoriam

    Jun 20, 2008
    Meridian, MS, USA
    Several times a week questions are posted about hum being caused by touching exposed pole pieces. Grounding the pole pieces will eliminate this hum. If the pole pieces are exposed on the back of the pickup and if you can solder you can ground them yourself.

    Use conductive adhesive copper foil and put a strip over the poles on the bottom side of the pickups. Burnish it well to ensure good contact with the poles and adhesion to the plastic bobbin. I use a capped Sharpie for burnishing. Solder a ground wire between the pieces of copper foil of sufficient length for mounting the pickup halves. Then you can either solder a jumper wire between the foil and the ground wire on the pickup, as I did, or you can run a separate piece of wire from the foil to the back of the volume pot, or any convenient ground, if the jumper makes you nervous. All soldering must be done quickly with sufficient heat, a clean wet tip and all the other things necessary for a good solder joint.

    The foil is available from several sources. Some more expensive than others.

    This is a P type set for a Peavey Fury I grounded a little while back. This is something I do to any pickup that goes through my hands that has the hum problem. Works for any type pickup where the poles are exposed on the bottom but not grounded. There is a way to ground the pole pieces if they are exposed on the top but not exposed on the bottom. It requires taking the pickup out of the shell and significant handling of the unprotected coil and magnet assembly. If the shell is glued on, removing the shell may cause failure and I don't recommend it. Please don't ask how I know since I'm still PO'ed. PM me if you would like details for pickups with removable shells.

    Grounded%20Poles_zpswgddxrfr.jpg
     
    Last edited: Nov 15, 2016
  2. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism

    Subbed for future linkage.

    Thanks for this boss!
     
    mech likes this.
  3. bassbenj

    bassbenj

    Aug 11, 2009
    Note that this operation is extra important for a P bass with split pickups. The reason is that with a single pickup the coil can be wound with the ground end starting right around the poles and that acts as shield from hum coming in the poles when you touch them. If the hot side of the coil is right at the poles then of course hum is injected right into the bass. But with a split pickup you can't get away with anything because the two halves are in series. And that means that ONE of the two coils is always floating above ground and ready to pick up hum! Grounding the poles puts an end to hum going into the coils from touching the poles.

    Nice piece! I think all poles should be grounded and why makers tend to skimp on this I can't understand.
     
    DiabolusInMusic and mech like this.
  4. mech

    mech In Memoriam

    Jun 20, 2008
    Meridian, MS, USA
    Me either. Maybe it's the "Well, it's always been like that" syndrome. But I won't go there.
     
  5. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician
    Why don't the manufacturers (at least some) not ground their pickup poles? Perhaps because at one time it wasn't an issue. Leo put big chrome covers over his pickups. Not a chance for you to touch the poles. Who would have thought that players would remove the covers? But they did. And it took years for many makers to realize that this created a problem. Many didn't really care - if it was good enough for Fender, it was good enough.
     
  6. swpyne

    swpyne Basses R Loaded! Gold Supporting Member

    Jul 26, 2005
    Centennial, Colorado
    I just followed this process on a set of Nordstrand MP4 P Bass pickups and it absolutely solved the issue. No more buzz when I touch the pole pieces. Bravo to MECH for his insightful and strait forward description. These are the are times I really love TalkBass.
     
    DiabolusInMusic and mech like this.
  7. jastacey

    jastacey

    Feb 8, 2009
    Houston,Tx
    I had an issue with the Bill Lawerance P-46 pickups along with a Audere Classic 4 band preamp, they are encased in epoxy, couldn't get to the poles, went to another pick-up and did ground the pole pieces, and the hum went away .... anyways, here's a link, the the folks at Audere sent me, it really explains the issue
    Audere Audio Pole Piece Noise FAQ
     
    cms likes this.
  8. MdC64

    MdC64

    Jan 25, 2011
    Albuquerque
    Reviving a great tutorial.
    I installed Seymour Duncan Steve Harris SPB-4 pickups in my 2011 American P bass. I’m getting the hum when touching pickup covers.
    The pups come shielded from the factory as well as the ground wire connecting the pups and the small lead connecting the ground to the copper tape.
    Would it be okay to solder another ground wire from the back of the pup to the back of the volume pot? I’d like to try this fix first before any of the below solutions.
    The bass never made noise with the stock pups…strange.
    Solder joints are good…double and triple checked them. I used a multimeter and all is good there.
    I called Seymour yesterday and the tech guy wasn’t much help and he didn’t have knowledge of the SPB-4. Actually because of all the TB searching I knew more than he did so thanks to all of you.
    About 1 1/2 years ago I installed Wilde P-46 pups in my CV 70s p bass and they are dead quiet.
    I’ve spent a good amount of time searching on TB so I know about:
    -shielding the cavities with copper foil although they are lined with conductive paint
    -clear nail polish
    -reversing the wires
    -tape over pole pieces
    -solid pup covers
    -etc…
    I don’t always rest my thumb on pup cover but when I do I’d like it quiet.
    Thanks.
    34A5367C-9618-4F8A-B8E3-E3FECDA1084F.jpeg
     
    Last edited: Mar 30, 2022
  9. dwizum

    dwizum

    Dec 21, 2018
    That pickup wired white as hot and black as ground will be about as silent as it possibly can be. You can certainly run another wire straight from the shielding on the pickup to the volume pot but it'll just be duplicating the wire that's already there. It won't hurt anything if you want to try it.

    My bet would be that good shielding in the cavities will be the most helpful thing for that pickup, since the wiring isn't shielded.

    Another option is to take the cases off the pickups and put narrow strips of copper tape on the top, on either side of the pole pieces, so that the edges of the tape are just touching each pole. That will add more shielding and further ensure that the poles are all well grounded and well connected to each other.
     
    Mikecan likes this.
  10. MdC64

    MdC64

    Jan 25, 2011
    Albuquerque
    Thanks. I appreciate it.
    I was thinking that it would be duplicating what is already there as well. The copper tape sounds great. I’ll get some and get to work. In the meantime I’m going to enjoy the bass. The pickups sound great.
     
    dwizum likes this.
  11. dwizum

    dwizum

    Dec 21, 2018
    The challenge is knowing the mechanism by which you're getting noise in the signal and then doing something about it. Some of that is limited by the construction of the pickup.

    Even pickups with properly grounded poles can sometimes have noise when you touch the poles. Sometimes this can be due to capacitive coupling between the poles and the coil wire. If the coil is wound with the ground end of the coil on the "inside" then this is much less likely. Some coils wound with the hot end of the wire on the inside can be more susceptible to this type of noise, and there's little that can be done about it except insulating the poles (i.e. clear nail polish, tape, or closed covers).

    If shielding or other changes don't work, that's the road you may need to take.
     
    Mikecan likes this.
  12. 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 17, 2022

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