Pole Piece Hum: A Grounding Tutorial

[mech]

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.

 

[DiabolusInMusic]

Subbed for future linkage.

Thanks for this boss!

 

[bassbenj]

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.

 

[mech]

........I think all poles should be grounded and why makers tend to skimp on this I can't understand.

Me either. Maybe it's the "Well, it's always been like that" syndrome. But I won't go there.

 

[Turnaround]

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.

 

[swpyne]

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.

 

[jastacey]

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

 

[MdC64]

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.

 

[dwizum]

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.

 

[MdC64]

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.

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]

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.

 

[sabre79]

Grounding the pole pieces will eliminate this hum.
View attachment 2512957

RIP Mech.

I have a P/J set (Hot P-bass and Hot Jazz) from Seymour Duncan. The P split coil pickups hummed like a kazoo factory when I touched the pole pieces as I often do when I play. I used several layers of copper tape on the bottom of the pole pieces and sandwiched a wire from each with the copper tape (I figured this would give me a better result then my not so great soldering ability and then I copper taped the wires to the bottom of the copper taped pickup cavity. Problem solved. It's as quiet as my EMG pickups.

 

[Grinderman]

I had to do this for Klein Epic '58 P pickups I have. It was a first for me; I've never had any other P bass pickups that needed this extra work.

 

[Alfonz3]

My P-bass with SPB-3 and tapewounds was humming so I shielded both cavities. But it still had a nasty hum when I touched the poles, especially the E&A side, so I used the "copper tape on the poles with ground leads" trick and now it's totally silent. Brilliant! TB is like the Encyclopedia Britanica of bass.
Big Love and many thanks to Mech (RIP) and others here!

 

[Mark Ambler]

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.

View attachment 2512957

Providing you don’t mind copper coloured pole pieces, run a strip of adhesive copper tape over the pole pieces and ‘wrap around’ at the end of the pickup (under E string), so the tape will run under the pickup foam and make contact with the shielded cavity. Finally eliminated the pole piece noise!

 

[SharpCat]

You can run the copper just on the vertical edge of the pole pieces if you don't want it to show (much). The cover will hold it in place.

 

[Verner]

This was a great thread to run across. If anyone is still looking here, I have a question. Is the only reason we ground pole pieces to eliminate hum when they are touched, or does it contribute to noise reduction in some other way?

 

[SharpCat]

Mostly that. Everything is an antenna, but the frequencies given things pick up are somewhat related to their size relative to the wavelength of the interference. Short little pickup poles aren’t good at picking up audible frequencies without you touching them.

I would expect that grounded poles have some shielding properties for the nearby pickup coil, but that is probably very small.

 

[drewphishesp]

this doesnt affect tone at all right?

 

[SharpCat]

Grounding the poles? No effect.