Pickup shielding problem

Freddy G

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OK, I give up.....rather than beat my brains out trying to figure this out I'm hoping some of the pickup gurus here can help me out. I've got a Tom Holmes H455 in the bridge position. Everything wired correctly, but there is no extra shielding effect when I touch the strings. The neck p/up does it like it should.
I checked continuity between the bare drain wire and the pickup base....good. Any ideas? @cooljuk
 

Mick51

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Is the bridge grounding okay? Are all the pot backs linked together so they share a common ground?
 

cooljuk

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Well, for sure that's a tough one to comment on, not having it in front of me.

If...
the pickup is otherwise functioning perfectly (sounds right, not thin/weak/muted)
...and...
the pickup is built with 2 conductor braided shield

...then, one end of one coil must be connected to ground/shield/chassis internally, because the braided shield is physically touching the baseplate at the exit, even if it wasn't soldered internally.

I can only imagine one situation where you would not get the expected grounding result: there is a break in a coil that is still capacativly coupled - passing the AC signal generated by the coils but not giving true continuity.

What happens if you test continuity through the pickup from hot to ground using DC?
 

Freddy G

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Is the bridge grounding okay? Are all the pot backs linked together so they share a common ground?
Yes, as I said everything is wired correctly.

Well, for sure that's a tough one to comment on, not having it in front of me.

If...
the pickup is otherwise functioning perfectly (sounds right, not thin/weak/muted)
...and...
the pickup is built with 2 conductor braided shield

...then, one end of one coil must be connected to ground/shield/chassis internally, because the braided shield is physically touching the baseplate at the exit, even if it wasn't soldered internally.

I can only imagine one situation where you would not get the expected grounding result: there is a break in a coil that is still capacativly coupled - passing the AC signal generated by the coils but not giving true continuity.

What happens if you test continuity through the pickup from hot to ground using DC?
Thanks for commenting James.So yes, the pickup is functioning correctly. It's a 4 conductor pickup. No continuity from hot to ground. Each coil measures 4.11k ohm DCR.

So I've been fooling around more and tried swapping the leads ....the red wire was my hot and the black was ground in order for the pickup to be in phase with what's in the neck. So when I made black my hot and red the ground there was an improvement. Now I'm getting the shielding effect, but only subtly. Very strange!
 

DarrellV

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So when I made black my hot and red the ground there was an improvement. Now I'm getting the shielding effect, but only subtly. Very strange!
Looks like there are a black, white, red and green wire .

I'm guessing black and white is one coil and green and red is the other.

Have you tried switching the coil connection wires with one of the ones you are using for signal now?

You are using black and red for signal, so white and green must be spliced together..

Try white for ground and black for interconnect... maybe the coils are OOP internally..

My 2 cents. Please don't laugh too hard, it's the end of a long day.

 

Freddy G

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Well nothing else is making sense so I might as well give that a try.
 

cooljuk

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Do you suppose one of the colored leads is internally shorted to chassis ground / shield? Normally, that connection is only made externally on 4 conductor pickups, once phasing and wiring has been determined, but ya never know...
 

Freddy G

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Do you suppose one of the colored leads is internally shorted to chassis ground / shield? Normally, that connection is only made externally on 4 conductor pickups, once phasing and wiring has been determined, but ya never know...
Yes I checked that before posting this thread. None of the coloured leads have continuity to ground.
 

cooljuk

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Anything happen when you touch the cover or pole screws, while plugged in?

You can try making a new ground with an alligator clip jumper from the baseplate to tailpiece, in case the shield connection of the hookup lead has been compromised.


Probably obvious but if you use coated strings, like Elixirs, the coating acts like electrical insulation.
 

CB91710

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A long shot here... but are the strings installed?

I have a set of Vintage Noiseless in a Tele that were buzzing like a P90 with the gain cranked when I touched the bridge, but were quiet when I wasn't touching it. This was the final build when I was assembling the parts and had not strung it up with anything other than a couple of pieces of monofilament to align the neck.
I fought it for hours... foil tape (which I've never felt the need for), tweaking the bridge ground, checking connections....
I finally gave up and figured I'd just leave the bridge ground off, and strung it up.

Lo and behold, with the strings on there was the normal gentle hum, but when I touched the control plate (Tele, so it was grounded), the noise went to zero.
I lifted the bridge and reconnected the bridge ground and everything was perfect.
Apparently, the strings passing over the pickups have an impact on the noise cancellation?

Could have blown me over with a feather... I've never seen anything like that before.
 

Freddy G

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Anything happen when you touch the cover or pole screws, while plugged in?

You can try making a new ground with an alligator clip jumper from the baseplate to tailpiece, in case the shield connection of the hookup lead has been compromised.


Probably obvious but if you use coated strings, like Elixirs, the coating acts like electrical insulation.
No change when I touch pole screws or slugs (no cover)
Even though I measure continuity from the ground wire (and shielding foil) to the base plate I tried the alligator clip jumper...no difference. Even tried hooking the pickup directly to the output jack bypassing ALL electronics. No difference.
Tried swapping coil connection as per Darrell's suggestion, no difference,
Strings are not coated. Besides I mentioned in my original post that the neck pickup is behaving properly in this regard.




A long shot here... but are the strings installed?

I have a set of Vintage Noiseless in a Tele that were buzzing like a P90 with the gain cranked when I touched the bridge, but were quiet when I wasn't touching it. This was the final build when I was assembling the parts and had not strung it up with anything other than a couple of pieces of monofilament to align the neck.
I fought it for hours... foil tape (which I've never felt the need for), tweaking the bridge ground, checking connections....
I finally gave up and figured I'd just leave the bridge ground off, and strung it up.

Lo and behold, with the strings on there was the normal gentle hum, but when I touched the control plate (Tele, so it was grounded), the noise went to zero.
I lifted the bridge and reconnected the bridge ground and everything was perfect.
Apparently, the strings passing over the pickups have an impact on the noise cancellation?

Could have blown me over with a feather... I've never seen anything like that before.
Yes the strings are installed.

I'm done. I think I have tried everything. My conclusion....something strange with the pickup....which as a professional is a lame conclusion.



Thanks fellas for your suggestions.
 

cooljuk

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Hard to say more without having the instrument in front of me. Some pickup problems are stubborn/sneaky. I start taking them apart at that point, separating them into their pieces, to isolate a problem.

Have you tried crushing it in a hydraulic press and replacing it with a known good pickup? :run:




If you cover the shipping, I'll rebuild it. ....or, even better, just get you something else.
 




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