Noisy Polepieces

[King Tut]

[url="http://basschat.co.uk/index.php?showtopic=33334"]http://basschat.co.uk/index.php?showtopic=33334[/url]

OK -so the refret is done, the trussrod issues are sorted and the cosmetic magic has been applied.

When I touch the polepieces, the bass buzzes badly. I've checked the earth continuity and it's all fine, however I also noticed that the two outside polepieces on the bridge pickup also seem to be connected to earth - one at either end of the pickup - and just on the bridge pickup. Anyone got any ideas what's going on here and a possible solution?

Cheers in advance,

Col

[octavedoctor]

[quote name='King Tut' post='364321' date='Dec 27 2008, 05:49 PM'][url="http://basschat.co.uk/index.php?showtopic=33334"]http://basschat.co.uk/index.php?showtopic=33334[/url]

OK -so the refret is done, the trussrod issues are sorted and the cosmetic magic has been applied.

When I touch the polepieces, the bass buzzes badly. I've checked the earth continuity and it's all fine, however I also noticed that the two outside polepieces on the bridge pickup also seem to be connected to earth - one at either end of the pickup - and just on the bridge pickup. Anyone got any ideas what's going on here and a possible solution?

Cheers in advance,

Col[/quote]

This is not really a fault but is caused by inductive coupling between the signal path and the pole pieces.

Each coil has an "open" side and a "blind" side. The blind side of the coil has the windings running very close to the pole pieces and in vintage style pickups are separated only by a thin wall of (usually) paper tape. The open side comes from the outer coils and the earth path and signal path can be connected to either.

From the viewpoint of noise reduction however, taking the signal wire from the blind side of the coil is very much better as the outer coils become part of the earth path and therefore help to screen the inner windings against inductive noise. Also, if screening foil is fitted, the capacitance effect of this is non existent if the signal path is connected to the blind side.

In a J bass with a noise cancelling pair of pickups one pickup should be reverse wound/reverse polarity however few pickups other than custom designed and calibrated sets are genuinely reverse wound these days and if it's a genuine '76 your pickups are probably wound with the same rotation but different magnetic polarities. In order to achieve noise cancellation with these, one coil will have the signal path emerging from the blind side and one from the open side. The former of these will experience noise when the pole pieces are touched but should have an attenuated high frequency inductive buzz response when in circuit on its own.

You should find that all the pole pieces buzz if you touch them. but if this isn't happening then it could simply be that because the coils are bound to the core more tightly at the bobbin ends on a long J pickup this is just pushing the coupling over the threshold at these points.

Either way, unless you routinely rest your fingers on the pole pieces while playing it shouldn't be a problem and is really nothing to worry about.

Does that make sense?

Eltham

[King Tut]

Thanks Eltham.....errmmm it was a bit technical!

Unfortunately, I do touch the polepieces a lot and the noise is very intrusive. I'd like to keep these pickups in (which are allegedly 77 pups although not the originals) - they sound awesome - is there an easy rewiring fix that would help?

Cheers

Col

[Mr. Foxen]

Eelctrical tape over the poles is a minor mod I've seen fairly often.

[Protium]

Several layers of clear nail varnish should sort it.

[King Tut]

Very simple but practical fixes - silly how the blatantly obvious sometimes eludes us!!

Cheers guys!

Col