No continuity on individual polepieces

Discussion in 'Pickups & Electronics [BG]' started by ntenny, Nov 10, 2012.


  1. ntenny

    ntenny

    Joined:
    Nov 8, 2012
    Location:
    San Diego, CA, USA
    I've just installed a set of the new Aguilar 4J-HC pickups in a 1973 Jazz. Everything seems to work properly, except for a mild ground hum that I haven't tracked down yet, and one very strange thing that doesn't seem like it could be related to my wiring.

    On each of the two pickups, ONE of the eight polepieces acts as though it isn't grounded; there's a typical buzz when I touch those polepieces. The other polepieces are dead silent. Moreover, breaking out the meter shows continuity to ground on the 14 silent polepieces, but not on the two that buzz if touched. The two affected polepieces are different on the two pickups: #4 of 8 (reading from E to G) on the neck, #5 of 8 on the bridge.

    Is this something about my wiring, or is it the pickups? I can't figure out how I could de-ground an individual polepiece but not the others that share the coil with it.

    The pickups sound good so far, but I'm not going to post a review until I've got them set up right.

    Any ideas, or should I go straight to Aguilar tech support?

    Thanks

    -NT
     
  2. ntenny

    ntenny

    Joined:
    Nov 8, 2012
    Location:
    San Diego, CA, USA
    I've done some investigating. There was a ground short underneath the bridge pickup; fixing that helped a lot with the hum but didn't address the continuity with the polepieces. The ground hum is at a livable level, though I'd still like to get rid of what's left. But the two polepieces still show no continuity to ground and buzz when touched.

    In addition, the bridge pickup is a LOT quieter than the neck. I believe they're wound differently enough that some difference in volume would be believable, but this doesn't sound like it could possibly be the intended balance.

    So I'm stuck at the same question: Are these pickups OK? Is there any way that the ungrounded polepieces can be my fault?

    -NT
     
  3. SGD Lutherie

    SGD Lutherie Banned

    Joined:
    Aug 21, 2008
    Location:
    Bloomfield, NJ
    Disclosures:
    Owner, SGD Music Products
    On a typical Jazz pickup, the poles are not grounded. But the start of the coil is connected to ground. Since the inside wraps of the coil are touching the magnets, any noise you get when touching them is shunted to ground.

    On a split coil humbucker, the second coil cannot have it's start at ground, since it's connected to the finish lead of the first coil. That's why you need the poles grounded.

    It's very tricky to get a good electrical connection to alnico rod magnets. It's typically done with copper foil tape with conductive adhesive. And even then, it doesn't always stick well.

    If you are getting the hum on the E-A string side, which is where you might rest your thumb, you can fix that by reversing the polarity of both pickups. That way the start lead will be connected to ground.

    Obviously you don't want to take the pickups apart, so I'd contact Aguilar.
     
  4. ntenny

    ntenny

    Joined:
    Nov 8, 2012
    Location:
    San Diego, CA, USA
    Thanks; I think after some careful thought I actually understood that. If I've got it right, then, this is just an annoyance with no effects beyond the noise when I touch the affected polepieces---it shouldn't be affecting the signal of the pickup in any other ways?

    Further experimentation (cross-connecting polepieces to one another) reveals that the first (E-A) coil of the neck pickup and the second (D-G) coil of the bridge are ungrounded; I can make the issue go away by connecting them to their grounded partners, so I guess I could fix it with an attractive piece of conductive tape across the middle of each pickup. But I'm not sure I see that it's worth fixing---this isn't something that's going to come up while I'm playing.

    Edit: But wait---if the whole coil, not just one pole, is ungrounded, why does the meter show continuity on the other three poles of that coil? But if the other poles are grounded, why doesn't connecting the "bad" pole to one of the ones on the same coil fix the problem? Am I overthinking this and I should just shut up and play my bass?

    -NT
     
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