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G&L MFD humbucker: grounded pole pieces?

Discussion in 'Pickups & Electronics [BG]' started by mozarwasagenius, Apr 1, 2011.

  1. mozarwasagenius

    mozarwasagenius Supporting Member

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    Got me a used L2500

    The pole pieces aren't measuring a low resistance for the pole pieces to ground. Is this normal? I know there is a large copper plate on the bottom of the pickups that the green wire is tied to. Another way to ask the question is, what is the purpose of the copper plate?

    Thanks,
    mozar
  2. Tommorichards

    Tommorichards

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    i think the copper plate is there to "strengthen" the magnetic field, but dont quote me on that.
  3. chadhargis

    chadhargis Jack of all grooves, master of none Supporting Member

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  4. mozarwasagenius

    mozarwasagenius Supporting Member

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    Awesome link! Thanks!
  5. mozarwasagenius

    mozarwasagenius Supporting Member

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    That might make sense.

    I shielded the pole pieces last night and its MUCH MUCH quieter when I touch strings and/or pole pieces - virtually dead quiet.

    I'm using an Audere preamp so don't know how this would apply to the original preamp.

    See these documents:
    http://www.audereaudio.com/FAQ_PUMag_Gnd.htm
    http://www.audereaudio.com/FAQ_PUNoise.htm
  6. 4Mal

    4Mal Supporting Member

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    Did you disconnect the green wire and bypass the copper plate ? Seems to me I recall that being necessary when installing an Audere 3ZB in an L series G&L.

    IIRC Dave has instructions/information about it on his site.
    FWIW - My first Audere experience was with 1 of Dave's demo basses. An early L2K. He brought it to a GTG in Hood River. It was wired up as independant volumes and no tone controls... I spent the next 3 days trying to buy it, unsuccessfully. It sounded amazing.
  7. mozarwasagenius

    mozarwasagenius Supporting Member

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    Yes, I disconnected the green wire. I went a step further and grounded the control cavity and used the springs to ground the copper plate. From the plate I used copper foil to ground the pole pieces. I did this by putting foil tape on the inside of the pickup covers and then using a foil strip grounded to the copper plate to connect to the pickup cover foil... kinda hard to describe.

    Do you have a link to the Audere instructions specific to the L2k???

    The previous owner put an Audere wired for active balance and individual Series/Parallel switches per pickup (its an L2500). It is very nice. Don't think I could live without the balance knob.
  8. RCCollins

    RCCollins Supporting Member

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    isn't the plate there to serve the same (questionable) grounding function as it was on vintage Precisions? Guess we can't ask Leo...
  9. 4Mal

    4Mal Supporting Member

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    Is this a tobacco burst Trib by any chance ?
  10. mozarwasagenius

    mozarwasagenius Supporting Member

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    Nope. Honeyburst USA L2500
  11. bassbenj

    bassbenj

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    I use the G&L circuit in mine. I've added a single coil mod as well as a "global" series/parallel switch. The latter requires that you disconnect the green wire on at least one of the pickups from ground. I use the G&L preamp circuit and have never used the Audere.

    The lack of grounding on the pole pieces is just one more G&L wiring mistake. This means that if you touch the poles it injects hum right into the center of the coils. The answer is to ground the pole pieces. There are a variety of ways to do this. What I did was get a Radio Shack conductive paint pen. There is a copper plate on the bottom of the pickup that is grounded to your shield by springs under the pickup. I used the conductive paint pen to put a stripe along the edge of the copper plate and down onto the edge of each pole piece sort of sticking out under the copper plate. Worked fine. I'm sure you could easily do the same thing with conductive glue copper foil.
  12. mozarwasagenius

    mozarwasagenius Supporting Member

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    I'm finding the coils may need to be shielded (from the side of the pickup)

    Any suggestions on how to do this? I was thinking of doing it inside the pickup cover but being careful with shorting the coils to it (covering with tape beforehand for example)

    Thanks
  13. bassbenj

    bassbenj

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    Probably the best way (the way I did it. :D) is to simply shield the pickup cavity the standard way. (Sides and bottom) The problem with doing this inside the pickup is that the copper foil tends to interact electronically both with the magnetic field (eddy currents) and capacitively to the outside of the coil. So keeping the shield farther away reduces this interference that can change your tone.
  14. mozarwasagenius

    mozarwasagenius Supporting Member

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    I'll give it a try. Thanks for the suggestion


    Do you find a different level of hum in series vs parallel mode. Or (and I hope) you hear no hum/buzz?
  15. SGD Lutherie

    SGD Lutherie Supporting Member

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    Disclosures:
    Owner, SGD Music Products
    It's a steel plate. It's copper plated to stop it from rusting. It does boost the magnetic field.

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