Pickup wiring...help me understand

Discussion in 'Pickups' started by Tommymc, Sep 22, 2017.

  1. Tommymc

    Tommymc Junior Member

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    I've been installing a Gibson 500T pickup in my bandmate's Les Paul Studio. It's going in the bridge position. The old pickup (and the neck pickup) are Guild XR-7's. He has a habit of anchoring his pinky on the edge of the pickup, and apparently damaged the winding on one of the coils. The 500T installation went smoothly and the wiring is pretty straight-forward.

    My question is about how the Guild pickups were wired. Whoever did the installation, snipped the 4-wire pigtail and connected to the original 2-wire cable n the pickup cavity. The tied the two positive leads together but only connected one negative lead to ground. The other is just snipped and not connected to anything. Both pickups were wired this way, so it's intentional. When you tap on the pole screws, one coil is hot, the other is much quieter. I'm trying to figure if this wiring configuration is simply a split coil or whether the disconnected (-) wire does something different. I'm thinking it might be to add windings for a P-90 sound.
    I didn't test for north-south, but the Guild wiring is
    [Coil 1] White (+)
    Green (-)
    [Coil 2] Red (+)
    Black (-)
    Right now it's wired:
    red & white → (+) to controls
    green → (-) to ground
    black → (-) disconnected.

    The pickup does sound sweet and quite crisp for a neck pickup. The 500T wired in series was a bit too much of a contrast. I ended up wiring it in parallel for a more balanced sound. I'm trying to talk the owner into letting me install a pull up pot switch so he can have it both ways...

    Anyway, I'd appreciate if anybody could enlighten me as to the logic behind the way the old pickups were wired in.
     
  2. DarrellV

    DarrellV Almost 1 Year old this month! Premium Member

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    What you described sounds like the old pickups were indeed running as single coils.
    Normally those two wires should be hooked together as they connect the 2 coils of the pickup to each other.
    In a normal 2 wire pickup they are connected internally.

    Tapping the pole screws shows which coil was live and which was dead. That's why it sounded lighter than the new full humbucker you put into the neck.

    A push pull is an excellent idea if that's the sound he likes.
     
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  3. Al Walker

    Al Walker Senior Member

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    What he said.
     
  4. Tommymc

    Tommymc Junior Member

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    I figured single coil, but is there a reason the hot wire from the unused coil is connected to the live coil? I would have expected the unused coil to either have both leads grounded, or just left disconnected.
     
  5. DarrellV

    DarrellV Almost 1 Year old this month! Premium Member

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    Again your assumptions are correct. That is the best way.

    That part is going to remain a mystery at this point. It is not the ideal way to coil split, but it does work.

    Only one lead needs to be removed to kill a coil, but leaving one hooked up to the active coil is like hooking an antenna into your signal path. Picture hooking a very long strand of wire to your pickup coil and leaving the other end open...

    This is not normally considered the ideal way to do the job, but whoever did it may not have been sure of themselves or electric theory as it pertains to an electric guitar.

    In a high voltage household switch, for instance, one only needs to break one side of the circuit for the light to go out. Job done.

    However, noise is not considered a problem in household wiring. In guitar electronics it is a BIG concern. Lifting only one wire without any grounding is a big NO NO.

    Maybe the guy who did the mod liked to play along with the radio station he started picking up after the mod and though he was on to the next big thing in portable practice devices....
     
  6. Tommymc

    Tommymc Junior Member

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    LOL. Yeah, you're right, the guy probably was thinking like an electrician. I think my bandmate is going to be surprised to find that his humbuckers were only running on one coil. Assuming he wants to keep the neck pickup split, I guess it would make sense to disconnect both leads from the other coil just to cut down on potential noise.
     
  7. DarrellV

    DarrellV Almost 1 Year old this month! Premium Member

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    Yup, you wouldn't even have to ground them, but it wouldn't hurt to do so.

    You know if that's the sound he likes there is always this.... it would be a more elegant solution.
    [​IMG]
     
  8. Dilver

    Dilver Senior Member

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    The Gibson 500T is a crazy pickup. Its ceramic, so it's not about vintage tones; more suited for heavy rock and metal. It will rip your head off with the right amp. A bit of a one trick pony, but man what a trick.
     

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