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single coil wiring - adding a dummy coil

Discussion in 'Pickups & Electronics [BG]' started by Rodent, Jun 21, 2005.

  1. Rodent

    Rodent A Killer Pickup Lineā„¢ Commercial User

    Dec 20, 2004
    Upper Left Corner (Seattle)
    Player-Builder-Founder: Honey Badger Pickups & Regenerate Guitar Works
    I've done some searching this morning and found nothing but 1's and 0's, so I started a new thread hoping that thread 10 on this topic doesn't exist ... (just a bit of a bad joke, eh?)

    I am building a new 5-string J-style bass that will utilize single coil p/u's in both positions. I'd like to utilize a configuration similar to what Alembic does, and have a dummy coil to eliminate the single coil hum. I am not set on my pre-amp configuration (other than it wll be active/passive switchable) or knob/switch quantity at this point.

    Three questions:

    1) What would the wiring diagram look like if I was to do this as a standard passive Jazz bass? How does the dummy coil get added to the circuit layout to provide the hum cancelling ability without adding p/u signal?

    2) Does it seem possible that this installation could be installed from a rear route so as not to add the Alembic styled cover plate on the front side? If I leave 1/4" of wood on the top, will this dummy coil be close enough to the strings to have the proper cancelling effect?

    3) Will I need to utilize a coil for each p/u, or can one dummy coil suffice?

    TAI for your feedback!

  2. luknfur


    Jan 14, 2004

    my guess is the pre alone would filter single coil hum in active phase, not in passive. Never used a dummy coil but to my knowledge they don't need to be anywhere near the strings and can be stuck in the control bay for that matter. They just need to be tied in with the functioning pups. As far as I know, you would only need one. Whether you could run both pups simultaneously I'm not certain for a fact but I know of no reason it would't work if both working pups could be wired so that current flows are opposite from the working pups yet still keeping the working pups in phase.

    As far a wiring diagram - your on your own as it would be a trial and error thing from my perspective.

    Since Bart (for sure) and SD (I think) make them for Rics, they may have a wiring diagram on their sites though I've never looked for them.
  3. A9X


    Dec 27, 2003
    The dummy/HB coil in the Alembics is integrated as part of the preamp design, essentially a third input to the pre that is added out of phase with the main pickups. As the HB coil doesn't pick up any signal except hum/EMI, it doesn't affect the sound. If you add a HB coil passively the added RLC effects from loading the pickup with essentially another pickup in series or parallel will affect the sound relative to the single coil pickup on it's own.

    There are other ways of ensuring no hum, but they usually require custom preamps or you'll lose the active/passive switching ability.

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