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Coil capacitance and tapped coils

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  • Coil capacitance and tapped coils

    Hi again, I'd like to share with pickup makers something interesting I found while analyzing some "coil tapped" Strat pickups. All of those details are here Seymour Duncan SSL-4, Analysis and Review | Fender Stratocaster Guitar Forum

    The finding that I think pickup makers might be interested in is it appeared to me that, when a tappable pickup is coil tapped, there is a significant amount of capacitive coupling between the active inner coil, and the inactive outer coil. This is because when a coil is tapped, usually the outer portion of the coil is still physically touching the rest of the circuit at that tap point, though it's not inducing a current, as it's not connected at one end, but it's still able to capacitively couple with the inner portion of the coil, just as a grounded cover or base plate would, but to the extreme in this case, due to the point blank proximity between the active inner coil and inactive outer coil.

    The take away is that if you want to construct a tapped coil, and get the inner coil to sound more like an underwound coil, try fully disconnecting the outer coil so that it can't capacitively couple. This can be done with a DPDT push/pull, since only one half is required to tap the pickup, the other half of the DPDT can be used to also disconnect the outer coil at tap point. It would also require four conductor cable, and have both halves of the coil connected with their own positive and negative lead wires, similar to a four conductor humbucker scenario, but the potential payoff is a superior tapped tone.

  • #2
    Originally posted by Antigua View Post
    Hi again, I'd like to share with pickup makers something interesting I found while analyzing some "coil tapped" Strat pickups. All of those details are here Seymour Duncan SSL-4, Analysis and Review | Fender Stratocaster Guitar Forum

    The finding that I think pickup makers might be interested in is it appeared to me that, when a tappable pickup is coil tapped, there is a significant amount of capacitive coupling between the active inner coil, and the inactive outer coil. This is because when a coil is tapped, usually the outer portion of the coil is still physically touching the rest of the circuit at that tap point, though it's not inducing a current, as it's not connected at one end, but it's still able to capacitively couple with the inner portion of the coil, just as a grounded cover or base plate would, but to the extreme in this case, due to the point blank proximity between the active inner coil and inactive outer coil.

    The take away is that if you want to construct a tapped coil, and get the inner coil to sound more like an underwound coil, try fully disconnecting the outer coil so that it can't capacitively couple. This can be done with a DPDT push/pull, since only one half is required to tap the pickup, the other half of the DPDT can be used to also disconnect the outer coil at tap point. It would also require four conductor cable, and have both halves of the coil connected with their own positive and negative lead wires, similar to a four conductor humbucker scenario, but the potential payoff is a superior tapped tone.
    That is very interesting. Thanks for pointing that out, and I will take a look at the link.

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    • #3
      On the topic of coil capacitance.. I did a survey of numerous Telecaster neck pickups and found that they tend to have much higher capacitance Measured Electrical Values of Various Telecaster Pickups | Telecaster Guitar Forum

      A typical Strat pickup usually shows 90pF to 140pF. A single PAF style bobbin is usually well under 100pF, but for some reason many Tele neck pickups show a capacitance that his higher than 200pF.

      Does anyone know why this might be? Higher wind tension? Thinner insulation build?

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      • #4
        Originally posted by Antigua View Post
        On the topic of coil capacitance.. I did a survey of numerous Telecaster neck pickups and found that they tend to have much higher capacitance Measured Electrical Values of Various Telecaster Pickups | Telecaster Guitar Forum

        A typical Strat pickup usually shows 90pF to 140pF. A single PAF style bobbin is usually well under 100pF, but for some reason many Tele neck pickups show a capacitance that his higher than 200pF.

        Does anyone know why this might be? Higher wind tension? Thinner insulation build?
        Tele neck p'ups are traditionally wound with Heavy Formvar AWG#43 wire and a Strat neck p'up can be SPN, PE and/or Heavy/light Formvar AWG#42 wire. That might give you a hint.
        Pepe aka Lt. Kojak
        Milano, Italy

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