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Voltage output per coil in a hybrid humbucker

Discussion in 'Just Pickups' started by Antigua Tele, Jan 3, 2018.

  1. Antigua Tele

    Antigua Tele Friend of Leo's

    Jun 2, 2014
    west coast
    One popular mod DIY guitar modders like to do is create "hybrid" humbuckers, where you take the coils from two different P.A.F. style humbuckers and place them together in a single pickup for a "half-this", "half-that" pickup.

    What is known from a circuit analysis standpoint is that you won't get two strong, different resonant peaks from the two coils, but rather you calculate for the sum of inductance from the two coils, and you get a single inductance and a single prominent resonant peak. So this sort of mod is not quite as exciting as people might thing, because the two coils sort of wash together rather than retain distinct transfer functions.



    Hot coil vs. cool coil

    But I got to wondering, if one coil has a higher inductance than another, will that coil also produce more voltage? If coils were merely inductors, such a question wouldn't apply, but since pickup coils are also a voltage source, this question arises.

    So I did a test where wired the screw coil of a Jazz and the screw coil of a JB together in series (neither slug coil is involved), and excited the coils in the same manner, and compared the output voltage, and it turns out that the JB, with the higher inductance produced quite a bit more voltage than the Jazz coil.

    The inductance of the Jazz by itself is 3.9 henries, the JB 8.0 henries. The inductance of the Jazz screw coil alone is 1.7H, and the inductance of the JB screw coil is 3.5H, about double that of the Jazz screw coil. Inductances in series add together, so 1.7H +3.5H = 5.2 henries, and I get that measured value when I test the two coils in series as well.

    Here are the measurement bode plots, unloaded, and loaded with a standard dummy load:

    no load:
    [​IMG]

    with test load:
    [​IMG]


    It can be seen that 3.4dB boost for the JB, the coil which has about double the inductance when measured by itself.

    Note that the resonant peak is the same, which proves that the inductances of the coil combine to create a single dominant resonance.

    The take away from this is that when you create a hybrid coil, if one coil have a much larger inductance than the other, it will also dominate in terms of signal output, and so the orientation of the hybrid pickup will have a real effect on the harmonic voicing of the pickup. A second take away is that the coils combine to create a new transfer function, they don't port the transfer function over from the pickups they came from.




    Slug coil vs. screw coil

    A side question is, how much different is the slug coil from the screw coil, all other things being approximately equal? The JB's screw and slug coils measure 8.22k for the screw and 8.06k for the slug coil, and the inductance were nearly equal, 3.54H for the screw and 3.52H for the slug coil. So I wired the JB in standard series mode, and measured the output with the exciter over each coil, and the result was that the slug coil produced slightly more voltage:

    no load:
    [​IMG]

    with test load:
    [​IMG]

    It can be seen that the slug coil produces slightly more voltage than the screw coil, even though the screw coil appeared to be ever so slightly hotter. This makes sense, since there is clearly more steel mass near the guitar string / exciter coil with a slug than with a screw, and so there is a greater amplification of flux, or in technical jargon, there is a lower magnetic reluctance between the slug and the magnetomotive force, than there is with the screw.

    Strangely, the plot with the added parallel load showed a greater difference, 0.6dB versus 0.3dB. Usually added load tends to diminish differences, but in either case, the fact that the difference is less that 1dB means you won't likely hear a difference, so these coils can be considered "matched" for all intents and purposes.

    The take away here is that when creating hybrid coils, you don't have to worry too much about whether you're using the screw or the slug coil, because all other things being equal, they will perform about the same.



    Pic:

    [​IMG]
     
    Last edited: Jan 3, 2018
    LowThudd likes this.
  2. LowThudd

    LowThudd Friend of Leo's

    Feb 11, 2014
    Sherman Oaks, Ca
    Cool stuff! I was just wondering about this as the pickups I am planning on switching from ceramic to alnico have no screw poles. I just won't worry about that then. lol
     
  3. Michael A.

    Michael A. Tele-Holic Ad Free Member

    968
    Jan 12, 2013
    Virginia Beach, VA
    Would those be DM K10's, as found on Hondos? If so, please report the results.
     
  4. LowThudd

    LowThudd Friend of Leo's

    Feb 11, 2014
    Sherman Oaks, Ca
    Peavey P-12. "The hottest ceramic pickups Peavey makes" are in my Vortex EXP offset V. They actually don't sound all that bad. But, I was going to change them out but figured I would play with the magnets first.
     
  5. Antigua Tele

    Antigua Tele Friend of Leo's

    Jun 2, 2014
    west coast
    Followup, I've since also found out that in a hybrid humbucker with coils of different inductance, when wired in parallel, the coil with lower inductance will produce higher voltage than the coil with a greater inductance, so that's the opposite of what happens when the hybrid pickup is in parallel. It turns out the reason for this is because the way impedences combine in series versus parallel, in relation to whichever coil the voltage is being induced in.
     
  6. Zepfan

    Zepfan Poster Extraordinaire

    Nov 30, 2013
    Horn Lake, MS
    Seymour Duncan P Rail comes to mind. It does humbucker very well and P90 well enough, but the mini-blade single is just meh.
     
  7. Antigua Tele

    Antigua Tele Friend of Leo's

    Jun 2, 2014
    west coast
    That's a good point, I measured a set http://guitarnuts2.proboards.com/thread/7894/seymour-duncan-rails-analysis-review The L of the P-90 and the rail are 6.2 henries and 4.5 henries, for the bridge pickups, and 5 henries and 2.8 henries for the neck, so they're reasonable far apart. The magnetic coupling between the "rail" and the screws of the P-90 are also different, so that will create a power imbalance too. A regular humbucker with similar bobbins, screws and pole pieces is an almost magnetically homogeneous setup, as can be seen in the first post. But if you set that aside, the rail would be louder in parallel, and quieter in series.
     
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