Can you guestimate relative pickup output of *installed* pickups?

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by Crowder, Feb 28, 2015.

  1. Crowder

    Crowder Dang Twangler Silver Supporting Member

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    I just installed a brand new set of Stew-Mac "Golden Age" humbuckers in my Sheraton. The neck sounds great! The bridge sounds very thin and relatively weak.

    Since they're 4-conductor pickups, and since other pickups in the same guitar have been fine, my theory is that the bridge pickup is only using one coil. However, the red/white leads come soldered together from the factory, and I've checked the integrity of that connection.

    I'm assuming maybe there's a lead loose inside the pickup, maybe. I know I could measure the resistance at the hot and ground leads with the pickup out of the guitar. Is there any way to make the same measurement without taking it apart? Maybe at the jack?

    The electronics are LP/335 style, vintage wiring.
     
  2. Ronsonic

    Ronsonic Member

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    You can measure DC resistance at the jack. Flip the switch to the pickup you're testing and turn the volume all the way up. It won't be precise, but close enough for diagnostics.
     
  3. walterw

    walterw Gold Supporting Member

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    yep, just plug in a cable and measure across tip and sleeve at the other end.
     
  4. FallsRockShop

    FallsRockShop Member

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    You won't get an accurate number without desoldering the pickup leads and measuring them separately. If you measure the value between the jack leads you will be also capturing the ohm value of the pots.

    The value on your meter would actually read out the combined resistance of everything currently wired up in parallel. If you knew the exact values of the pots, which you don't because they're typically +/- 10% for CTS and higher for import, you could deduce the ballpark value of the pickups.
     
  5. Crowder

    Crowder Dang Twangler Silver Supporting Member

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    Thanks guys. I think it will be close enough to tell me if both coils are working.
     
  6. K-Line

    K-Line Gold Supporting Member

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    I keep a jack end around to do such a thing.
     
  7. swiveltung

    swiveltung Member

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    The resistance of a pot wide open should be zero right?. They aren't always but not that far off from zero.
     
  8. walterw

    walterw Gold Supporting Member

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    you end up with a slightly lower number with the pickup wired in, since it's in parallel with the pot;

    like an 8.5kΩ humbucker might read 8.2kΩ or something, plenty close enough to tell you what's what.

    just remember, none of this tells you "pickup output" unless you're comparing two otherwise absolutely identical pickups, in which case the one with the higher DC resistance has more wire wrapped on it and thus is louder and darker.
     
  9. Ronsonic

    Ronsonic Member

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    Measuring DCR at the jack is a perfectly reasonable diagnostic step. Let's do some typical numbers for example: Humbucking pickup - 8.5K; Volume Pot - 500K; Actual reading would be 8,358 Ohms

    That is certainly close enough to know if the pickup is not shorted, open, wired in parallel, etc. The tricky one is if you've got the phasing wrong. That will enfeeble your pickup and still ohm out correctly.
     
  10. lendryesky

    lendryesky Supporting Member

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    Does the bridge pickup hum when it's selected. If it does, then only one coil is being used. Contrast it to the neck pickup.
     
  11. Zexcoil

    Zexcoil Gold Supporting Member Vendor

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    StewMac lists the GA bridge HB at 9 k Ohms.

    If you measure something more like 4 k Ohms at the jack then you've only got one coil.
     
  12. Ronsonic

    Ronsonic Member

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    I keep a tuning fork handy for testing coils. Yeah, you can just tap on them, but remember that wiring error I was talking about earlier. If you put a tine of the fork between the poles you'll hear whether it is reinforcing or cancelling.
     
  13. walterw

    walterw Gold Supporting Member

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    aha!

    what works for me is the tuning fork and my turbo tuner:

    the tuner is an analog strobe, and it represents a pitch with a half-circle display of lights; if i have one coil out of polarity with another, holding the fork over each will produce the half-circle flipped to opposite sides of the display.

    you can do this trick with regular mechanical strobes or even the peterson virtual strobe stuff, but it's a little less obvious: the display has rows of alternating bars and gaps, and when the polarity is flipped the bars switch places with the gaps.

    with all these tests, the key is to hold the fork so that it's parallel to the face of the guitar but "edgeways", with one tine towards the strings and one away, lined up fully over one coil at a time.

    magnetic pickups only sense metal moving towards and away from them, not side-to-side over them.
     
  14. jcs

    jcs Member

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    Have you played around with pickup height?
     
  15. Crowder

    Crowder Dang Twangler Silver Supporting Member

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    OP here. Thanks for the help. Measuring across a cable end worked perfectly. 8.35 or so for the bridge, 7.6 or so for the neck. I had the pickup wired in correctly, and it's not defective. The little amp I was using to test just didn't flatter the bridge pickup at all. I've tested it with two other amps since then and it really sounds nice.
     
  16. Ronsonic

    Ronsonic Member

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    Cool strobe trick.
     

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