how to reverse polarity in a strat pickup?

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by pacoros, Dec 17, 2009.


  1. pacoros

    pacoros Member

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    i read something about use magnet to reverse polarity but..
    has someone done it?
    what do i need? how dificult is it? can i broke the pickup by accident?
    how it shold be done?

    thanks in advance
     
  2. levelfrets

    levelfrets Member

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    Is the bobbin plastic? If it is which the majority of Fender strat pickups are these days, you can easily push the magnets out and flip them. Otherwise you will need to use a rare earth magnet to reverse the polarity.
     
  3. Rock Johnson

    Rock Johnson Member

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    Or you can just switch the hot and ground wires.
     
  4. from atlantis

    from atlantis Member

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    what would be the reason to reverse the polarity? what does that do for your tone?
     
  5. ScottB

    ScottB Gold Supporting Member

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    That will change the phase, but not the polarity.
     
  6. Eagle1

    Eagle1 Member

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    Forget it as as you need to turn everything around. REVERSE WRAP @ REVERSE POLARITY.
     
  7. walterw

    walterw Gold Supporting Member

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    ok, we're tossing out technical terms interchangeably here.

    reversing the leads will indeed change the polarity of the output signal, just like reversing the magnets would.

    "phase" is something else entirely, even though it always gets used incorrectly to describe this.

    the only drawback to reversing the leads is that now the magnets will be right against the hot end of the coil rather than the ground end, and will make noise when touched.

    if the OP is trying for a RWRP hum-canceling setup with this pickup's neighbor, then yes, the magnets have to be opposite magnetic polarity from the other pickup.
     
  8. ScottB

    ScottB Gold Supporting Member

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    Hmmm,

    You've got a point there. I always just accepted the jargon and never thought about the "technical correctness".

    But yes, since what we are doing with changing (effective) winding direction (or really electron travel direction - as this will allow you to differentiate between a situation where you have swapped the leads and a situation where the coil is physically wound in the opposite direction) and reversing the magnetic field is not really changing phase per se as there is no time domain shift introduced into the signal. We are really just flipping the polarity of the electrical signal which effectively "looks" (at least from a snapshot perspective) like putting the signal 180 degrees out of phase and also "acts" like it from a destructive interference point of view.
     
  9. walterw

    walterw Gold Supporting Member

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    i always have to consciously stop myself from using the word "phase" when i'm referring to pickup polarity.
     
  10. brad347

    brad347 Member

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    I don't want to come across as pedantic here, but it really would be a great idea to do some reading on the difference between polarity and phase.

    People think of sound by visualizing a single sine wave at a single frequency and imagining how that behaves, but anything other than a tone generator does not produce sound that looks like that.

    Phase is something that exists in the time domain. You cannot alter phase by flipping magnets over or reversing wires. Phase is never binary. Polarity is always binary. If you are selecting between two choices, you're dealing with polarity. If you're talking about a difference in time or distance (which for sound purposes IS time), then you're talking about phase.

    If a signal has an 80 Hz component and a 120 Hz component, there is no such thing as "180 degrees out of phase." If you delay the 120 Hz component by one half cycle, the 80 Hz component is delayed by less than that. If you delay the 80 Hz component by one half cycle, the 120 Hz component is delayed by more than that. There are no two ways about it. You could never get total cancellation by shifting phase of a complex musical signal-- you could only get comb filtering.

    However, you could add a signal of opposite electrical polarity and achieve total cancellation. Phase and polarity can interact. A polarity reversal can change which frequencies of two similar out-of-phase signals get comb-filtered. But that's about as far as their relationship goes.

    Recommended reading:

    http://www.digitalprosound.com/Htm/TechStuff/2000/Nov/SquareOne1.htm
     
  11. ScottB

    ScottB Gold Supporting Member

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    Point taken. I should have said "like putting a sine wave 180 degrees out of phase" or "like putting the entire signal 180 degrees out of phase".

    It is easier to visualize this kind of thing by picturing a single frequency but that is a gross oversimplification.

    Practically it is difficult to achieve a signal to be 180 degrees out of phase over the entire frequency spectrum, but theoretically it is easy to visualize. A comb filter can't achieve this, since it incorporates a fixed time delay, and as you have pointed out results in a phase shift that varies with frequency. A fixed time delay is not degrees out of phase, it is seconds out of phase. 180 degrees out of phase over the entire spectrum implies that the time delay is frequency dependent.
     
    Last edited: Dec 19, 2009
  12. pacoros

    pacoros Member

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    i read the stewmac method with 2 magnets. does anyone try it? does it works? does it can harm the pickup?
    thanks
     
  13. levelfrets

    levelfrets Member

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    You would have to reverse the polarity too. You can't just reverse the leads or the pickup will be out of phase with the others assuming this is the middle pickup and it is currently NOT RWRP.
     

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