phase issue...?

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by spaceboy, Jan 31, 2005.

  1. spaceboy

    spaceboy Member

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    hey there! got a problem with my strat, but i'l cut to the chase and just ask the questions that'll hopefully solve the problem, if anyone would be kind enough to answer.

    so, to reverse phase, do i simply swap the + and - wires from a pickup, thereby grounding the + and taking the - to the pickup selector in my strat? is there any way to test the phase of a pickup other than just hook them up in the guitar and listen for comparative phase? and finally, in a strat, am i right in understanding (i've read people briefly mentioning this but never actually had it explained...) that the middle pickup is reverse-wound... R-something-else... to the other two? and this produces hum-cancelling in positions 2 + 4? now, this RWR-something, is not the same as being a different phase, right? cos two pickups out of phase in parallel would sound VERY thin, nasally, and in most ways conventionally unpleasent, right?

    ... erm, i think that'll do for now, and i'll have to ask some more questions if i get answers to these... thank you anyone who can help!
     
  2. Jim Collins

    Jim Collins Member

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    In general, to reverse the phase of a pickup, you switch the hot and ground wires. However, if the ground wire serves a dual purpose -- as is the case with vintage style humbuckers, and vintage style Tele pickups -- this isn't all you have to do. You have to seperate the coil ground from the ground for the other metal parts of the pickup -- pickup base, baseplate, etc.

    About the only thing you can test, short of putting the pickup in the guitar, is magnetic polarity. If you know the polarity, AND you know the direction of the winding, you'll know the pickup's proper phase. However, knowing the direction of the winding is not always obvious.

    In modern Strats -- but not vintage Strats -- the middle pickup is RWRP (reverse wound, reverse polarity) with respect to the other two pickups. For two coils to be hum cancelling with respect to each other, the coils must be RWRP with respect to each other. This is not the same as being out of phase. Many people refer to a Strat's inbetween positions as the out-of-phase positions, but this is incorrect. All three pickups on a Strat are in phase.
     
  3. spaceboy

    spaceboy Member

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    "If you know the polarity, AND you know the direction of the winding, you'll know the pickup's proper phase"

    so, with that being true, how come this is true?: "the middle pickup is RWRP with respect to the other two pickups [...] This is not the same as being out of phase."

    and, are you familiar with Lace Sensors? they have a green wire, a white wire, AND the metal shielding all going to ground, with an orange "hot" wire going to the pickup selector... do you think these ground wires serve a dual purpose like those vintage pickups, or would i just try and fit all those ground wires onto the pickup switch?

    thanks for bearing with me!
     
  4. Jim Collins

    Jim Collins Member

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    What is it that allows a humbucker pickup to cancel noise? It is the fact that the two coils are RWRP with respect to each other. They are in phase. They are also usually in series, but the two coils can be connected in parallel, and still be in phase, and still cancel noise.

    How many leads does a Lace Sensor have? When Fender first started using Lace Sensor pickups, the pickups only had two leads. The ground lead served a dual purpose.
     
  5. spaceboy

    spaceboy Member

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    ok, but if the polarity and winding direction tell you the phase, why doesn't having opposite polarity and winding direction give you the opposite phase?

    the newer Lace Sensors that I have have 3 leads and a platted metal shield that encompasses them all. a single orange lead goes to the switch, while the green and white wires, along with the shield, all go to ground.

    cheers!
     
  6. Jim Collins

    Jim Collins Member

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    With your right hand, make a fist, but leave the thumb pointing out. Your thumb represents magnetic north, your fingers point in the direction of current flow. Notice that, no matter where or how you move your right hand, the fingers always have the same relationship with the thumb. This right hand rule is a representation of what happens with a pickup. The magnetic field is going to cause the current to flow in one direction. If you have two coils, and connect each coil the way the current wants to flow, they will be in phase with each other, no matter what the magnetic orientation. If you connect one of those coils backwards, or if you were to flip the magnetic field in one of those coils, with out changing the wiring, the two coils would be electrically out of phase with each other.

    For two coils to cancel the noise, their magnetic polarities must be opposing, but they must still be connected in phase, electrically, with each other -- unless you like the out of phase sound.
     
  7. spaceboy

    spaceboy Member

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    ok, i think i see now - cheers Jim!
     

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