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FDP Forum / The 'Pup' Tent / Why do some pickup combinations require flipping hot and ground?

littleuch
Contributing Member
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Ocala, Florida

Blowing bubbles
Mar 21st, 2019 09:41 AM   Edit   Profile  

I must have been a wee little lad the first time I encountered the out of phase thing that required switching ground and hot to make a new pickup play nice with another, but never really pondered the reason why. I got time now. Someone please explain.

Yesterday I swapped the existing bridge pickup (GFS Lil Puncher) in my Warmoth Tele to a Bill Lawrence Wilde noiseless. I had that one at another time in a different Tele matched with the Wilde neck pickup with no oddities in wiring. The neck pickup in the Warmoth is a Kent Armstrong Stealth 90 and is wired hot to switch ground to back of pot. Seems to me I should have been able to successfully wire the Wilde in as usual (white to switch, and in this case) black/blue to ground. The middle position was out of phase. Rewired black to switch and white/blue to ground and presto.

I'm sure it's a simple explanation, but...

DrKev

Paris, France

It's just a guitar, not rocket science.
Mar 21st, 2019 10:26 AM   Edit   Profile  

If every manufacturer used the same color coding and magnet polarity it would all be so simple. But they don't and some of them even changed mid-production (like Fender strat single coils changing polarity in '58/'59) on just some of their models. DiMarzio's noiseless single coils use a four conductor wiring identical their full size humbuckers, but magnetically reversed. So if you use noiseless single with a humbucker you have to switch hot and ground on something for everything to work right.

Peegoo
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Just beyond Mars

there's a world of fools
Mar 21st, 2019 10:40 AM   Edit   Profile  

Because guitar pickups are AC voltage generators; they create alternating current.

When both pickups are generating forward voltage at a given frequency, e.g., 440 Hz--an A note--they support one another. But if they are out of phase (one generating forward voltage while the other generates reverse voltage), there tends to be significant portions of the audio signal that are electrically canceled (silenced).

Look here

Achase4u
Contributing Member
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U.S. - Virginia

Mar 21st, 2019 11:13 AM   Edit   Profile  

Yea, it's a free for all with polarity and electron direction.

It's a lot like flipping your phase in pro tools on two microphones on the same source. If they are in phase for the most part, they are additive. If they go out of phase, they cancel each other out.

In your computer you can perfectly cancel out two identical signals to zero. Because pickups are slightly different and sense different parts of the strings they don't ever cancel absolutely, but will cancel a great deal.

Peegoo
Contributing Member
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Just beyond Mars

there's a world of fools
Mar 21st, 2019 11:38 AM   Edit   Profile  

One of the classic ways to mic a snare drum is one mic on the batter (top) head and one mic on the resonant/snare (bottom) head. You have to flip the phase on one of the mics or you'll get phase cancellation because when you thwack the drum, the top head moves away from the upper mic, and the bottom head moves toward the lower mic.

With speakers, having a stereo pair out of phase with one another will cancel out much of the wavelengths equal in length to the distance between the speakers--as well as partially cancel harmonics whose nodes are equal to that distance.

Similarly, in open-back speaker cabs and combo amps, you get phase cancellation at frequency wavelengths equal to the various distances between the front and back of the speaker's cone.

If you want to see a great visual example of constructive (increased wave amplitude) and destructive (decreased wave amplitude/cancellation) phase relationships, look here @4:15 in the vid...

but watch the entire thing because it is *fascinating*

(This message was last edited by Peegoo at 10:31 PM, Mar 21st, 2019)

littleuch
Contributing Member
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Ocala, Florida

Blowing bubbles
Mar 21st, 2019 01:10 PM   Edit   Profile  

So in the world of pickups, there is no real way to determine this particular issue without trial and error?

Peegoo
Contributing Member
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Just beyond Mars

there's a world of fools
Mar 21st, 2019 08:36 PM   Edit   Profile  

If the polarity is unknown going in--yes.

However, many makers have standardized their own color codes, so you'll know how to hook them up with each other or with units from other makers.

Here's a list of humbucker brands I've put together for my own reference.

HB pickup makers' color codes

Te 52

Laws of Physics

strictly enforced
Mar 21st, 2019 10:09 PM   Edit   Profile  

"...So in the world of pickups, there is no real way to determine this particular issue without trial and error?..."

Yes, there is also a way to check the absolute phase of a pickup, albeit a rather involved, nerdy, and time-consuming way. It works best with an analog (needle-type) multimeter, but a digital will do.

Set the multimeter to measure ohms. Attach the pickup + lead to the multimeter + (red) input, the pickup - lead to the - or Common (black) input. Adjust the scale so the needle is somewhere near the midrange of its travel. Now hold a large piece of iron or non-stainless steel -- a wrench will do -- very near the pole pieces and then suddenly move it away, watching the meter while you do so. As the ferrous mass rapidly moves away from the pickup, the needle will quickly swing either to the left or to the right, then drop back to where it started. The direction the needle moves characterizes the phase of that particular pickup. You'll want to do the test two or three times to make sure you're getting a consistent reading.

If you then make the same measurement on a second pickup and the needle moves in the same direction, the pickups are in phase. If the needle swings in the opposite direction for the second pickup, it is out of phase with the first pickup, and one of the two pickups will need to have its leads reversed when it is wired into the guitar.

If you must use a digital meter, set it to volts rather than ohms. The readout should start at zero, then momentarily go either positive or negative as the ferrous mass moves away from the pole pieces. The algebraic sign of the momentary readout will be your indication of the phase of that particular pickup.

Before someone says, "Wait a minute, the resistance of a pickup is constant, it doesn't change just because you wave a piece of iron in front of it," bear in mind that ohmmeters don't directly measure resistance. Rather, they measure the current through a resistance when a known voltage is applied and deduce the resistance from that. That current does indeed change when the piece of iron rapidly moves away from the pole pieces, just as it does when a vibrating string moves in and out above the pickup.

(This message was last edited by Te 52 at 12:18 AM, Mar 22nd, 2019)

littleuch
Contributing Member
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Ocala, Florida

Blowing bubbles
Mar 22nd, 2019 10:39 AM   Edit   Profile  

^^^Posts 2,3,4,5,7 & 8. Right there. This why this place is so great. In another place and another time the sole reply could've been "this again??".

Cal-Woody

USA/California

Why do I keep fixing things that work?
Mar 22nd, 2019 11:05 AM   Edit   Profile  

Thank you Mr. Peegoo for the humbucker pickup wiring chart. I have saved a copy and will print it out to add to my work station.
This is a real time saver and very useful for when I get instruments in for repairs.
Sometimes you get some guitars in and have to look up their websites to see the wiring charts and this will be of help.

Peegoo
Contributing Member
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Just beyond Mars

there's a world of fools
Mar 22nd, 2019 11:40 AM   Edit   Profile  

Cheers, Cal-Woody.

Another thing to do is make yourself aware of the magnetic polarity of the pickups you have. You can get a purpose-made polarity tester fairly cheaply, or you can use a magnetic compass.

Bring the compass toward the exposed end of a pickup's polepiece. If the red 'north' arrow is attracted to the polepiece, that pole is "south up."

If the north arrow is repelled by the pole, that means it's "north up."

I mention this because I have had a few guitars come in with complaints about a string sounding muffled on a specific pickup, and have discovered the polepiece was pressed in backwards, compared to the other five polepieces. This condition places that string out of phase with the other strings. This is rare, but it does happen.

It applies only to pickups with alnico polepieces, such as a vintage style Fender Strat, Tele, P/J-bass, Jazzmaster, Jaguar, or Mustang pickup. It does not apply to single-coil pickups that have steel poles and bar magnet(s)...see link.

On pickups like a standard humbucker, P90, or Filtertron, this mistake is not a factor because these pickups use a single or double bar magnet.

In a typical Gibson-type humbucker, all the screw poles will be either north up or south up, and the slug (covered) poles will be the opposite. For instance, if the screws show south-up orientation, the slug coil will be north up.

P-bass pickups (and G&L 'Z Coil' pickups) are comprized of two separate coils with opposite polarity. This configuration is partially humbucking and cuts down on noise in the signal.

Click

FDP Forum / The 'Pup' Tent / Why do some pickup combinations require flipping hot and ground?




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