question about pickups and phase

antichef

antichef

pornk rock
I have a sg clone with two P94 pickups (humbucker sized single coils). It has a three way toggle switch, and I wired the pickups so that when the switch is in the center position, both pickups are active and are humbucking each other. Sure enough, the single coil hum you can hear when either pickup is selected totally goes away when they're both active, provided the two volume knobs are in similar positions (i.e., turn down one of the pickups and the hum from the other one returns).

Anyway, I kind of like the two-pickup sound, but there's a hollowness to it that I now associate with phase issues when I'm recording using two mics in the wrong places. Could this be happening? If so, is there any way to deal with it by perhaps slightly adjusting the phase of one of the pickups?
 
Is it really thin and lacking bass, or just kinda phasey sounding? Better yet, grab a screwdriver, plug the guitar into your computer, open your recording software and hit record. Switch to one of the pickups. Very slowly put the screwdriver against the pole piece of the selected pickup and then quickly pull away. Switch to the other pickup and repeat. Now inspect the waveform. Do both pull offs swing the same direction in the display?

There isn't a good way to "slightly adjust" the phase of the pickups with respect to one another. You can flip the absolute polarity, and that's about it. If they are both the same, then the fundamental of any note you play will always be in phase between the two pickups. Every other harmonic of that note will have some amount of phase shift between the two pickups, but this relationship depends on the relation of the vibrating length of the string to the pickup spacing and is therefore different depending on where you fret.
 
In fitting pickups you can choose magnetic polarity (physical orientation) and electrical polarity (wiring orientation).

Two choices for each = four options total.

If this makes any sense ( MP=magnetic polarity, EP=electrical polarity )


MP_____EP
++ and ++ = strong output with hum
+- and +- = strong output without hum (what you want)
++ and +- = weak output without hum (what you seem to have)
+- and ++ = weak output with hum

In short, one of your pickups is probably the wrong way around. :)
NB: If you invert all the polarities in this chart it's still true, so it shouldn't matter which pickup you rotate.

I hope I got that right. :facepalm:
 
Steen, I may be misunderstanding your chart, but it looks misleading at best and plain wrong at worst.

First, "electrical polarity" is better referred as "winding direction", as the polarity of the signal depends on both magnetic polarity and the winding direction.

Next, in order to get "strong output no hum" both magnetic polarity and winding direction must be opposite polarity. Oh wait! Just figured out your table. I thinks it's right... Sorry. My first point though...

It also sounds like you suggested physically rotating the pickups to fix issues. That won't do any good, of course. Depending on which is the problem you would need to either rewire or remove and flip the magnet.
 
thanks guys - this is starting to make sense to me (except I don't yet get the chart). These are big fat single coil pickups, and I assume they're wound the same way. I can't remember the colors, but let's say there's a white and black wire coming out of them. I intentionally wired the black wire from one and the white wire from the other to the same place (and vice versa), because that's what I understood I needed to do to get humbucking.

It does kind of make sense that doing that would invert the phase of one of them relative to the other. But is there any other approach? seems like if I did white/white black/black, I'd get stronger output, but double the hum (?).

Also, unlike a regular humbucker, these two are far apart from each other (specifically, in the bridge and neck pickup slots). Could that be an issue that would make them create some phase cancellation that wouldn't occur in a regular humbucker?

edit - now I think I get the chart - I reversed the electric polarity (EP) for one of the pickups by swapping the wires, but I didn't also reverse the magnetic polarity (MP), resulting in the ++ +- quadrant - is that right? Also, sounds like I'm hosed :) (unless I dissect one of them to reverse the MP)

edit2: more clues: http://www.gibson.com/Files/Downloads/PDFs/Diagrams/PUPwiring.pdf -- I believe this what I went off of when I installed them. I'm not sure if I have the two different types of P94 (T and R - looks like this very issue is addressed that way) but I'll try and check somehow.
 
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ashcat_lt said:
Steen, I may be misunderstanding your chart, but it looks misleading at best and plain wrong at worst.
.............
It also sounds like you suggested physically rotating the pickups to fix issues. That won't do any good, of course. Depending on which is the problem you would need to either rewire or remove and flip the magnet.
Click to expand...

I'm pretty sure it's just misleading. :p

You're right about the last part for sure. I did word that very badly. I was being flippant, but I should have said magnet.
 
ashcat_lt said:
Next, in order to get "strong output no hum" both magnetic polarity and winding direction must be opposite polarity. Oh wait! Just figured out your table. I thinks it's right... Sorry. My first point though...
Click to expand...

Sounds like you have opposite winding direction,(which you want) but not opposite magnetic polarity.

You're right, I think. If you swapped your wiring you'd probably get hotter (fuller) output and hum which is of course what single coils are known for. :p

Ashcat, keep me right here, but OP either needs to swap wiring on one pickup and make do with the hum, or flip the magnet in one pickup, if possible, right?
 
Also - I was a little misleading - I wouldn't call it weak output, it's close the same volume as the two alone. It's just that it seems like there's some comb filtering or something, if that makes sense.
 
You can't flip the magnet in a single coil pickup because the pole pieces are the magnets.
 
Steen (and OP) - the hum cancelling indicates that it is RW, the fact that it's not noticeably weaker indicates that it may also be RP, and this is just how they sound when combined. The screwdriver test could illuminate the issue pretty well, or you could try pushing the two pickups together face to face. Opposites attract after all.

Ocnor - not necessarily the truth. I think of all the SCs in my various guitars I don't actually have a single one with permanently magnetized pole pieces.
 
gerg - I haven't played true P90s enough to really say. I don't notice a difference, but there must be at least a small difference due to the shape.
 
actually, I downloaded a software oscilloscope, and the screwdriver test became doable - here they are:

the bridge:
bridge.png

and the neck:
neck.png

they look the same, no?
 
Yeah. Maybe that's just how they sound together then.

Anyone; I take it it's normal for a pair of single coils to have their magnets opposing from the factory?
 
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