What can make a humbucking pickup hum?

[David Schwab]

We hear the harmonics of 60 Hz far better than 60 Hz itself. Same for 50 Hz.

Right, and when power supplies are full wave rectified the 60 Hz is doubled to 120 Hz. 60 Hz is hard to hear. Even on a bass guitar you are mostly hearing the harmonics.

[Joe Gwinn]

Right, and when power supplies are full wave rectified the 60 Hz is doubled to 120 Hz. 60 Hz is hard to hear. Even on a bass guitar you are mostly hearing the harmonics.

It's more complex that that, even. The brain synthesizes the missing fundamental from the harmonics. So, we hear the 60 Hz, even though it isn't really there.

[David Schwab]

It's more complex that that, even. The brain synthesizes the missing fundamental from the harmonics. So, we hear the 60 Hz, even though it isn't really there.

Right, assuming you have the upper harmonics. That's how telephones work. But if you take a sine wave at 60 Hz, it's not very loud compared to something with more harmonics.

Getting back to this, I have a guitar with three single coil size humbuckers. I made the neck pickup, the center is an old Lawrence L-250, and the bridge is some off brand Asian pickup. That one hums a little at high gain, and the other two are dead quiet. I'm going to take it apart to see why it's humming. I'm thinking maybe the blades aren't grounded, but I don't know yet.

If a humbucker is humming a lot, I'd check to see if the two coils are out-of-phase as they are supposed to be. Don't always trust the wiring either, because if the bobbin is wound backwards or flipped over it will hum. It will also sound thinner, but sometimes you can't tell until you flip it the other way.

[Boogie]

No i didnt try the other coil together with the single coil pickup - that would be a very good idea.

I didnt know that about the bad joint can be there and stuff up the inductance but not the resistance - though I was suspicious of something like that because I cant think what else it could possibly be (or something wrong with the actual coil itself along similar lines that has managed not to change the resistance

What about wax potting? though i would have thought if it was potted too hot and melted some of the insuation on the coil windings themselves that would drop the resistance....

re 60 vs 120 cycle hum - i agree its broad spectrum EM interference - though i did notice (and didnt mention before now) that the hum of the humbucker does sound a higher pitch overall (like maybe by an octave, like double)than the hum of the other single coil pickups on their own
. and i wondered what could cause that??

They are definitely correct re the phase of the wiring since i tried all possible ways for series wired coils (the order of the coils and the direction of both together, and phase between them by swapping the direction of just one). with the wrong phase the hum was obviously louder than one s/c pup on its own, and approx 2-3x as loud as the humbucker on its own when wired with the proper phase

When I get to the shops for some 4 conductor cable i'll try it with that and also try just one coil (but the other one) in parallel with the single coil pup . i am aware that the other coil needs to be the opposite direction/phase to the one i tried to cancel hum with the other pup (compared to how it would be wired in the humbucker - which is the same direction as the other coil in terms of physical direction - which is hard to explain but i know what i mean, lol)

if the pickup is quiet with just one coil from the humbucker together with the middle s/c pup, can there still be anything wrong with the guitars wiring?

the only unusual wiring in the guitar is that it was factory wired for the monstertones , which are tapped single coils, and the 5 way switch is wired using both sides of its double poles, one pole for the tapped hot leads and one for the full coil hot leads, then the two output hot leads from the switch, one from each pole, go to a push/pull pot switch that picks one of the other for full vs tapped pups.

so when i finally get a working humbucker (either this one fixed or another) i will have that as a coil tap (for one coil vs two) and then i can get the "quack" sound from bridge and middle single coils, or the humbucker alone, or just one coil of the humbucker (or both coils of the bucker plus the middle pup but this is a pretty crap sound).... still that would give me three nice fully humbucking sounds (four if you count tapped vs non tapped for the bridge plus middle as two sounds). plus all the single coil sounds that i cant really use live unless with a totally clean (no distortion) guitar sound

i plugged in my epi les paul after all the pickup experiments and noticed that the humbuckers in that do hum slightly too - WAY less than the EVH one, but more than the two schecter s/c pups in parallel. the les paul with both buckers on together in parallel was a lot quieter than with just one pup on.

is it true that wiring two coils in parallel will cancel hum better than wiring them in series? i guess if there were phase issues created by the slight delay of the signal going through the inductance of the coil, or its internal capacitance, or something, then parallel would cancel that better --- since in parallel the signals would be generated by each coil at the exact same time, but in series it would be like first through one coil and then the other, so there might be a slight mismatch of the phase which would not 100% cancel

[Boogie]

the other s/c pups in the guitar are not shielded that much better than the uncovered EVH bucker and they are almost perfectly quiet together in parallel. and they are physically a lot further apart than the 2 coils of the bucker, which i thought was meant to be a lot worse for hum cancellation

the monstertones have a copper strip over the outer edges of the coils, i cant remember if this is grounded or not (it seems logical that it would be) so i guess that would shield them a bit, but the tops are still fully unshielded. the bottoms are too but the cavity of the guitar (including the pup cavity) has conductive paint

the EVH pup with both coils on in the normal way sounded good and loud, there was nothing wrong with the signal, apart from the hum

[Mike Sulzer]

"is it true that wiring two coils in parallel will cancel hum better than wiring them in series?"

Either way works fine.