How do stacked humbuckers work?

[rbkxiiowe]

Hello. Another silly question:

Stacked humbuckers have a coil on top wound one way and a coil underneath wound t'other, right? But do they also have reverse polarity magnets for each coil? Is a magnet needed in the coil to buck the hum or is it only the coil itself that senses the outside noise?

[ChrisK]

Stacked humbuckers have a coil on top wound one way and a coil underneath wound t'other, right?

Yep.

But do they also have reverse polarity magnets for each coil?

Maybe, maybe not.

Is a magnet needed in the coil to buck the hum

Nope.

or is it only the coil itself that senses the outside noise?

Yep.

[rbkxiiowe]

Quote:
But do they also have reverse polarity magnets for each coil?

Maybe, maybe not.

Why maybe? Wouldn't the bottom magnets interact with the top 'uns and send the flux-ey stuff all screwy? And if the bottom coil has a magnet and picks up the strings wouldn't that also cancel some of the top coil's signal? And if the bottom coil & magnet doesn't pick up the strings, what's the point of it being there?

[andy]

I'm not sure about the flux issue- however I think the second coil is often shielded from the strings as best possible, as a stack is usually to cancel the hum but retain a single coil tone. The other coil is there to cancel the hum, not to pick up any extra string vibration (I think!). Thats why stacks tend to be vintage alike and side by side single-coils-sized-humbuckers are usually more 'humbucker' alike.

That second coil is almost a built-in dummy coil, I suppose.

[ChrisK]

There is no simple answer. There are many designs afoot.

In some cases, the top coil is the sensing coil and the bottom coil only senses the hum which is subtracted from the top coil. A case in point was (was, it's dead now) the DiMarzio HS1 which had an output of about 100 mV or so but a combined coil resistance of 27K (well, there goes the "my pickups are so hot 'cuz they have 15 K's of output").

In some cases the two coils are wound to pick up hum as equally as possible, but to sense the strings as unequally as possible. When only a single coil is selected, they are hotter than in humbucking mode. When the two coils are wired electrically out-of-phase, small children melt. Think of the Fender Hot Noiseless.

Some are even more different. The Fender SCN pickups have permalloy slugs under the strings and four samarium cobalt bar magnets between the two coils, not unlike a P-90 structure. This can be verified by testing each end of the slugs with a polarity detector. On my AmDlx Strat, both ends show North and the sides of the pickup shows South.


Go to www.uspto.gov and search patents by inventor name or assignee. Of note is DiMarzio and Duncan Carter (or, uh, Leo). If one can't figure out how to do this, one isn't going to understand the patents either.


There are many pickup patents that teach much. Finding a later one will give a trail backwards by cited references. Once you find a juicy one, go to www.google.com/patents and enter the patent number. It will give you hits by cited references.

[rbkxiiowe]

Cheers Chris, that's good info.

Just found www.kinman.com/html/myProducts/strats.htm#Stratsecrets, which answered a few questions too.