how do stacked humbuckers actually work?

[Arx]

Every piece of info I can find on humbuckers explains regular ones reasonably well. Magnets reversed, winding reversed.. Makes sense. No problem.

Most of those same articles also mention stacked humbuckers, but just say that they're the same thing with the two coils stacked.

How does that work? Coil is reversed but the magnet isn't. Shouldn't that cause a lot of cancellation?

Is it simply that the second coil is further away and picks up less of the signal from the strings?

-Nick

 

[Arx]

bump.

 

[scottyd]

I've built a couple of sets. I build mine like this, 3 flats per bobbin, Long magnet poles that go through all 3, imagine a regular coil with a flat in between the top and bottom to separate them to make 2 coils. Wind both coils and wire them like you would any bucker.
Essentially it’s just a bucker that shares the same poles. On my last set I wound each coil with opposite rotations. I really don't think that’s necessary though.

Here's a set I wound back when I was still using wood for bobbins (seems so long ago!) The guy who owns the bass that this set is in says he gets a lot of compliments on his tone.

 

[Rune Bivrin]

It's hard to see how that could actually "buck" any hum, though. The coils have the same direction for both the magnetic flux from the poles and any ambient magnetic fields.

 

[pilotjones]

Yeah that's what I am not getting... the magnetic polarity is the same on both coils, and I think they are seeing the same field and field variations... so, you could either wire the two coils same winding direction (cw or ccw), thus adding the signals and the hums, or opposite winding directions, and cancel both the hum and the signal. Am I missing something here?

 

[Phil Mailloux]

The coils are wound in the same direction but connected to each other to let the current flow in opposite direction. That'll reduce the hum.

On a lot of stacked humbuckers, the lower part of the coil is just unmagnetised slugs where the top part will have the magnets. There's a couple of different ways of making them. You can find out more about them by searching the US patents website. The patent Chris Kinman applied for some years ago is pretty interesting to read up on.

 

[Arx]

scotty: Yeah, I can say that the ones you wound with the same direction on both are essentially single coils with an extra chunk of wood/plastic in the middle.

pilot: with the reverse wound bottom coil, I guess the string must just be far enough away from the bottom coil that the cancellation isn't too strong.

In that case it's pretty much the gradient that's getting the job done, it's probably better just putting an identical reverse wound coil a couple inches away (separate bobbin), or behind a magnetic shield, with either no poles, or non-magnetized poles on the bottom half.

-Nick

 

[Arx]

The coils are wound in the same direction but connected to each other to let the current flow in opposite direction. That'll reduce the hum.

On a lot of stacked humbuckers, the lower part of the coil is just unmagnetised slugs where the top part will have the magnets. There's a couple of different ways of making them. You can find out more about them by searching the US patents website. The patent Chris Kinman applied for some years ago is pretty interesting to read up on.

True. I guess reverse wiring would be the same as reverse winding.

I would want shielding though, or your non-magnetized slugs will conduct the field through the rest of the coil.

 

[scottyd]

scotty: Yeah, I can say that the ones you wound with the same direction on both are essentially single coils with an extra chunk of wood/plastic in the middle.

You can say that but you'd be wrong! When you reverse the way the coil is wired, it is the same as reverse winding. That bucks the hum....


PILOT:
It's my understanding that you only need different magnet polarity orientation between coils in a parallel situation. Such as a Jazz bass that has 2 single coils with 2 vol setup. When both vols are turned up both of the coils are in parallel, the hum won’t cancel in parallel by wiring alone, so to make it the magnets need to be north up on one coil, south up on the other to do the hum canceling voodoo magic. Searcy would be the man to contact to confirm this.

 

[pilotjones]

Actually, per my understanding of it,
- it works in parallel or series
- the two coils, regardless of which way the magnets are polarized, act as antennas. By wiring then so that the "normalized" plus-to-minus current is cw on one and ccw on the other, the two noise signals will cancel. (This can be done either by winding them opposite directions, mounting them in the same direction, and using both coil starts (or finishes) as plus; or by winding them the same direction, mounting them in the same direction, and using the start of one coil and the finish of the other as plus; or by winding them the same direction, flipping one upside down, and using both coil starts (or finishes) as plus.)
- since the coils are running opposite directions (cw & ccw), the audio signals would also cancel--unless you also reverse the magnetization in one coil, which is what is done. That's why they're called a RPRW set. One coil is reverse would and reverse polarized (magnetically). The reverse wind makes the noise signals cancel, but the reverse polarity re-reverses the audio signal, so they add instead of cancelling.

 

[Gone]

Here's a set I wound back when I was still using wood for bobbins (seems so long ago!) The guy who owns the bass that this set is in says he gets a lot of compliments on his tone.

btw, what's the issue with using wood for bobbins?
I was planning on doing so for my first attempt at pup winding.

 

[Arx]

You can say that but you'd be wrong! When you reverse the way the coil is wired, it is the same as reverse winding. That bucks the hum....

Yeah, I caught that aspect in Phil's email. I stand corrected.

PILOT:
It's my understanding that you only need different magnet polarity orientation between coils in a parallel situation. Such as a Jazz bass that has 2 single coils with 2 vol setup. When both vols are turned up both of the coils are in parallel, the hum won’t cancel in parallel by wiring alone, so to make it the magnets need to be north up on one coil, south up on the other to do the hum canceling voodoo magic. Searcy would be the man to contact to confirm this.

Doesn't matter if they're parallel or not. Hum will cancel any time the coils are wired reverse to each other. The magnets have no effect for hum. The whole idea is that you have the two coils reversed so when they pick up noise, they pick it up exactly opposite to each other. When you add them you get zero. NO HUM.

unfortunately reversing the coil will also reverse the output of the coil, so you also get no sound (at least in theory). The way you get around this is by also inverting the magnetic field, so the pickup will get the signal reversed. It gets reversed twice, and ends up straight again.

Your signals add, but the hum will subtract.

A stacked humbucker relies on a slightly different effect, since by this simplification you should get absolutely no output.

My theory is that the second coil being further away causes less pickup in the second coil. Really it's acting as a dummy coil. Any vibrations it actually does pick up are actually hurting the output of the pickup.

 

[pilotjones]

Agreed, pretty much what I said, Nick, except that I think the second coil should see substantially the same field (and variations) as the first, since the polepieces draw the field down. I can't imagine how you'd get any output unless you did something to change the fields in the two coils (such as polepiece gap with steel separator, or two pairs of polepieces with opposite magnetizations back to back maybe). Or unless the two wings were unbalanced, in which case they'd fully cancel neither the audio signal nor the hum.

 

[scottyd]

Maybe you guys should just build some, they work and they work well thats all I need to know!

btw, what's the issue with using wood for bobbins?
I was planning on doing so for my first attempt at pup winding.

None, wood works great. I just started using acylic instead, I can get the flats thinner that way and in turn a smaller coil.

 

[Arx]

Maybe you guys should just build some, they work and they work well thats all I need to know!



None, wood works great. I just started using acylic instead, I can get the flats thinner that way and in turn a smaller coil.

Yeah, but knowing how things work allows you to make them work better.

I bought some lexan (polycarbonate). You can drill it with ordinary drill bits and not crack it.

 

[Son of Magni]

...The whole idea is that you have the two coils reversed so when they pick up noise, they pick it up exactly opposite to each other. When you add them you get zero. NO HUM.

unfortunately reversing the coil will also reverse the output of the coil, so you also get no sound (at least in theory). The way you get around this is by also inverting the magnetic field, so the pickup will get the signal reversed. It gets reversed twice, and ends up straight again.

Your signals add, but the hum will subtract...

This is pretty much the clearest description of how it works.

Agreed, pretty much what I said, Nick, except that I think the second coil should see substantially the same field (and variations) as the first, since the polepieces draw the field down. I can't imagine how you'd get any output unless you did something to change the fields in the two coils (such as polepiece gap with steel separator, or two pairs of polepieces with opposite magnetizations back to back maybe). Or unless the two wings were unbalanced, in which case they'd fully cancel neither the audio signal nor the hum.

Yeah, so my guess is that the pole pieces do not penetrate to the bottom coil at all. Also the bottom coil doesn't want a magnet. It's just a dummy coil like the way Alembic used to mount a dummy coil in between the two pickups. Think about it this way, make a single coil pup, then under it stick another winding with no pole pieces or magnet.

 

[Arx]

Yeah, so my guess is that the pole pieces do not penetrate to the bottom coil at all.

But they do in a lot of them, and they do seem to work. That's what I'd like to hear an explanation for.

-Nick

 

[pilotjones]

+1

 

[Svenson]

Discussion just made me curious, so I had a brief look at a commercial J-Bass pickup of a well-known manufacturer. Despite the pickup has the design of a single coil pickup, denoted as humbucker, it's a P-Bass configuration in a J-Bass package: Two coils with different oriented magnets, one coil for E and A, one coil for D and G. Thus, as in a "classic" humbucker configuration, hum cancels, signal not doubles. That's it, no miracles, and it really works

 

[asad137]

There's an interesting discussion of stacked humbuckers in the article linked below (yeah, it's about guitars...sorry, couldn't find a bass-specific one )

http://www.soundonsound.com/sos/nov98/articles/pickup.htm

The most pertinent section is in the 2nd blue box on the page:

In essence, the principle behind the stacked-coil humbucking pickup is that it relies on only the top coil sensing the string, thereby producing something like a normal single-coil sound, whilst the bottom coil only picks up induced noise which is used in antiphase to cancel the noise also picked up by the top coil. However, in practice, it is not quite so simple. With both coils in close proximity and wound around a common magnet structure, interaction is inevitable, and the simple fact that the two coils are connected together changes the the DC resistance, altering the inductance, and thereby the resonant frequency... I could go on, but you've probably got the point!...

Asad