Get your tuts out for the lads....(re stacked humbuckers)

[peskywinnets]

Are there any tutorials wrt making a stacked humbucker? (a search on here brings up a veritable plethora of hits...but none apparently about making one)

So, if I've got the gist - a stacked humbucker is essentially two coils, one on top of the other, one coil with reverse winding *and* reversed magnetic poles? (ie assume that a single coil sound is not the end goal, where I believe they sometime dispense with magnets in the lower coil just to get the induced noise signature) )....but what gives? - if you reverse the magnetic poles of each coil, then that places two poles of the same polarity exactly above/below one another (eg say the top coil has a south pole at the bottom, then the bottom coil witll have a south pole at the top)...how does that map out then?

[Dave Kerr]

Check out Kinman's patent, 5668520, for ideas. He's got permanemt magnets in the top coil, non-magnetized slugs in the bottom, and some clever shielding to isolate them from each other magnetically.

[Mike Sulzer]

No, the magnetic poles of the bottom coil have nothing to do with it. The permanent magnet magnetizes the string. The bottom coil is too far away. Canceling hum does not involve permanent magnetism.

Are there any tutorials wrt making a stacked humbucker? (a search on here brings up a veritable plethora of hits...but none apparently about making one)

So, if I've got the gist - a stacked humbucker is essentially two coils, one on top of the other, one coil with reverse winding *and* reversed magnetic poles? (ie assume that a single coil sound is not the end goal, where I believe they sometime dispense with magnets in the lower coil just to get the induced noise signature) )....but what gives? - if you reverse the magnetic poles of each coil, then that places two poles of the same polarity exactly above/below one another (eg say the top coil has a south pole at the bottom, then the bottom coil witll have a south pole at the top)...how does that map out then?

[peskywinnets]

No, the magnetic poles of the bottom coil have nothing to do with it.

To do with what?

I was of the impression the magnets were needed to make the pickup humbucking? (or are you saying that in a stacked humbucker, becuase the poles are are too far away from the string they're not worth bothering with? If so, is an air core sufficient for the lower coil)

I'm hoping to make one over the weekend so early comments would be most welcome!

[Dave Kerr]

Think of the bottom coil more as a dummy coil as opposed to the RWRP side-by-side configuration.

[Mike Sulzer]

Magnets are not necessary to make the pickup sensitive to magnetic hum. Nor are they necessary to get two coils to cancel hum. That just requires adding the outputs of two coils that sense the hum with opposite polarity and the same amplitude. Magnetic induction works with any varying field, including current associated with electrical power.

Thus, if you leave the magnets out of a pickup, it can still pickup hum from magnetic fields. But it cannot pickup signal from the string because the string must be magnetized so that when it vibrates, there is a time-varying magnetic field.

To do with what?

I was of the impression the magnets were needed to make the pickup humbucking? (or are you saying that in a stacked humbucker, becuase the poles are are too far away from the string they're not worth bothering with? If so, is an air core sufficient for the lower coil)

I'm hoping to make one over the weekend so early comments would be most welcome!

[peskywinnets]

Great.

I'm gonna cut some bobbins tonight...the lower (noise) coil will have no core (and be slightly shallower) - the windings will be reverse wound (wrt one another), yielding...

Top Coil - positive signal, positive noise
Bottom Coil - no signal, negative noise (though slightly less due to shallower coil, meaning less windings)

I'll add the outputs from the two coils using a differential amp.... but for the lower (slightly less) negative noise signal, I will apply a little more amplification. If I get the amplification per channel balance right, the noise should cancel, leaving a relatively pure guitar signal (I'm going for low impedance, about 500 turns, 60 Ohms of 0.15mm wire)

Thanks for your input.

[Mike Sulzer]

There is one other thing to consider, and this has to do with "core or no core" in the bottom coil. A core with no permanent magnetism, such as steel or some kinds of ceramic ceramic, does increase the sensitivity to picking up stray magnetic fields. (That is, they have significant permeability.) A permanent magnet such as alnico has permeability (lower than typical steel, though) as well as being a permanent magnet. Materials such as neo are permanent magnets, but have a permeability insignificantly greater than air. So if you use no core in the bottom coil and use a core that has significant permeability for the upper one, you might have to amplify more than you want to balance out the hum. In general it is best to use a core in the bottom coil. You could even use a higher permeability material in the bottom coil to help compensate for the fewer number of turns.

Great.

I'm gonna cut some bobbins tonight...the lower (noise) coil will have no core (and be slightly shallower) - the windings will be reverse wound (wrt one another), yielding...

Top Coil - positive signal, positive noise
Bottom Coil - no signal, negative noise (though slightly less due to shallower coil, meaning less windings)

I'll add the outputs from the two coils using a differential amp.... but for the lower (slightly less) negative noise signal, I will apply a little more amplification. If I get the amplification per channel balance right, the noise should cancel, leaving a relatively pure guitar signal (I'm going for low impedance, about 500 turns, 60 Ohms of 0.15mm wire)

Thanks for your input.

[peskywinnets]

Ok, I'll slap some small metal slugs in there (but then that begs the question how to stop the magnetic field from the top coil making the 'leap' & affecting the bottom coil (which if I got any signal from, will partially cancel out the top coil's signal when I add them together in the differential amp).

Ok, my bobbins are cut....3mm high (1/6") for the bottom coil and about 4.2mm high for the top coil (ie very small at about 7.2mm High in total (which is just under 5/16") ......& with 3mm (1/16") upper coil pole pieces .

The bobbins are brown bits being held in place on my winder backplate & blue plates here...




...it'll be bobbinless, hence not having any outer edges! I'll wind it tomorrow.

[David Schwab]

Ok, I'll slap some small metal slugs in there (but then that begs the question how to stop the magnetic field from the top coil making the 'leap' & affecting the bottom coil ...

Here's a DiMarzio Virtual Vintage.

Steel slugs in the bottom coil, and a magnetic shield between the two. The bottom coils is also wound with less turns of larger diameter wire.

[peskywinnets]

Here's a DiMarzio Virtual Vintage.

Steel slugs in the bottom coil, and a magnetic shield between the two. The bottom coils is also wound with less turns of larger diameter wire.

That's interesting & flies in the face of what I'd thought. Since my lower coil is physically more squat, I'd reckoned on using thinner wire vs the top coil (kind of "Never mind the size, feel the quality" - which I get used to saying a lot)


What's the gerneral consencus on a suitable material to use for magnetic sheilding (ie using materials that are accessible - my local mu-metal shop on the corner closed a couple of months ago - they couldn't wait for me)

[Steve Conner]

Mu-metal is a bit impractical anyway. If you bend it or hammer it, it loses its magical magnetic properties and has to be annealed in a hydrogen furnace to restore them.

Soft iron, as used in transformer cores, would probably be best. But I'm sure ordinary steel would work reasonably well. If you dismantle an old hi-fi amp, sometimes you can find a magnetic shield made of iron sheeting wrapped round the transformer, and that would certainly be the right kind of iron for the job.

[peskywinnets]

If you bend it or hammer it, it loses its magical magnetic properties and has to be annealed in a hydrogen furnace to restore them.

Wouldn't be a problem - we have a halogen hob [typed in a deadpan manner]

Soft iron, as used in transformer cores, would probably be best. But I'm sure ordinary steel would work reasonably well. If you dismantle an old hi-fi amp, sometimes you can find a magnetic shield made of iron sheeting wrapped round the transformer, and that would certainly be the right kind of iron for the job.

I guess I need to subscribe on a 'Magnetism for Dummies' course at our local evening classes....becuase I'm wondering how something that's ferrous stops the magnetism permeating from the top (active signal coil) through to the lower (dummy) coil's steel pole pieces? And if that happens, then I'm gonna get signal cancellation when I add them together in the differential amp (bearing in mind the lower dummy coil won't have magnets - I could add magnets to reverse the signal polarity & avoid signal cancellation, but that's where I came in at the top of this thread - ie how to stop top coil & lower coil magnets fighting one another in a stacked humbucker arrangement?)

[Mike Sulzer]

The shield tends to guide the field lines coming from the string (and passing through the upper coil) away from the lower coil so they can loop back up to the string.

Putting permanents on the lower coil does not stop signal cancellation.

Wouldn't be a problem - we have a halogen hob [typed in a deadpan manner]



I guess I need to subscribe on a 'Magnetism for Dummies' course at our local evening classes....becuase I'm wondering how something that's ferrous stops the magnetism permeating from the top (active signal coil) through to the lower (dummy) coil's steel pole pieces? And if that happens, then I'm gonna get signal cancellation when I add them together in the differential amp (bearing in mind the lower dummy coil won't have magnets - I could add magnets to reverse the signal polarity & avoid signal cancellation, but that's where I came in at the top of this thread - ie how to stop top coil & lower coil magnets fighting one another in a stacked humbucker arrangement?)

[David Schwab]

That's interesting & flies in the face of what I'd thought. Since my lower coil is physically more squat, I'd reckoned on using thinner wire vs the top coil (kind of "Never mind the size, feel the quality" - which I get used to saying a lot)

Thinner wire has higher resistance, so it's going to alter the tone of the top coil more.

You want the dummy coil to be high in noise sensitivity without messing with the tone of the top coil too much. I've installed a few of those Dimarzio pickups for customers and they sound very good.

What's the gerneral consencus on a suitable material to use for magnetic sheilding (ie using materials that are accessible - my local mu-metal shop on the corner closed a couple of months ago - they couldn't wait for me)

Most of these pickups use thin steel. I've done some experimenting with shields and use that thin steel shielding you find inside of computers.