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

[peskywinnets]

Why do you want to put a magnet (as opposed to a permeable magnetic material) in the bottom coil? What does its polarity have to do with anything?

Hmmm....maybe I've still not grasped this - my take was that it's the combination of both magnetic polarity and direction of coil winding that affects the signal polarity from a coil?

If that's the case, because the bottom coil is presently 'sensing' some string signal but in the opposite polarity vs the top coil (due to it being reverse wound) - I therefore need to flip that induced signal's polarity.

[Dave Kerr]

1. Magnetic shielding (to stop the upper coil magnetic field permeating down into the lower dummy coil & therefore inducing an antiphase signal ...it's this antiphase signal cancels out the main signal when summed. Truthfully, magnetic shiedding sounds like a whole new (big) area that I'm not sure I can be bothered to venture into!

It might be as simple as having a piece of magnetically conductive material in place of the separator you have now between top and bottom coil (steel shim stock, maybe, some of the other suggestions upthread?) Try making it a little wider than necessary and bend the edges up a bit after winding to tighten the flux looping around the top coil.

[Mike Sulzer]

The magnet near the string magnetizes it with a certain polarity. That is the polarity that counts.

In a side by side humbucker, the section of the string over each coil is magnetized by the magnet close to it. The magnets are opposite, and therefore the polarities of the string magnetization are also.

Hmmm....maybe I've still not grasped this - my take was that it's the combination of both magnetic polarity and direction of coil winding that affects the signal polarity from a coil?

If that's the case, because the bottom coil is presently 'sensing' some string signal but in the opposite polarity vs the top coil (due to it being reverse wound) - I therefore need to flip that induced signal's polarity.

[peskywinnets]

The magnet near the string magnetizes it with a certain polarity. That is the polarity that counts.

In a side by side humbucker, the section of the string over each coil is magnetized by the magnet close to it. The magnets are opposite, and therefore the polarities of the string magnetization are also.

But my thought goes ...... if there's a signal present from the lower coil (& there is!), then that must mean the lower coil is having a signal induced - but at the moment it's of the wrong polarity ( & therefore it's cancelling out the upper coil's signal when it's summed in that above circuit), so back to your earlier question....

Why do you want to put a magnet (as opposed to a permeable magnetic material) in the bottom coil? What does its polarity have to do with anything?

....by popping a magnet in the lower coil but of reverse polarity (vs the upper coil), the polarity of the signal from the lower coil should reverse - therefore rather than getting signal cancellation going on, I'll have signal addition (but noise cancellation). Concur?

Dave - re magnetic shielding, the problem is ferrous materials are a nightmare to cutshape! (whereas CNC'ing acrylic is easy for me - therefore I'd rather go the easiest route & design a solution around my cutting abilities!)

[David Schwab]

But my thought goes ...... if there's a signal present from the lower coil (& there is!), then that must mean the lower coil is having a signal induced - but at the moment it's of the wrong polarity ( & therefore it's cancelling out the upper coil's signal when it's summed in that above circuit), so back to your earlier question....

Stacked humbuckers do cancel out some of the string's signal, usually in the lower frequencies.

If you look at the specs on commercial unites, you often see that they are wound pretty hot to compensate for this.

....by popping a magnet in the lower coil but of reverse polarity (vs the upper coil), the polarity of the signal from the lower coil should reverse - therefore rather than getting signal cancellation going on, I'll have signal addition (but noise cancellation). Concur?

That would only make sense if the strings were under the pickup.

If you were making a pickup that didn't have to slip under the strings, then you could position the dummy coil farther way from the string sensing coil.

But still, the way it's done by Alembic with the AYX pickups, is to have the top coil with a ceramic magnet. The bottom coil just has a plastic spacer the same size as the magnet, and is wound in the opposite direction. The two coils are wound with the same number of turns, and are wired in series. Then that output connects to the preamp.

[Mike Sulzer]

....by popping a magnet in the lower coil but of reverse polarity (vs the upper coil), the polarity of the signal from the lower coil should reverse - therefore rather than getting signal cancellation going on, I'll have signal addition (but noise cancellation). Concur?

Actually, no. It is not the coil-magnet combination that determines the polarity of the signal from the coil. It is the polarity of the coil and the polarity of the magnetic field from the string that matter. Since the magnet in the upper coil is close to the string, it is the one that determines the polarity of the magnetization of the string. So only the magnet in the upper coil is important in determining the polarity of the magnetic field from the string.

This is why it is so important to understand this: the only function of the pickup's permanent magnetic field is to magnetize the string. If the string were magnetized in some other way, for example, a small magnet placed over the string, the pickup would not need permanent magnets.

[peskywinnets]

This is why it is so important to understand this: the only function of the pickup's permanent magnetic field is to magnetize the string. If the string were magnetized in some other way, for example, a small magnet placed over the string, the pickup would not need permanent magnets.

Now I know you've told me that before (& quite recently!), but it's only now that I'm at this stage of the game that what you're repeating above actually makes sense - cheers Mike!

I guess that only leave magnetic shileding between upper & lower coils as an option - hey, ho - I hate steel.


Edit: Hmm....I've pondered & repondered this one - I'm still not easy with the concept that the purpose of the pickup magnet is to 'magnetize' the string itself. Surely the purpose of the magnet is simply to create flux around the copper wire - it's when this flux gets disrupted by the vibrating ferrous string that a voltage is induced in the wire?