Magnets as pole pieces, *and* slugs?

[j. pierce]

Hi. Long time lurker, first time poster.

I've got a few winds under my belt (been practicing with old dead plastic bobbin strat-knock off pups and a stew mac humbucker kit.) and have tried my hands at making my own flatwork bobbins with some success.

I'm a hobbiest guitar builder (more a "guitarpenter" than a "luthier") and I'd like to make some from scratch pickups for the two builds I have going - a bass and a guitar. (Both instruments are routed for standard pickup sizes, so if something goes horribly wrong, I can still purchase and mount aftermarket p'ups.)

Anyway, my question - I've got a set of six A5 rods for a strat style p'up. I was thinking at perhaps trying to make a humbucker, but with magnets as pole pieces rather than slugs and screws connected to a bar magnet below. Almost like two single coils, I suppose. I remember having a pickup built like this once and really enjoying the sound of it.

However, I've only got 6 magnets. I do have some steel humbucker-style slugs, however. I'm wondering if I can't use these as the pole pieces in the second coil, and make a steel spacer of sorts to connect the magnetic field from the A5 rods to the slugs.

Am I totally off-base here?

Do I misunderstand the way the magnetic fields would work in this instance?

Would this just sound terrible?

How large a piece of steel do I need to use? Could I cut something from a medium gauge ferrous sheet metal, or should I really use rod stock?

Just to make this interesting, this is going to be sized to fit in a P-90 route. I have enough wire kicking around right now, that even if this works out to be total bunk, I'm okay just building or buying something normal and chalking this up to experience.

I'm not shooting for a particular sound right now, just "not awful". Although I'd like something with a little bit more chime than a standard 'bucker.

I tried searching through the boards here, which has answered most questions I've had in the past, as I'm sure this has probably been covered before; but this is one of those subjects where the search terms end up being vague enough I'm having a hard time finding an applicable thread. If someone can point me to where this has been covered before, I'd gladly appreciate it!

[black_labb]

i dont know how the connection would work, but worst case scenario it can work as a dummy coil. give it a try. try in series and paralell before you decide against it. i'd probably bend a piece of steel to use as the second poles (maybe sheet steel as opposed to rods), so it is the same piece, making a proper magnetic connection.

im sure someone else will chime in as to wether it will work. one thing is i dont think the slug coil will have much strength magneticall at all.

[salvarsan]

one thing is i dont think the slug coil will have much strength magneticall at all. Magnet energy per unit volume is consistent enough for rough estimates.

The PAF bar magnet is 2.444" x .492" x .127" and the 6 pole pieces are .1875" diameter by .625" length.

The PAF magnet volume is .152 ci, while the pole pieces are .104 ci.

You can estimate that, for a given magnetic alloy,
a PAF bar has 50% more magnetic energy than 6 SC pole pieces.

If your slugs are magnetically connected to the magnets.
your design should work well enough to develop into a product.

-drh

[j. pierce]

Thanks folks!

Magnet energy per unit volume is consistent enough for rough estimates.


Ah, that hadn't even occurred to me! I don't know nearly enough about how magnetics work.



The PAF bar magnet is 2.444" x .492" x .127" and the 6 pole pieces are .1875" diameter by .625" length.

The PAF magnet volume is .152 ci, while the pole pieces are .104 ci.



Isn't the formula for a volume of a cylinder pi * radius squared * height ? I'm not sure how you get the .104 unless I'm doing something wrong. (Which I very well may be - It's been a long time since geometry!) I get about .0173 ci - which would put me with quite less magnetism than a bar magnet, I assume.

But if the principal is functional in the "it'd probably produce sound" sense, maybe I'll play with it. It lets me wind with what odds and ends I have around here, and worse case scenario I get a working single coil and half of a humbucker for future use, I guess.

[David Schwab]

I was thinking at perhaps trying to make a humbucker, but with magnets as pole pieces rather than slugs and screws connected to a bar magnet below. Almost like two single coils, I suppose. I remember having a pickup built like this once and really enjoying the sound of it.

Duncan has the Stag Mag, which is a humbucker with alnico rods instead of screws and slugs.

If the bottoms of the rod magnets and slugs touch the steel spacer, that should work. Just don't extend them past the keeper plate, and I wouldn't have the plate wider than the mags/slugs. You don't want it like a regular humbucker, where the magnet touches the sides of the poles. You want a U shape, not an H. The slug side wont be as strong, but it will work.

I have a pickup I made just like this (six mags, and six slugs) in a guitar of mine.

[salvarsan]

Isn't the formula for a volume of a cylinder pi * radius squared * height ? Yup. I'm not sure how you get the .104 unless I'm doing something wrong. (Which I very well may be - It's been a long time since geometry!) I get about .0173 ci - which would put me with quite less magnetism than a bar magnet, I assume. 6 pole pieces means (6 * .0173) = .1038 ~ .104

How many pole pieces will be in your pickup design?

-drh

[j. pierce]

Yup. 6 pole pieces means (6 * .0173) = .1038 ~ .104

How many pole pieces will be in your pickup design?

-drh

Ugh. Sorry, I don't know what happened there! Yeah, 6 seems like a good number, huh?

I kept looking at my numbers, thinking I'd missed something, and totally overlooked the obvious!

The only reason I did the math was because I had slightly longer pole pieces. I just got off work, and I guess I should know better than to try simple equations after a long night shift.

Thanks again for the guidance.

[David King]

You could always bump up the magnet diameter to 5 mm or 1/4" if you needed more oomph - assuming your wire will still fit...

[SK66]

I don't see the problem being with "magnetism" as such, but with the resulting field's shape.

You will have to create a method to transfer some magnetism from the poles to the slugs, a simple carbon steel plate which they BOTH sit on would work. You would ideally need perfect contact to transfer the most energy, and a way to eliminate vibration in the assembly that doesn't hinder transfer of magnetism. I think this is reasonably doable.

What WILL result is a much stronger and focused polarity at the polepiece side. You will get something like a narrow aperature HB sound, or a wider singlecoil sound. Not that that's a bad thing.
You can then adjust "coil output" individually to tailor the sound, but you might very well find that "matched coils" will sound very good in such a design.

[black_labb]

what about using screws like the screw side of a hb, and threading the plate that is under the magnetic poles. this would ensure connection between the plate and the poles, and the magnet should hold the other connection correctly.

[SK66]

That should work fine, but a bit more difficult to acomplish.
The size and length of the piece(s) of metal used will affect the resulting field as will the final shape of the assembly.

[black_labb]

the only extra thing you would need is a tap for the screws, and most people who make buckers have one to thread the bobbins and base plate.