The 'role' of a pickup pole piece?

[peskywinnets]

Just curious... from what I can gather, the pole pieces 'project' the magnetism from the lower face of the pickup up through the 'coil' to the upper string facing side of the pickup. This in turn creates a 'flux' loop around the coil - which is what we want.

Now in the infancy of pickup design, they didn't have access to rare earth magnets...but now that we do, why not just use very weak rare earth 'rod' magnets in lieu of pole pieces?

Yes I know, some consider rare earth magnets a bit shrill in pickups, & yes, I know that a pickup will suffer strat-'itis' if the pull on the string is to great - but there again, it's now possible to get very small (weak) rare earth magnets, which would not exhibit undue pull. (I'm thinking here 1mm diameter x 2mm long)


Just wondering if pickup pole pieces serve some other purpose I'd not considered?

[Steve Conner]

They hold the top and bottom flatwork apart in a Strat.

They have machining marks on them that pickup weenies find endlessly fascinating, possibly even slightly erotic.

In a Duncan Invader, they look macho.

In Strat pickups, they ARE rod magnets: Leo stole your dinner.

[peskywinnets]

Ok, so I was thinking mainly humbuckers here!

I'm looking to make an impossibly small humbucker & just wanted to make sure I wasn't missing the point - it seems I'm not, bearing in mind the most popular guitar ever made uses a rod magnet as the polepiece!

But back to humbuckers....am I right in assuming that the pole piece purpose is soley to 'steer' the magnetic field up through the coil to the top so that the field loops back around & down to the bar magnet on the bottom?

[Mike Sulzer]

Just curious... from what I can gather, the pole pieces 'project' the magnetism from the lower face of the pickup up through the 'coil' to the upper string facing side of the pickup. This in turn creates a 'flux' loop around the coil - which is what we want.

Now in the infancy of pickup design, they didn't have access to rare earth magnets...but now that we do, why not just use very weak rare earth 'rod' magnets in lieu of pole pieces?

Yes I know, some consider rare earth magnets a bit shrill in pickups, & yes, I know that a pickup will suffer strat-'itis' if the pull on the string is to great - but there again, it's now possible to get very small (weak) rare earth magnets, which would not exhibit undue pull. (I'm thinking here 1mm diameter x 2mm long)


Just wondering if pickup pole pieces serve some other purpose I'd not considered?

1. Carry the permanent magnetic field to the string. (You got that one.)

2. Concentrate the time-varying flux from the string through the coil.

Number 2. increases the output of the pickup. The pole piece must have a permeability significantly higher than air for this to work. Neo does not. Alnico is moderate. Steel is high. Some ferrites are also high or very high.

So if you use neo magnets alone you will not get as high an output (for the same level of permanent field at the string) than if you, for example, use a small neo on top of steel or ferrite. The difference is not huge, but it could be a difference of a few times in voltage.

But the pole piece also increases the inductance. So if you do not use a pole piece you could use more turns and still keep the high frequencies. This would make up for some of the loss in output from not using the pole piece.

I think that it is best to use pole pieces.

[David Schwab]

Yes I know, some consider rare earth magnets a bit shrill in pickups, & yes, I know that a pickup will suffer strat-'itis' if the pull on the string is to great - but there again, it's now possible to get very small (weak) rare earth magnets, which would not exhibit undue pull. (I'm thinking here 1mm diameter x 2mm long)

They aren't shrill at all. On the contrary, they have a lot of low end, more than a ceramic magnet. A neo powered guitar pickup will get muddy real fast if you over wind it.

But you wouldn't want strong neo magnets as pole pieces. Since many pickups do use magnets as pole pieces, I'm assuming you meant why not use neos as pole pieces. The reason is they are too string. You can use a small neo and a steel rod though.

[copperheadroads]

I have experimented with Neos very briefly but i forget the results now ,(must not have been great ) but I'm planning on trying it in a mightymite motherbucker i got kicking around here , its a 21k mudbucker see if i can brighten that up lol

[salvarsan]

Just wondering if pickup pole pieces serve some other purpose I'd not considered?

While it's tempting to answer that any comment would be given "reluctantly", I won't.

A pole piece conducts the magnetic field toward the guitar strings.
This conductivity is called permeability and its reciprocal, reluctance.

Putting a magnetic conductor in the circuit increases the overall permeability
which, in the absence of eddy currents, increases the coil inductance and
corresponding treble roll off.

[David Schwab]

While it's tempting to answer that any comment would be given "reluctantly", I won't.

Because you are variably reluctant. This time not so much.

[David Schwab]

I have experimented very briefly but i forget the results now ,(must not have been great ) but I'm planning on trying it in a mightymite motherbucker i got kicking around here , its a 21k mudbucker see if i can brighten that up lol

Just unwind some wire from the coils. I did that to a Gibson mudbucker.

[salvarsan]

Because you are variably reluctant. This time not so much.

Is that some kind of pickup line?

[Steve Conner]

Doesn't the shape of the pole pieces also affect the harmonics generated in the output? (because the reluctance vs. string position function is affected by the shape of the tip of the pole piece)

I'm thinking of the DiMarzio Super Distortion or whatever it was, the one where each pole piece was two metal strips. And the Duncan Invader with its huge dome headed set screws for pole pieces.

[Mike McCardle]

Doesn't the shape of the pole pieces also affect the harmonics generated in the output? (because the reluctance vs. string position function is affected by the shape of the tip of the pole piece)

I'm thinking of the DiMarzio Super Distortion or whatever it was, the one where each pole piece was two metal strips. And the Duncan Invader with its huge dome headed set screws for pole pieces.

Right - perhaps the size of the head of the pole piece?

Or the fact that the pole piece is a uniform bar/blade?

I wonder what the pole pieces are typically made out of - Mu-Metal (Nickel+Iron) or perhaps just steel like in a Charlie Christian pickup?

[salvarsan]

@Steve: The shape matters whether it is raw magnet or steel pole -- some poles are designed to have greater fringe fields, particularly the Lace Sensor. More fringe fields means more flux lines for the guitar string to cross.

@Mike: Poles and blades are commonly made of soft (= low carbon) steel like 1010 or 1018, depending upon builder preference. Mu metals and similar, while superb magnetic conductors up to a point, saturate at a lower field than cheep steel and actually pass _less_ magnetic field for a given magnet.

[David Schwab]

I'm thinking of the DiMarzio Super Distortion or whatever it was, the one where each pole piece was two metal strips.

That's the Duncan Parallel Axis Trembucker.



patent #5148733

From what I remember, when they first came out it was made to work better with Floyds so that when you dive bombed the string wasn't right over the pole.

[big_teee]

That's the Duncan Parallel Axis Trembucker.

From what I remember, when they first came out it was made to work better with Floyds so that when you dive bombed the string wasn't right over the pole.

So how in the world can I make one of those.
It sure looks neat if nothing else.
I wonder what the pole pieces look like out of the bobbin.
I don't think too many folks are going to Mimic this one!
Rock on!
Terry