Magnetic anomaly inside a Delano bass pickup

[tubby.twins]

I asked Delano to make a me a custom pickup in the P2 shape, as a twin coil in-line humcanceller. I requested this because I previously bought their "MC5 HE" double twin coil in-line humcanceller pickup, and really enjoyed the tone produced by the "north" half of the pickup at a specific location. The custom pickup arrived today. This is what my magnetic paper shows on the "north" surface (i.e. the side facing the neck) of this new custom Delano "SMC5 HE" pickup. (Please forgive the inclusion of my lumpen fingers.)



I've never seen that circular pattern in the magnetic paper before, and I've tested quite a number of bass humbuckers. I also tried my "screwdriver" test, where I lightly drag a small steel screwdriver across the surface. At this spot, the screwdriver wanted to "jump" over and continue on past the circle. It's the oddest thing I've ever seen!

I tried to use the magnetic paper to test my existing "MC 5 HE" pickup, but couldn't find this kind of spot on it. (I'll try again when I get a chance to remove it from its bass.) The same holds true for my other Delano "SBC driver" pickups (dual-coil and quad-coil humbuckers in P2 shell).

The magnetic paper shows the top surface as normal - there appears to be a single magnetic region which spans most of the top of the shell, but shifted slightly "north". (Carvin's H50AS "stacked coil" humbucker appears the same way. I think the armature is simply intended to be offset from the centerline of the shell.)

As a point of note, when I ordered this pickup, I was asked by Delano if I wanted to be able to use this pickup with any other pickups. I answered "no" since it was intended for a single-pickup bass. Now I am wondering whether this had anything to do with this magnetic anomaly, and what would have happened if I answered "yes" instead. I've read earlier posts which seem to indicate a difference in magnets and windings between their "humcanceller" and "humbucker" pickups, but I didn't know if this particular anomaly was part of that difference.

And by the way, the pickup sounds just fine. I was just puzzled by what I saw, so I thought I'd ask the forum. Any ideas?

[David King]

It looks like a small neo disc that's energizing the rail.

I can't explain the screw driver wanting to "jump' over it - unless the screw driver is magnetized...
My guess is that there would be another one on the other side, on the other coil's rail.

[tubby.twins]

I didn't see any other spots like this one. If there's another Neo disc magnet inside, it may be too far from the edge to detect.

The screwdriver does the "jump" if I move it quickly, but maybe that's because it carries a residual magnetic "charge" from the previous region. I see that effect with a more "typical" dual coil (parallel) humbucker, as I move the screwdriver from one "coil" to the other.

If I move it more slowly across this region, it does a shorter jump across the boundary to enter the region, then jumps out again as I pass over the opposite boundary. This leads me to believe there is a fainter field of the opposite pole surrounding the region on both sides.

Is this a typical strategy (using neo discs on the side)? I was under the impression that most rails were uniformly magnetized across the bottom. This thing, though - it's starting to make me really curious. None of my other Delanos have anything like this.

[David Schwab]

That's very odd.

I know he has a number of pickups that don't work with other types. I think the reason is half of the pickup would be out of phase. I figured he was doing a split coil setup, but with the same magnetic polarity on both halves.

Do you have a compass you can pass over parts of the pickup to see the magnetic polarity?

You can also try this:



[yeah, I've used this picture before... but it's still funny to me]

[Sweetfinger]

That's very odd.

I know he has a number of pickups that don't work with other types. I think the reason is half of the pickup would be out of phase. I figured he was doing a split coil setup, but with the same magnetic polarity on both halves.

Do you have a compass you can pass over parts of the pickup to see the magnetic polarity?

You can also try this:



[yeah, I've used this picture before... but it's still funny to me]

"If you're captured, you may want to take your own life. Use this."

[tubby.twins]

That's pretty funny.

[Joe Gwinn]

I've never seen that circular pattern in the magnetic paper before, and I've tested quite a number of bass humbuckers. ....

And by the way, the pickup sounds just fine. I was just puzzled by what I saw, so I thought I'd ask the forum. Any ideas?

Magnetic paper actually shows the gradient of the magnetic field, not the absolute value of the field. Think about some well-separated small iron spheres in a totally uniform magnetic field. Do the spheres experience any forces? If no forces, there will not be any image seen in the paper.

[Joe Gwinn]

And I thought of another effect: One can saturate the magnetic particles in the magnetic paper, and if anything can do this it will be a neo magnet. The permeability of saturated particles will drop to approximate that of air. So, the particles in the high-field area will be essentially non-magnetic, explaining the empty center (ring versus disk). The test is to move the paper away from the pickup under test, and see if the circle fills in.