suhr and dummy coil...

[Mark Hammer]

Yes, it is possible to just guesstimate or eyeball or go for a shot in the dark. Obviously a professional touring musician who desperately needs zero hum may require the precision of trimpots to dial in optimal cancellation, but every db less of hum is a db less of hum. I'd like 0db of hum myself, but I'll happily settle for 12db less. So, yeah, you can just whip up a dummy coil that's somewhere in the ballpark and expect to hear some sort of benefit, even if it isn't as much as a Suhr system would get you.

I guess the other way to look at it is that every db less of hum makes it easier for more aggressive noise-reduction methods like noise gates or downward expanders to be set in less aggressive ways. Traditionally, we've hated noise gates as a solution because the threshold would often have to be set so high that you'dlose the initial attack of the note and lose some of the decay. If you can afford, by means of modest hum-reduction, to set the gating threshold much lower, then the noisegate's behaviour may interfere with the naturalness of the sound and instrument's dynamics much less.

[LVS]

This is an idea I had quite some time ago. I have no time to build such a thing right now, but I will soon.

Cheers,
Lucas

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[Joe Gwinn]

This is an idea I had quite some time ago. I have no time to build such a thing right now, but I will soon.

Cheers,
Lucas

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Be aware that inductance varies as the square of turnscount unless the individual coils are well separated. This is unlike the behaviour of resistors and capacitors.

[LVS]

Thanks for the answer, Joe, though it confuses me somewhat.

What I have in mind is a dummy coil like this :

- air core
- 0.2mm dia wire
- large area compared to a pickup, possibly rectangular shaped
- wound together as one coil package with several taps connected to a switch array
- connected in series with a pickup.

The switches would make it possible to dial "any" number of coil turns.

I assumed a linear relation between the number of turns and the hum field caused voltage.

The large area would involve lesser turns, making the coil inductance quadratically smaller for less impact on tone.

Is there anything I am overlooking? Influences from coil segments that are switched off?

Cheers,
Lucas

[Joe Gwinn]

Thanks for the answer, Joe, though it confuses me somewhat.

What I have in mind is a dummy coil like this :

- air core
- 0.2mm dia wire
- large area compared to a pickup, possibly rectangular shaped
- wound together as one coil package with several taps connected to a switch array
- connected in series with a pickup.

The switches would make it possible to dial "any" number of coil turns.

So far, so good.

I assumed a linear relation between the number of turns and the hum field caused voltage.

The large area would involve lesser turns, making the coil inductance quadratically smaller for less impact on tone.

For a given coil shape and size, induced voltage will be directly proportional to turns count, while inductance will vary as the square of the turns count.

The actual rule is that given a uniform hum field, the induced voltage is proportional to the area-turns product of the dummy coil. This is the area of the average turn multiplied by the number of turns.

Is there anything I am overlooking? Influences from coil segments that are switched off?

Not that jumps out at me. Open coils are invisible in this setup.

If you have a good voltmeter, you can figure out the correct number of turns. Take a dummy coil with a known number of turns and the pickup to be cancelled. Put both in the same hum field, and measure the resulting hum voltages. The objective is to make these two voltages the same.

Compute the correct turns count using the following formula:

NewDummyTurnsCount= (MeasuredPickupVoltage/MeasuredDummyVoltage)*OldDummyTurnsCount

Make a new dummy coil with the exact size and shape as the old dummy coil, but with the computed number of turns. No switch needed.

This should allow for near perfect hum cancellation.

[LVS]

Understood, thanks - it's reassuring you confirm my assumptions, which I expressed in a somewhat unstructured way. I was aware of the Area-Turns product : I was gonna start from an estimation of Area x Turns of a P-90 to apply to the dummy, and then increase the dummy's calculated number of turns to a number satisfying that powers-of-2 formula.

The method you describe to use voltage ratio to build a new coil is more simple, I must admit.

This er, "binary" dummy coil idea is actually a spinoff of a few guitar pickups I made in the same manner. I'm gonna give it a go anyway. For the experience, and as a tryout alternative to Mr. Suhr's pot-adjustable coil.

Cheers,
Lucas

[Dave Kerr]

How about the gauge of the wire in the dummy coil? For a given area and turn count, what would the effect be on the induced voltage by substituting 37 AWG wire (.0068" dia) for 43 AWG (.0036)? Assume that the size of the coil is rather large, so the increased thickness of the wire doesn't contribute appreciably to the outside diameter of the coil.

[Joe Gwinn]

How about the gauge of the wire in the dummy coil? For a given area and turn count, what would the effect be on the induced voltage by substituting 37 AWG wire (.0068" dia) for 43 AWG (.0036)? Assume that the size of the coil is rather large, so the increased thickness of the wire doesn't contribute appreciably to the outside diameter of the coil.

Won't make the slightest difference, and #37 is far easier to handle.

[Thorny]

I had a Kramer Classic (their answer to a 62 reissue at that time - mid-to-late 80s). It had three duncan alnico single coils with a 4th reverse wound one mounted inside the cavity but underneath the pickguard. It was used to noise cancel the 3 pickup that were mounted normally. It worked well, but took a little bit of the top end off of the pickup in my opinion. But I do think it worked better than most solutions or humbucking replacements.