Strings passing right thru the coil

[madzub]

I feel like I saw an example of this once, but can't find anything on it. Has anyone tried a pickup in which the strings go right through the coil? Not just thru a magnetic enclosure as on the valco lap steel pickups and similar, but right thru the coil, in other words, the coil wrapping around the strings? So, the strings would literally be the core of the inductor...

I'm going to try this with an X2N pickup, by removing the bar, which leaves a bobbin form with a 3/16" gap. Any idea how it's going to sound? Huge output, or nothing special?

[Helmholtz]

The principle of magnetic PUs is based on magnetic induction.
Means that a signal voltage is produced by a changing magnetic flux through the coil.

Just passing the strings through the coil will not produce a signal as there is no changing flux.

[madzub]

A magnet would be used to magnetize the strings, of course. Hence there would be loads of changing flux in the core, no?

[Helmholtz]

A magnet would be used to magnetize the strings, of course. Hence there would be loads of changing flux in the core, no?

The total flux through the coil (and perpendicular to the plane of the coil) must be changing.

The vibration of a magnetized.string will not cause a significant change of total effective flux through the coil.

For further analysis I would need to see the complete arrangement with the magnet.

[madzub]

I think I'm understanding.... So even though the core is moving, so long as its amount of magnetization (in plain-speak) stays the same, it won't produce a signal.

I've read that most of the signal of a regular pickup is generated by the up-down motion of the string, in other words, the string moving towards and away from the core, hence a changing amount of flux with varying distance.

But in my idea, the strings would still be moving toward and away from a magnet mounted nearby, so there should still be changing flux within the coil. And with the strings going thru the coil, I think of that as if the string is really really really close to the polepiece, hence a potentially very strong signal.

But, since there won't be very much metal in the core, it would not have much inductance, so perhaps a stronger signal would be had by using a big metal core (such as the X2N's big rail) with the string outside as in a regular pickup arrangement.

[Helmholtz]

But in my idea, the strings would still be moving toward and away from a magnet mounted nearby, so there should still be changing flux within the coil. And with the strings going thru the coil, I think of that as if the string is really really really close to the polepiece, hence a potentially very strong signal.

Don't forget that the orientation of the flux matters.
Only the (changing) flux component perpendicular to the coil (i.e. along the strings in your case) can produce a signal.

Please show a drawing.

[tedmich]

maybe through the magnet, not coil?

[madzub]

Well, I tested the idea, and it worked... Even without a magnet anywhere, it produced a sound of reasonable volume and very clear tonality.

And with a magnet held close by, it got loud, real loud. Didn't seem to matter how the magnet was oriented. Even when held several inches away, the volume increased, and held anywhere close it got very loud.

Compared it to the other regular coil held above the string, and it was also loud, as it's an X2N after all.... So I can't say how amplitudes compare from this simple test, but they're are least somewhat comparable.

Interestingly, with no magnet, the volume changed as I moved the coil around, so it seemed to matter exactly where within the coil the string sat.

[Helmholtz]

Experiment beats simple theory (doesn't mean that theory is wrong).

Seems your strings are already permanently magnetized and you have a second-order effect caused by asymmetries/inhomogeneities.

[madzub]

Experiment beats simple theory (doesn't mean that theory is wrong).

Seems your strings are already permanently magnetized and you have a second-order effect caused by asymmetries/inhomogeneities.

Actually that bass has not had pickups in it since those strings were installed, so I don't think they're holding a magnetic charge. Maybe it's a stray EMF from the wiring in this old house? Or there's a tiny bit of current coming from the amp causing an EMF in the coil?

[madzub]

Actually that bass has not had pickups in it since those strings were installed, so I don't think they're holding a magnetic charge. Maybe it's a stray EMF from the wiring in this old house? Or there's a tiny bit of current coming from the amp causing an EMF in the coil?

Come to think of it, I've probably held pickups/magnets over those strings before so perhaps they are holding a charge...

[Helmholtz]

Actually that bass has not had pickups in it since those strings were installed, so I don't think they're holding a magnetic charge. Maybe it's a stray EMF from the wiring in this old house? Or there's a tiny bit of current coming from the amp causing an EMF in the coil?

I couldn't work without any residual string magnetism.

AC fields rather de-magnetize than magnetize. And would produce a hum signal in your coil.

I could measure some tiny flux density even with new guitar strings. It varies along the length of the string and is not a reliable property.

[bbsailor]

I feel like I saw an example of this once, but can't find anything on it. Has anyone tried a pickup in which the strings go right through the coil? Not just thru a magnetic enclosure as on the valco lap steel pickups and similar, but right thru the coil, in other words, the coil wrapping around the strings? So, the strings would literally be the core of the inductor...

I'm going to try this with an X2N pickup, by removing the bar, which leaves a bobbin form with a 3/16" gap. Any idea how it's going to sound? Huge output, or nothing special?

I always like tinkering with new ideas just to learn how my experiments measure up against the theory.

Here are a few things to try.

1. Magnetic field effect on string damping, output level and tonal chance. Try these experiments.
a. Single magnet
b. Up and down dual magnets over and under the string
c. Ring magnet, single
d. Dual ring magnets one in front of the coil and one behind the coil.

2. Bass strings are sensitive to pole placement related to degree of harmonic output. Dual magnet poles for a string put the string in a gap area and when it vibrates it will emphasize the second harmonic when it vibrates between the poles. Spacing of the magnets relative to string diameter and pickup location between neck and bridge will affect the amount of this effect.

Keep us updated on your findings.

Joseph J. Rogowski

[madzub]

2. Bass strings are sensitive to pole placement related to degree of harmonic output. Dual magnet poles for a string put the string in a gap area and when it vibrates it will emphasize the second harmonic when it vibrates between the poles. Spacing of the magnets relative to string diameter and pickup location between neck and bridge will affect the amount of this effect.

Yes, I had given this concept a lot of thought and was just reading up about it. That arrangement of 2 poles with a gap below the string will sense a lot of the side to side motion of the string, which creates a 2f signal, ie an octave above the fundamental, since the string enters and exits the dense flux area (plain speakin') twice for every vibration. Also this design apparently has a smoother attack on the note.

Whereas a blade essentially registers no change in flux from side to side motion, only up and down, which is probably why blade pickups like the X2N and Lawrence L500xl can be very high output but still have clarity, since they don't have that extra 2f stuff added in.

Has anyone tested the Duncan parallel axis design? It should really emphasize the 2f effect, and in fact, with enough string motion, such as in the neck position on a bass, should produce 4f content as the string enters and exits high flux zones 4 times for every revolution.

I wasn't planning to use the thru-coil idea in a bass, I just had the bass lying around, convenient for testing the concept. The string motion would be too wide for that gap in practice, so a much larger coil would be needed. I was actually searching for a very sensitive pickup for a touch guitar (ala chapman stick) which has very little string movement. Another topic to explore is what sort of flux design would be best for this type of instrument: one that emphasizes up-down motion like a blade design for sharp attack and clarity, or the gap design that softens attack and gives a more coloured tone with the added harmonics?

I'll try to set up a more solid test bed and try different magnet arrangements. Regarding the ring magnet, Joseph, what polar arrangment were you thinking of? They can be axially, diametrically, and rarely radially magnetized.

[bbsailor]

Yes, I had given this concept a lot of thought and was just reading up about it. That arrangement of 2 poles with a gap below the string will sense a lot of the side to side motion of the string, which creates a 2f signal, ie an octave above the fundamental, since the string enters and exits the dense flux area (plain speakin') twice for every vibration. Also this design apparently has a smoother attack on the note.

Whereas a blade essentially registers no change in flux from side to side motion, only up and down, which is probably why blade pickups like the X2N and Lawrence L500xl can be very high output but still have clarity, since they don't have that extra 2f stuff added in.

Has anyone tested the Duncan parallel axis design? It should really emphasize the 2f effect, and in fact, with enough string motion, such as in the neck position on a bass, should produce 4f content as the string enters and exits high flux zones 4 times for every revolution.

I wasn't planning to use the thru-coil idea in a bass, I just had the bass lying around, convenient for testing the concept. The string motion would be too wide for that gap in practice, so a much larger coil would be needed. I was actually searching for a very sensitive pickup for a touch guitar (ala chapman stick) which has very little string movement. Another topic to explore is what sort of flux design would be best for this type of instrument: one that emphasizes up-down motion like a blade design for sharp attack and clarity, or the gap design that softens attack and gives a more coloured tone with the added harmonics?

I'll try to set up a more solid test bed and try different magnet arrangements. Regarding the ring magnet, Joseph, what polar arrangment were you thinking of? They can be axially, diametrically, and rarely radially magnetized.

I would obtain two magnets of each type you can find. The inside magnet diameter should match the coil inside height or be just a little larger. The location along the string will determine how wide the string vibration would be where it might hit the magnets. You should measure with each magnet type:
1. Output voltage
2. String damping vibration time
3. Tonal changes or harmonic changes
4. Noise pickup

Keep experimenting!

Joseph J. Rogowski