Dropping permeability of (1018?) fillister head 'bucker type pole screws

[jop120]

I was playing around with pole pieces recently, originally trying to use High-tensile steel screws. one thing I noticed is that a steel pole piece with lower magnetic permeability will have more of a low cut effect with harsh highs, more than a lower output overall. So if it's the treble strings that you're trying to reduce then that might not work as desired.

How about trying to de-gauss the magnet a little around the problem area? don't know if it'd work, but could be worth a try.

[zparts]

I was playing around with pole pieces recently, originally trying to use High-tensile steel screws. one thing I noticed is that a steel pole piece with lower magnetic permeability will have more of a low cut effect with harsh highs, more than a lower output overall. So if it's the treble strings that you're trying to reduce then that might not work as desired.

How about trying to de-gauss the magnet a little around the problem area? don't know if it'd work, but could be worth a try.

Do you have a keeper bar around the polepieces? If so try cutting the keeper bar shorter off of the 2 polepeieces that are the problem, leaving it around the others. Then fill the gap between the magnet and those poles with a non-ferrous material like plastic or wood.

[Antigua]

This seems like a strange objective, because reducing the permeability reduces the effectiveness of the screw pole piece in general. Suppose you're doing this to reduce the inductance, you will also decrease the coupling between the coil and the guitar string, which reduces the voltage output, so you could have just as soon put less turns of wire on the coil.

[Helmholtz]

I understood that the OP wants to reduce the signal of a couple of individual strings only.

[David King]

I'd make a few more identical coils and see if they all suffer from the same idiosyncrasies first.

I'd look long and hard at the string choices and see how much flexibility the player has to adapt to some other choices. There are always better strings out there for the choosing but if a player is locked into a brand then perhaps contacting that brand's tech support person might unlock some further refinements. In my experience the larger the brand the more focused they are on maximizing profits but the more resources they have available to fix problems.

From the description Fieldwrangler has given I'm imagining something akin to an Erno Zwaan Q-tuner pickup.

[fieldwrangler]

Folks -

This business of string outputs is indeed hairy. With flatwounds, especially, there seem to be numerous ways to skin numerous cats in terms of core diameters, wrap thicknesses and even double wraps.

One thing I'm glad about regarding this thread is this timbral difference that Helmholtz has brought up. This is quite interesting, I think, and I look forward to doing some listening around here within the next week or so.

[Antigua]

You mentioned acquiring higher carbon screws and hoping they look the same, but supposing you can get some identical electrical steel screws to experiment with, you could use a dremel with a grinding stone, and then gouge sections out of the side of the screw shaft. So long as the bobbin (or whatever) these screw into is longer than the gouges, it should still work like a normal screw, with portions of its own threading missing. I think you just have to be careful not to remove so much steel that it causes the screw to easily bend in half.

[Diablo]

You can reduce the permeability of the screw by changing the microstructure of the steel. Large grains with a fully annealed and softened structure will have the highest permeability. Any cold work lowers the perm. If you were to austenitize and quench the screw in water, you will greatly reduce the perm by converting it to martensite. Heat the screw to around 1680F and drop in water.

[salvarsan]

Impractical suggestion:
Stainless steel type 400? (410,416,430) have relative permeabilities about 20% lower than 1018 steel.
I can only find hex head screws, no fillister heads.

[Helmholtz]

Stainless steel type 400? (410,416,430) have relative permeabilities about 20% lower than 1018 steel.

Do you have reliable data on initial permeabilities of different steel types?
I am especially interested in low carbon steel like 1006, 1008, 1010.

[Diablo]

Do you have reliable data on initial permeabilities of different steel types?
I am especially interested in low carbon steel like 1006, 1008, 1010.

The permeability of 1006 to 1010 could range from 500 to 3000, depending on the %cold work, the microstructure, and the crystallographic orientation of the grains. An annealed structure will have higher perm. Steel that is physically soft is also magnetically soft.

[Antigua]

I bought some various steel pole pieces from Addiction FX and plotted them in a test coil. The plot lines all overlapped, meaning the inductance was effectively identical for each.



I don't know if any of these grades are 20% greater or lesser in terms of inductance, but because the reluctance path is mostly air, the effect of permeability is limited. For example, even though steel is over 100 times as permeable as AlNiCo, the difference in inductance between steel and AlNiCo pole pieces is only about double.

[Mike Sulzer]

Pole piece materials differs in both permeability and conductivity. As HelmHoltx pointed out, changes in permeability (as long as the relative permeability is greater than a few times) have little effect in an open magnetic circuit. So sonic differences from pole piece material (if they really stand up to double blind listening tests) would be expected to be from the conductivity.

Changing the length of a pole piece seems like the easiest way to make changes in output, but this does require experimentation.

[Helmholtz]

The permeability of 1006 to 1010 could range from 500 to 3000

Thanks.
Are these µi (B-->0) values?

I am actually looking for a µi table where I can see the (relative) differencies between different steel types. Also looking for specific conductivity values.

[Diablo]

Thanks.
Are these µi (B-->0) values?

I am actually looking for a µi table where I can see the (relative) differencies between different steel types. Also looking for specific conductivity values.

No, those measurements are for 1.5 Tesla / 60Hz. You won’t ever find relative permeability numbers for different types of steel because the permeability is too dependent on the microstructure of each type of steel and that depends on the thermomechanical processing. The same piece of 1006 steel could have a perm of 500 up to 3000, depending on the processing.

In general, as the purity of the iron increases, the permeability increases at 1.5 Tesla.

Conductivity is more straightforward, and depends mainly on the amount of solid solution alloys. There won’t be a lot of difference in plain carbon steels used for magnetic applications. Carbon won’t have a big influence. However, stainless steels have around 12% Cr + Ni etc., so will have larger resistance (electrical and thermal).