Rail Pickups

[guitarcam123]

What are the rails actually made from?

I have a some aluminum that I could cut up, but is it suitable for the rails?

[Possum]

...

No aluminum is non-magnetic, you need steel. I read that Joe Barden found the ideal steel in road signs he would steal of the highway. I think some also use magnetic stainless steel....

[salvarsan]

Yah, like Possum said.

You need magnetic rails to carry the magnetism to the guitar strings.

16 gauge steel is a good place to start.
The technical specs for low-carbon steel are AISI 1005 to 1018.

Scrap silicon steel from transformer cores, and Mu metal shielding
from CRT displays are both excellent magnetic conductors.

Generally, cheaper is better.

-drh

[bbsailor]

Yah, like Possum said.

You need magnetic rails to carry the magnetism to the guitar strings.

16 gauge steel is a good place to start.
The technical specs for low-carbon steel are AISI 1005 to 1018.

Scrap silicon steel from transformer cores, and Mu metal shielding
from CRT displays are both excellent magnetic conductors.

Generally, cheaper is better.

-drh

For some good shielding, check out this link.
SALE! Rare Ultraperm 80 Shielding Sheet-The Electronic Goldmine

This shielding can be cut to form a laminated core.

Joseph Rogowski

[Mike Sulzer]

Saturation

Has anyone using high permeability material as pickup cores checked to see ifthe material saturates?

[Possum]

....

I've used an electrical iron thats optimized 1002 alloy. Its used in tape recorder heads, I don't know if thats what you mean, but sounded real good, way too expensive to grind to size and shape so I quit plus it wasn't a big hit with customers.....

[Joe Gwinn]

Note that the high-permeability nickel alloys are very sensitive to mechanical strain. For instance, it is customary to hydrogen anneal mumetal shields after fabrication for this reason.

Also, beware magnetic saturation, as Mike mentions.

The good news is that in general the alloys with higher saturation levels are less sensitive mechanically.

I do recall that there were some pickups with mumetal components, and some high-grade audio microphone transformers use laminated mumetal cores.

[David King]

Any practical advice working with this stuff? I can't imagine that 80% nickel alloy will treat your mom's sewing scissors very well.

What happens when a core saturates in a passive pickup? Does it act like a square wave generator or a soft knee compressor? Could that be a good thing sound-wise?

I'd think a good use for a thin foil would be to shield the dummy coil in a stacked pickup design from the upper coil's magnetic field. Has anyone here tried that?

[salvarsan]

Any practical advice working with this stuff? I can't imagine that 80% nickel alloy will treat your mom's sewing scissors very well.

It tends to be "gummy" as alloys go.

I'd think a good use for a thin foil would be to shield the dummy coil in a stacked pickup design from the upper coil's magnetic field. Has anyone here tried that?

Both Kinman and Dimarzio's Virtual Vintages use partial shielding on the lower coil.

-drh

[David Schwab]

What happens when a core saturates in a passive pickup?

I'd like to know the answer to this as well.

I see that in the patent for the SCN pickup (7227076), Bill Lawrence started that he used "moderator bars" to minimize saturation of the cores.

I use some very strong magnets with steel blades, and I can't imagine that I'm not saturating them. From my experiments, swapping out the neos for ceramic magnets gives a thinner tone.

[David Schwab]

Generally, cheaper is better.

My first pickups back in the 80's used some plain cold rolled steel bar that I got from a steel shelving unit. Later I bought steel bar stock from Home Depot.

They all seem to work well.

[David Schwab]

Both Kinman and Dimarzio's Virtual Vintages use partial shielding on the lower coil.

The newer DiMarzio designs only have the shield on the top coil. Between that and adding steel slugs to the bottom coil, it looks like they want to make it as sensitive to noise as possible.

[Mike Sulzer]

What happens when a core saturates in a passive pickup?

Saturation of the core does not cause non-linearity in the response to the vibrating string. Saturation means that the magnetic material has been magnetized as much as it can, but he field from the vibrating string is very small, and so it does not move the core out of saturation.

A saturated core does not have a permeability very much higher than a non-ferromagnetic material. Thus the inductance could be two or three times lower than you would expect, and the output level of the pickup might be several times lower than you would expect. A material that saturates at a very low level might not be able to transfer a strong enough magnetic field to the string.

I use a ferrite material that has an initial permeability a few times that of steel. There is a limit to how large a field one can achieve at the string when using a magnet on the bottom (although it might be just enough in some cases). That is why I use very small neo magnets on top. With neo available, I do not see any reason to use magnets on the bottom rather than the top when using a core material with a high permeability.

I have verified that even very strong neos on the bottom of steel slugs do not cause the steel to saturate.

[David Schwab]

I have verified that even very strong neos on the bottom of steel slugs do not cause the steel to saturate.

Well that's good to know.

[Joe Gwinn]

A saturated core does not have a permeability very much higher than a non-ferromagnetic material. Thus the inductance could be two or three times lower than you would expect, and the output level of the pickup might be several times lower than you would expect. A material that saturates at a very low level might not be able to transfer a strong enough magnetic field to the string.

Another consequence of saturation is that the permeability of the saturated material drops from ~2,000 to ~2 and the saturated material no longer focuses the magnetic flux, so leakage flux goes way up. Whether this is a good thing or a bad thing will depend on the pickup design and design intent.