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]

Originally Posted by 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

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]

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]

Originally Posted by 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.

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]

Originally Posted by David King

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]

Originally Posted by salvarsan

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]

Originally Posted by salvarsan

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]

Originally Posted by David King

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]

Originally Posted by Mike Sulzer

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]

Originally Posted by Mike Sulzer

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.

[Joe Gwinn]

Originally Posted by Mike Sulzer

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

How was this verification accomplished?

One would think that the ratio of volumes of neo and of steel would matter.

[Mike Sulzer]

Originally Posted by Joe Gwinn

How was this verification accomplished?

One would think that the ratio of volumes of neo and of steel would matter.

I made a small coil with a single humbucker slug as a core, put a couple thousand or so turns on it, and put a capacitor in parallel to resonate it in the audio range. Then I put various magnets on the end, and did not observe any change in the resonant frequency. I forget what the biggest neo was, but it was probably a disk 3/8" in diameter, 1/4 long. It is much easier to saturate a material when the core geometry is closed, I believe.

[Mark Hammer]

I've pondered experimenting with a pair, or even trio of blades, but the thing that tends to stymie me is the wrapping. First off, my winding apparatus demands that there be a place to stick a bolt through the middle of the bobbin into the chuck of the hand drill I use. I gather any sort of apparatus for winding around a blade/rail would require that it be held in place from two sides

The other thing is that the snugness of the wind is partly a function of the steepness of the "turnaround" at the ends of the coil. Seems to me that the further one moves away from the format the wire comes in (a round spool), the less snug the windings will be. That is, they will be tight as a drum at the ends but spongy in the middle.

So how do people get their coils to be snug when winding around a blade? Or is it simply a matter of tension and being slow and methodical?

[Dave Kerr]

I do wind more slowly with blade cores than with more traditional bobbins. As far as mounting to your drill, why not chuck up a rudimentary faceplate and use double stick tape?

[David King]

You could hold the rails to your face plate with a neodymium magnet - and check the output as you wind.

[Joe Gwinn]

Originally Posted by Mike Sulzer

I made a small coil with a single humbucker slug as a core, put a couple thousand or so turns on it, and put a capacitor in parallel to resonate it in the audio range. Then I put various magnets on the end, and did not observe any change in the resonant frequency. I forget what the biggest neo was, but it was probably a disk 3/8" in diameter, 1/4 long.

That sounds like a reasonable approach, but I would try it with a far larger neo, something on the scale of the neos used to charge alnico magnets, just to know how much margin we have.

It is much easier to saturate a material when the core geometry is closed, I believe.

True, by a goodly ratio.

[David Schwab]

Mark, I use double stick tape to secure the bobbin/rail assembly to the winder.

I do notice that if I wind fast the middle of the coil can be a little on the spongy side, but I just tape it snug with the teflon tape and when I pot it, it's nice and solid.

[Possum]

Yep you use double stick but what works best is the sorta foam type double stick stuff, I forget what its called but every 3M tape area in any grocery/hardware store sells it. Its about 1/16" thick and holds anything for winding really well. You can to be careful not to leave it there when you're done or its a bitch to get off.
I've noticed that vintage blade type pickups are wound pretty loose and I do and pot them always. A rubber band on your pulley drive helps even wraps all around the coil, Leo Fender spent years to figure that out..

[David Schwab]

Yeah, I use the 3M foam tape. I have a piece of blue masking tape on the winder's platen, which helps to remove the foam tape. I've had the foam tape pull apart bobbins, so I run my finger over it to kill to stickiness a little before I stick the bobbin on.

[Peter Naglitsch]

Jsut let me second the "do not leave the tape on for too long" statement. I have seen oven bakes finishes been ripped of steel parts when someone was trying to get the double stick tape off...

I just use simple double stick tape intemded to hold ordinary carpets in your home. But I have a bunch of different faceplates, each with a recession for made for every type of bobbin I wind, meaning I never need to move the end stop (for the wire) closest to the faceplate. Regardless if I'm winding a Tele bridge with a really thick bottom flange or a mini HB (thinnest bobbin flanges I have used this far) the coil always starts in the same plane as the faceplate top surface. The recession also means that I need less "stickyness" from the tape as the twisting motion is stopped by the walls of the recession. For rail pickups (just started to experiment with those) I have a recession and a blade set into the faceplate to hold the bobbin as the bobbins for SC sized HBs are really thin and I wouldn't trus only double stick tape to hold the bobbin in place.

[Joe Gwinn]

Originally Posted by Peter Naglitsch

But I have a bunch of different faceplates, each with a recession for made for every type of bobbin I wind, meaning I never need to move the end stop (for the wire) closest to the faceplate.

You mean "recess" (a pocket cut into the faceplate), not "recession" (a drop in economic activity, leading to reduced sales of guitars and guitar pickups).

[David Schwab]

He probably combined "recess" with "depression", making a spoonerism.

I like to take a recess every now and then, to ward off depression, especially in this recession.

[Mike Sulzer]

Originally Posted by Joe Gwinn

That sounds like a reasonable approach, but I would try it with a far larger neo, something on the scale of the neos used to charge alnico magnets, just to know how much margin we have.

The margin is already large since you cannot use magnets so large in a pickup. A humbucker with slugs in both coils and one of those magnets on each slug has very high output, but is useless as a result of the string pull.

[David Schwab]

I use magnets that measure 1" X 1/2" X 1/4" in pickups with no string pull. But that's with blades. Would probably be more of an issue with round poles.

[Peter Naglitsch]

Originally Posted by Joe Gwinn

You mean "recess" (a pocket cut into the faceplate), not "recession" (a drop in economic activity, leading to reduced sales of guitars and guitar pickups).

Jupp, recess, not recession. Probably a Freudian slip on account of the way the economy is right now...

[Joe Gwinn]

Originally Posted by Mike Sulzer

The margin is already large since you cannot use magnets so large in a pickup. A humbucker with slugs in both coils and one of those magnets on each slug has very high output, but is useless as a result of the string pull.

For guitar pickups, probably so, but bass pickups use far stronger magnets. If the margin is a percentage, it may matter. If the margin is a factor, it won't matter.