micro PU question

[tedmich]

howdy learned ones!

I am pulling together an odd project and need to finalize some very small pickups which will be implanted in very small and inaccessible places; under the 12th fret and near the nut! The design I've settled on has fixed pole pieces and a coil/magnet assembly which will slide in from the top of the neck, where wiring can be dealt with.

The pole pieces are my current question. Having read some previous discussions regarding the (lack of) utility of tiny N45 type magnets as pole pieces I have a couple of choices for the metal I'll use.

A 1018 steel (~98% Fe)
B 99% pure nickel
C 55% nickel/ 45% Fe

any preferences? Why? These will be 3/32" rods implanted 0.125" from Jescar SS frets (at fret 12) and a Graphtec black nut. The nickel rods are std welding electrodes from McMaster Carr and very cheap at $0.08/in.

So base question: which pole piece metal?

Background:
These frets will be used to amplify palindromic notes upstream of the fretted note, or between two fretted notes. This would work better with a frettless design but I am going to try it first with a fretted one. I had thought of using the Jescar fret as a pole piece, but figured this would be weak and difficult to fabricate. I am a bit nutty.

[David King]

This seems like a much better job for contact piezo pickups.

[tedmich]

how close do I need to get with a Piezo? No "contact" is possible at the 12th fret, maybe at the nut... I believe Zappa had a guitar with a peghead piezo but I want real notes. Any preference on the metals?

Dave I used my memory of one of your nice fretless basses (that I checked out a few years back at Marylhurst) for the thought experiment on this. With high enough action and neck bow you will get 3 notes from 2 fingers. With frets (or maybe conductive fret lines) you could even do auto switching between the 3 pickups and their upstream/midstream/downstream notes. Could be pretty neat.

Realistically I could "come over the top" at the nut without too much problem, its the 12th fret unit I need "underground"

[defaced]

I don't think either of the nickel based electrodes are good choices given my limited understanding of pickup operation physics.
99% Nickel will be a purely austenitic structure, it is not magnetic.
Given that Fe does not appear in the Cr/Ni equivalents of the Scheaffler Diagram (or the WRC 1992 diagram), and Ni is off the charts at 55%, my guess is the 55% Ni - 45% Fe will be completely austenitic as well.
Further, welding electrodes are not precise products in terms of dimensions. A 3/32 stick electrode will likely not be 0.188in in diameter.

[tedmich]

1018 steel is your vote, eh Mike? that's cheap and easy! These will be slugs flush with back of fretboard and need not be precise.

the magnetic permeability of Ni55/Fe45 should be quite healthy, likely somewhere between 45 permalloy and 78.5 permalloy

from http://www.alcatel-lucent.com/bstj/v...stj2-3-101.pdf

see also
http://www.alcatel-lucent.com/bstj/v...tj15-1-113.pdf

[defaced]

Not a recommendation in the slightest as I've never wound a pickup in my life (and don't intend to), but I do have some idea of what the microstructre of the alloys you mention are. Given the price, you could try all three.

[tedmich]

Salvarsan stated:

"Poles and blades are commonly made of soft (= low carbon) steel like 1010 or 1018, depending upon builder preference. Mu metals and similar, while superb magnetic conductors up to a point, saturate at a lower field than cheep steel and actually pass _less_ magnetic field for a given magnet."

while I am unclear on the veracity of this statement, I'll try the cheap stuff as well!

[salvarsan]

Salvarasan stated:
"Poles and blades are commonly made of soft (= low carbon) steel like 1010 or 1018, depending upon builder preference. Mu metals and similar, while superb magnetic conductors up to a point, saturate at a lower field than cheep steel and actually pass _less_ magnetic field for a given magnet."

while I am unclear on the veracity of this statement, I'll try the cheap stuff as well!

Study the actual permeability curves of your materials.
Concepts: BH curve, saturation

[madzub]

Fred Frith uses a regular pickup suspended over the strings by the nut... that would be a simpler solution.

I can't quite picture the pickup design you're describing. but i've thought about putting pickups in these places before, and i think something like the alumitone design would work well, as the primary loop can be made very thin, and the secondary could hang out over the side of the neck. In fact you could make the primary out of copper wire or sheet, make it a bit wider than the alimitone design but slightly thinner than the height of the frets, use thin magnets, and you could install it right on the fingerboard without cutting into it at all. if you have to cut much meat out of the fingerboard/neck then you're compromise its strength.

Your idea of picking up the "palindromic" notes would work better with a slide/steel, as it would function like a "middle bridge" or "3rd bridge", look them up if you haven't. That way the 2 notes on either side of the slide would be harmonically related; with standard frets they won't be so neatly harmonic.

[tedmich]

I am looking for complexity over simple harmonic relationships, the three notes/two fingers idea will work better on a fretless but finger dampening means I'll need either a brass fretboard, sustainer or non-dampening finger prosthesis to get this to work with guitar strings. I'll deal with high action but slide is a dead end for me; unless I can use ten of them!

I'll go with my 49AWG N40 based 1018 pole piece design and see what I can get under the fretboard; the neck is plenty stout, Madagascar ebony and flame hard rock maple (28mm at the 12th fret) 24" SS dual action truss rod and 2 CF spars (3mmx10mm) the entire length.

Saw Fred Frith at Reed College many years ago, he was a hoot!

[rjb]

...finger dampening... non-dampening finger prosthesis... slide is a dead end for me; unless I can use ten of them!

Thimbles.

[Kindly Killer]

I wonder if someone wouldn't mind filling me on what the pickup at the nut does? I know the effect of fretwraps - taking away all the garbage south of the fretting hand - but i'm trying to imagine what you would get by amplifying the strings down there.

?

[tedmich]

I am going to use 1008 steel which is min 99.21% pure Fe


more notes is the goal, I'll only be able to learn to use them once they're possible!

[David King]

Saw Fred Frith at Reed College many years ago, he was a hoot!

He was a hoot, I believe he was also drunk as a skunk. Fun show for sure.

[tedmich]

David, you are an old time PDX'r! Michael Hedges (in PDX around the same time) was totally blitzed on weed every time I saw him. I tend to think the drugs don't help the creativity, but its hard, at times, to separate the two.