Magnetic Pickup Wire Insulation Notes

[morange]

I've recently considered these three wire insulation materials:

Plain Enamel
Solderable Polyurethane (Electrisola P155, NEMA MW 79-C)
Solderable Polyurethane w/ Nylon Overcoat (Electrisola PN155, NEMA MW 80-C)

I don't want to use Plain Enamel, because it's too expensive, and I'm concerned about the durability of the insulation as it ages. I've chosen the Polyurethane over the Polyurethane w/ Nylon Overcoat, and here's why.

I've concluded, based on extensive mind-numbing internet crawling, that the difference in sound when using different wire insulation materials (using the same wire gauge; what happens when you change wire gauge is much less mysteriously discussed online) can be understood as differences in capacitance. I found this page on the factors affecting capacitance helpful: http://www.allaboutcircuits.com/vol_1/chpt_13/3.html

None of these differences may be audible at all; I'm assuming here that they are.

So, scatter winding puts more space in the coil than machine winding, causing less capacitance, allowing more high frequency output. That's pretty much accepted in forums. So is the idea that a thicker wire insulation (Heavy Formvar, for example) allows more high frequency output than a thin insulation. These explanations agree with the what the allaboutcircuits page says about plate spacing in capacitors.

Each insulation material has its own dielectric constant (relative permittivity); a higher value means higher capacitance, and reduced high frequency output. Here are some relevant links:
http://en.wikipedia.org/wiki/Relative_permittivity
http://202.194.4.88:8080/wulihx/data/Di ... 0Table.htm

I haven't found the dielectric constant for Plain Enamel (oleoresinous enamel), but you can sort of guess at it by looking at some of the oils and stuff in the Dielectric Constant table. You can look up the definition of oleoresin and resin - that should give some clues about Plain Enamel's composition. I've seen some online talk suggest it's similar to spar varnish, which includes boiled linseed oil. Who knows? Anyway, it seems that the dielectric constant would be pretty low, like between 2 and 4.

The dielectric properties of polyurethane and polyurethane with nylon overcoat seem close, until you consider that the nylon overcoat is hygroscopic, so it's relative permittivity will increase as it absorbs water.
http://www.elexp.com/t_wire.htm
http://www.litzwire.com/litz_film_insulations.htm

I don't intend to pot my pickups, so it seems moisture in the air will cause my pickups to slowly lose treble response if I use the poly/nylon, so I'll use polyurethane. I have seen polyurethane referred to as a hygroscopic material, online, but not by any wire companies. I don't know why that is; it could be that the polyurethane formula used for wire is not hygroscopic.

[Chuckchuck]

Can you really tell the difference? Be honest.

[morange]

I wound some tele pickups, and they do sound good, really bright and clear, especially compared to whatever the Baja Tele comes with. But that has more to do with the magnets and the tension, pattern, and number of winds, and absence of wax, I'm sure. This research was about making the best wire decision for my project based on all the information available to me. Figured someone might find it helpful.

viewtopic.php?f=192&t=35993&hilit=pickup+winding