Capacitance raising potting solutions/dielectric effect....

[Possum]

I've been experimenting with raising a coil's capacitance with different liquids. I've noticed that some claim shellac will raise capacitance and on the chart of dielectric ratings its higher than wax and theoretically ought to work. I know some pickup makers claim it makes coils sound "vintage," but in my own experience I think its being misinterpreted because it an alcohol borne solution and there is water in commercial mixes. It does change the tone, but several weeks later the effect is gone, because the water is probably finally evaporated. I also tried castor oil which has a high rating, but it doesn't penetrate hardly at all because its very thick, and taping the coil becomes near impossible. I once rewound a coil from a bass guitar that was totally soaked in some kind of goopy fluid all the way through, so maybe this isn't a new idea. Telsa coil makers submerge their coils in mineral oil and it raises the coil capacitance some, but again, messy stuff. I wonder if anyone has experimented with this or has other ideas. Acrylic compounds are out because they are water borne products also. I used to pot in with shellac because it was quick and I liked how it worked but never never really heard any tone change until my jar had soaked up water from the air and the coils would never dry, so abandoned it. Anyway, this ought to make an interesting thread....

[Possum]

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No one has experimented with this????

[Joe Gwinn]

If we told you we would have to kill your tone.

[David Schwab]

I used to pot in with shellac because it was quick and I liked how it worked but never never really heard any tone change until my jar had soaked up water from the air and the coils would never dry, so abandoned it. Anyway, this ought to make an interesting thread....

You have to work from fresh flakes, and make up small batches.

[Possum]

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Corn flakes? I was going to take a second shot at it using flake and water free alcohol, or water free shellac solvent. I wonder if the darker flake is more dense than the lighter stuff....

[Possum]

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I did some research, shellac is a resin made by bugs, I didn't know that, cool. I wonder if there is another resin with a higher dieletric rating more towards what water is that would work, something that could be thinned enough to penetrate into coils. Guess this calls for alot of experiments. Since the darker grades are much slower to dissolve I assume they are more dense.

[KGWagner]

Electrically speaking, capacitance has to do with proximity of conductors more than anything else. So, changing dielectrics is more an exercise in changing the separation between conductors and finding a practical breakover voltage (dielectric strength, or insulation rating). Since the voltage in a pickup is incredibly low, dielectric strength isn't usually an issue. Air works. Also, since you're talking about potting, the distance between conductors is essentially already set by the tightness of the winding and the thickness of the wire's insulation.

I've heard a half dozen different reasons for potting pickups, but the only one that really makes sense is the mechanical integrity it brings. Everything gets held in place in the face of a lot mechanical stress from vibration and impact, so the thing stays consistent and lasts longer. Wax works well because at higher temperatures than it'll ever encounter in use, it's a fairly thin liquid. Put the pickup in a vacuum, fill the vacuum with hot wax, and it gets permeated. After it's cool and the wax hardens, it's a pretty solid little rascal, ready for the tender ministrations of a Stevie Ray Vaughn <grin>

[Possum]

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All true. There has got to be a way to do this though, just introducing water into a coil makes a radical difference in the tone, much water at all and they go really dull and dark, so there should be some substance that's stable that could mimic a slight bit of moisture in a coil. I don't really want to pot the coil and I don't see this at all as wanting to soak the whole coil, just some outer layers enough to tame bright wire. This is part of the bitch of trying to reproduce accurately a real PAF, all the materials made now vs. then are real clean and technically superiorly made, magnet wire, steel, and magnets are all "better" than what was made in those years. You want those tones you have to figure out how to crap it up some

[David King]

There is a water based shellac now. In fact there are all kinds of waterborne finishes these days. That moisture will eventually work it's way out unless you sprinkle the coil with something that's really hydrophilic like salt or those little crystals they toss in a baggy and send in the box with your digital camera.

[Magnut]

How about Tru-Oil? It's thin, it will harden (dry), and it can be tinted. Just don't know if there are any issues of it stripping off the existing insulation.

Oh and it's quite inexpensive, found at gun shops and some hardware stores.

[Bruce Johnson]

I pot my pickups with Smith's MultiWoodPrime epoxy. It's a special epoxy made for soaking into wood as a preparation for finishing. Its viscosity is about like water or less. Dribbled or brushed onto the coils, it immediately soaks all the way in to the bobbin. It dries in about 4 hours, and it doesn't get rock hard. The coil is still slightly squishy, even after a few weeks. It seems to glue all of the wires together pretty well.

I haven't seen any significant change in resistance before and after potting, so I presume that it isn't hurting the insulation. I can't say if it changes the capacitance, or how it changes the tone in comparison to some other potting method. I tried it out when I was first developing my pickups, and it worked well, so I've stayed with it.

Warning: the fumes from it while mixed and curing will knock you over. Ventilation is required!

[Possum]

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OIls are usually no higher dielectric rating than potting wax, might be bad for the insulation too maybe. I don't think the water based stuff is a good idea, and besides, again, acrylic resins aren't much more than potting wax, probably no discernible audio effect. Having been sent a box of Katrina victim pickups, you definitely don't want any kind of salt in there!

[David Schwab]

I did some research, shellac is a resin made by bugs, I didn't know that, cool. I wonder if there is another resin with a higher dieletric rating more towards what water is that would work, something that could be thinned enough to penetrate into coils. Guess this calls for alot of experiments. Since the darker grades are much slower to dissolve I assume they are more dense.

Yes, the Lac bug. So was lacquer before the invention of nitrocellulose.

I do believe the darker shades are denser.

Yeah, potting is just to keep things from vibrating. I've been having good results with varnish.

We talked about this a while back... there are "magnetic" paints that have a lot of iron (or some other metal) particles in it. You are supposed to spray them on a surface so you can stick magnets to it. And there are also those shielding paints. If you are trying to knock some high end off the pickup, I bet one of those might work.

[Possum]

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The desire is to mimic vintage magnet wire. Just coating metal on the outside, you can wrap with copper tape and ground it, but you don't get the same effect, and it sucks the life out of it too, been there done that one, I didn't like how it sounded. Do you notice any high end damping with varnish?

[David Schwab]

Oh I see.

No, the varnish sounds the same to me. The pickups in my test bass aren't potted at all, so I used that bass as a control when testing pickups.

I've also tried polyurethane and super glue, and I don't hear any change with those either.