Brian May boost info fer you.

[Bluesgeetar]

Just read a guitar magazine, can't remember the name.  Was a special issue named Legends or Guitar Legends or something.  Anyway had tons and tons of info provided by Brian May.
Here is a statement Brian made in an interview about the treble booster:  "The boost is modeled after a Rangemaster.  It is a one-stage germanium capacitor-coupled preamp."  Also Brian insists over and over that his signature tone is from the pickups on his guitar being out of phase.  In series out of phase.

Update:  It's in Guitar Worlds "Guitar Legends"  a special edition of Guitar World mag I guess.

[Fret Wire]

When you look at it from a common sense point of view, potting materials are of no consequence. Potting came about because back in the day, they didn't have pickup winding machines as precise as they do now. So many times, the windings would have loose spots that could rub under vibration and cause the pickup to be microphonic (squeal). So the potting solidifies the windings so they don't move. Many modern pickups are wound so perfectly, tension wise, they aren't microphonic anyways. Of course the old scatter wound pickups have a character all their own, but that's another story.

Potting material is an inert, non-conductive material, that solidifies pickup coil windings. Normal potting materials are parifin/beeswax, epoxy, and the various "secret recipies". I use parafin/beeswax, with great results. As long as the potting material doesn't melt or shift under normal use, holds the windings tight, and does not become hydroscopic, it's doing it's job.

As far as the expert pickup manufacturer's claiming otherwise, well... they also know the value of "mojo" advertising. Most people's quest for great tone can be easily led by mojo and they capitalize on it. The replacement pickup market is only so big, and those guys can only go on and on so much about magnet types and number of windings. They all need to have a special claim that sets them apart from the others.

Your Wagner's sound good because of the specific Alnico magnet type he uses, the magnet strength, and number of windings of a specific gauge wire that Wagner found all work together in harmony to make a great sounding pickup. I don't believe an inert, non-conductive compound holding the coils together has much to do with it.

[R.G.]

There is one other thing that potting compounds do for/to you: they change the self capacitance of the winding, sometimes significantly.

The capacitance of any capacitor is determined by the size and spacing of the two electrode plates and what the insulating gap is filled with. Air and vacuum have a capacitive multiplier constant of very close to 1. Other materials are larger.

Aluminum oxide and tantalum oxide are two such materials. By using their oxides as the entire insulating surface, the capacitance of electrolytic caps is from two to ten times greater than it would otherwise be based on electrode area.

In a coil, the turns either touch, and the capacitive multiplier is whatever the wire insulation has, or they have air between them, multiplier of 1. If you pot the coil, the capacitance increases because you fill all those air voids with gook that has a capacitive multiplier greater than one.

This typically decreases the self resonant frequency of the coil. It's repeatedly measurable. It's a know effect in tube output transformers, but guitar pickups have the sensitivity too.

[Bluesgeetar]

R.G.,  sometimes you amaze me dude.  Thanks for that bit of knowledge.  I actually did a cut and paste on that one.  really thanks for that one!

Another interesting fact I dug up somewhere about Gibson is that for a very short period back in the 50s they did try potting their humbuckers with some type of resin.  It was for a very very short time.  I can't remember why they stopped.  I wouldn't want to make myself look stupid and try to speculate.

[Fret Wire]

In a coil, the turns either touch, and the capacitive multiplier is whatever the wire insulation has, or they have air between them, multiplier of 1. If you pot the coil, the capacitance increases because you fill all those air voids with gook that has a capacitive multiplier greater than one.

This typically decreases the self resonant frequency of the coil. It's repeatedly measurable. It's a know effect in tube output transformers, but guitar pickups have the sensitivity too.

RG, strictly speaking about guitar pickups, would you say the choice of potting material would make a real world difference you could hear? Would the increased capacitance form a hi or low pass filter on your signal? Interesting.  I've nevered measured the results of any pickups I've potted, other than noting that once they are no longer microphonic, you'll hear nuances that were being masked.

Also, if different potting materials could cause measureable differences, the use of such materials would be an inconsistant method of achieving a certain "set" capacitance. Even the modern pickup winders are going to vary in tension during the winding. Different spots of the pickup winding are going recieve different amounts of potting from one pickup to the next. Plus, potting itself is not a conisistant process. No matter how careful you are, you're never really sure that the potting agent reached every crevice. I stop shortly after there are no bubbles coming up from the pickup in the melting pot. Then I measure success by whether the pickup is microphonic anymore.

That's basically why I feel the materials used for potting will not have a repeatable effect you could reliably hear.

[Fret Wire]

For anyone who's curious what the process entails.
http://www.stewmac.com/tradesecrets/electronics/ts26fralin/ts26fralin.html

lhttp://www.projectguitar.com/tut/potting.htm

http://www.projectguitar.com/tut/dip.htm

[R.G.]

would you say the choice of potting material would make a real world difference you could hear? Would the increased capacitance form a hi or low pass filter on your signal? Interesting. ...

That's basically why I feel the materials used for potting will not have a repeatable effect you could reliably hear.

It may not be repeatable (inconsistent penetration, as you note) but it is measurable in OTs, and I'm projecting that it might in pickups, for the same reasons.

The effect should turn out as a change downward in the self-resonant frequency. If you're winding your own, you might try a self resonance test, then pot one and remeasure.

The magnitude of the change depends on the potting compound's capacitance multiplication factor. Some things are only slightly over one, some are up to the low tens.

It is possible that some other winding factor would make the self capacitance not matter very much, but off hand I can't say what would be. A test would be very welcome.

[Fret Wire]

The effect should turn out as a change downward in the self-resonant frequency. If you're winding your own, you might try a self resonance test, then pot one and remeasure.

Not that I'm closed minded, but I don't see myself using two different potting agents the next time I pot a pickup. For accuracy, wouldn't I have to pot the same pickup with different agents, measuring before the potting, and then after each different formula? Then there'd be the problem of making sure you completely removed the first potting agent before testing the second.

Kinman claims to have the best winders in the business (consistant coil spacing and tension), and vacuum pots the pickups (consistant penetration). But makes no other claims about his potting wax.

Wagner strongly advertises hand winding (inconsistant coil spacing and tension), and claims to have a secret potting agent. If he pots by dipping, the penetration will be inconsistant also. Stacked against magnet type, strength, size, wire gauge and number of windings, the potting agent just doesn't seem part of the equation other than preventing microphonics. Alot of players don't even spend enough time adjusting their pickups properly to notice a small difference.

A test would be interesting though.  All pickup makers use mojo in their advertising, a cold hard truth could save tone hunters some hard earned bucks.

[DDD]

By the way the pickup's own resonant frequency dramatically depends on it's capacity. As far as I know from my experience "external" capacity such as capacity of a cable has less effect on pickup's resonance than "internal" capacitance of a coil.
Moreover, parasitic "capacitors" inside of a coil can be spread in different ways, and this factor has a great effect on the sound, too.

[Fret Wire]

True, but we were talking about whether the capacitance of one potting agent vs another potting could be heard. I say no. Scientifically, yes, you could measure a difference. In the real world, no. Think about what I was saying earlier. Unless you have both a extremely repeatable winding method and potting method, it would not be a bankable, consistant, or reliable way of achieving a set capacitance in a pickup. The pickup manufacturers set the capacitance of the coil by number of windings, guage of wire, and wire coating. Magnets won't be perfectly consistant either.

When a manufacturer has to make claims about potting agents, they are obviously out of things to say. Ever wonder why the pickup manufacturers don't lacquer-pot them like Fender did for awhile, and boast about the vintage tone? Because there is no sound advantage, just a future repair disadvantage.

All the theory is nice, but you don't plug your guitar into an oscilloscope, you plug it into an amp, where you won't hear the differences of one potting agent to the next.