tone dulling potting....

[Steve Conner]

I don't know about magnetic paint... but how about wrapping the pickup coils in old 1/4" reel-to-reel tape instead of the usual cloth stuff? I guess VHS video tape would do too.

[Zhangliqun]

I learned the hard way that leaving a pickup in the pot too long will definitely dull the tone. As I try to get the sweet top end out of the wind pattern/technique and magnet calibration, I like to have as close to zero effect from the potting as possible so I mix the wax thin and leave the pu in the pot no more than 6-7 minutes.

But you can try different lengths of time in the pot to see where the sweet spot is. I don't know where it is exactly but let's just say 27 minutes definitely = too long.

[Joe Gwinn]

How would moisture trapped in the windings change the characteristics of the coils without ruining the entire coil?

Distilled water isn't very corrosive, especially against wire enamel or varnish, but has a dielectric constant of 80 relative to air, versus 3 or 4 for varnish and wax. Despite the high dielectric constant, it's pretty lossy as well, even if clean, so the AC resistance will go up, and the resonant frequency will drop.

Wouldn't the moisture in an unpotted coil evaporate over time?

Very slowly at room temperature, because the wire is so fine.

Leo's patent on wax potting, 4,885,970, is worth reading.

If one stored a guitar in a cold car for a while, then brought it into a steamy bar full of sweaty people, a significant amount of water would condense on the pickups, and soak into the coils. The water would also evaporate slowly, but be refreshed on every gig.

[savage]

I know that in old household wiring as the wire ages it's crystalline structure changes. It gets brittle and its resistance increases. Perhaps the same kind of thing is happening in the pickups. You could possibly prematurely age the wire by heating it either indirectly or by running current through it. Just a thought.

[David Schwab]

I don't think a resistor would have the same effect as loading the magnetic circuit with metal, eddy currents. I think those magnetic paints probably are ferrite which won't load the circuit either. I started another post on, is it possible to soften alnico magnetically? That stuff is awful hard yet the metals that make it up aren't hard metals. I know that SRV wrapped his pickups in copper tape yet if I do that I don't measure any change, but I didn't ground it either...

The paint has iron in it. I read the MSDS on it.

[David Schwab]

Not to hi-jack here but I wonder if this krylon could replace the expensive shielding paint?

Yes, you can. I'm not sure how much cheaper it is though.

http://www.muzique.com/lab/magpaint.htm

[David Schwab]

Just dropped an ally guard over a pickup , it changed the ACR and the inductance...acr went up inductance went down , hmmmm , funny that..

Eddy currents.