Potting

[Paulkstadden]

This may seem like a silly question, but since I want to know as much as I can, and I've never heard anyone directly address this, I'll ask anyway. Other than eliminating microphonic feedback, does potting affect the tone of a pickup? I imagine there may be some harmonics that aren't present anymore once a pickup is potted, but I've never heard anyone say anything on it. Also, I've heard that epoxy potting does not penetrate the coils, and therefore does not stop microphonic feedback. Is this true? Still, there are people who either do not pot, use parrafin/beeswax, or epoxy. Are there other ways of eliminating microphonic feedback without potting?

Possum, I read on your site that the set you made for Jake E. Lee is not wax potted. Is there a reason for this? I'm very curious!

[Sock Puppet]

It must do...

Hi,

This list shows the dielectric constants of paraffin wax(2.1-2.5), beeswax(2.7-3.0) and cast epoxy resin (3.6):

http://www.clippercontrols.com/info/...constants.html

This implies that the inter-winding capacitance will increase by these factors which in turn will roll off some of the upper harmonics you mention.

I think you'll find most people here use something like an 80/20 mix of paraffin wax/beeswax for the low melting point (or beeswax alone).

Having said that, I remember posts on the old Ampage forum where someone was allegedly using wax crayons... though it could have been a wind-up

S.

[Spence]

Personally I only use paraffin wax unless I'm doing an early Fender replacement set with a mix of paraffin wax and black boot polish.

What is the dielectric constant for Cherry Blossom?

Anyone?

[Sock Puppet]

What is the dielectric constant for Cherry Blossom?

Anyone?

Dunno Spence, try the Doc Martens site.

What's the dielectric constant for lanolin, that well known wire drawing lubricant from Wales?

S.

[J S Moore]

I thiink the wax crayon bit was for real, it came up on the LP forum.

[Possum]

Jake E Lee

I don't pot any of my humbuckers, Jake's sound clip was done through a POD so he's not playing in front of 12 Marshall stacks on 10. I don't pot them because I mostly make PAF type pickups which were never potted, and most of my customers are blues guys who don't play stadium rock at deafening levels. If I did I would have to pot them....

[J S Moore]

Jimmy Page and Peter Green didn't seem to have a problem with un-potted pickups.

I do it either way, depending on what the customer wants.

[Sweetfinger]

Yup!

I use primarily parrafin, which gets a bit of crayon/beeswax/candle wax in it due to repotting of other previously/poorly done pups.

It does change the tone slightly by rolling off a tiny bit of highs, but more importantly, some of the "grooviness" of vintage pickups comes from the fact that they ARE slightly microphonic, and potting/solidifying will certainly kill that aspect, so I won't pot a valuable vintage pickup unless it is really unusable at even low to moderate volumes.

Other things to change if you want to eliminate microphonics are the springs. On any rock guitar, I'll change the pickup springs to silicone surgical tubing. Make sure no steel wool bits or string ends are stuck to your pickups as well.

[Paulkstadden]

Wow, that's all excellent info! Does tension and/or type of wind (scatter versus perfectly lined machine wound wiring) affect microphonic feedback? Anything else that can be used for potting other than the traditional materials?

[Spence]

Dunno Spence, try the Doc Martens site.

What's the dielectric constant for lanolin, that well known wire drawing lubricant from Wales?

S.

Allergic to lanolin and had to give up the sheep shagging. However, for those who'd like to try it, always get the sheep on the edge of a cliff. ....they push back better !

[Joe Gwinn]

What's the dielectric constant for lanolin, that well known wire drawing lubricant from Wales?

It's in the same range as paraffin wax and beeswax. It would probably make a good softener for potting waxes, and is very good at preventing corrosion.

On the matter of the dielectric constant of mixtures: The dielectric constant of a mixture of two substances A and B, whose dielectric constants are Ka and Kb respectively, is the weighted average by volume of the dielectric constants of the two substances.

For instance, take a potting wax consisting of 80% paraffin wax (Ka=2.1-2.5=2.3) and 20% beeswax (Kb=2.7-3.0=2.85):

Kab= 0.80(2.3) + 0.20(2.85)= 2.41= 2.4

This works even if one of the substances is air (K= 1.00), as is partly the case in unpotted pickups.

[David Schwab]

Speaking of paraffin wax and beeswax... there was a discussion over at the MIMF forum, where Clint Searcy did a photo essay on restoring some 1950's Le-Re pickups from a Finnish made Malmström lap steel.

The pickups had failed because the beeswax they were potted in caused corrosion that went all the way to the wire. It seems beeswax is acidic!

Should we be using that stuff?

I use potting epoxy myself.. but I'm not winding PAFs or Strat pickups.

[Joe Gwinn]

Speaking of paraffin wax and beeswax... there was a discussion over at the MIMF forum, where Clint Searcy did a photo essay on restoring some 1950's Le-Re pickups from a Finnish made Malmström lap steel.

The pickups had failed because the beeswax they were potted in caused corrosion that went all the way to the wire. It seems beeswax is acidic!

Should we be using that stuff?

It may be a purity issue. No wax is acidic. Or an environment issue: where did this failed pickup live? maybe the problem was ingress of beer.

In any event, there must be millions of pickups potted with beeswax, and very few have failed.

I use potting epoxy myself.. but I'm not winding PAFs or Strat pickups.

Epoxy works, but the danger with rigid potting is mismatches of temperature coefficients of expansion causing stresses large enough to break something. Humidity coefficients can also do this, although it's not likely to be a problem with pickups (which are physically small and largely made of impermeable strong materials).

[David Schwab]

It may be a purity issue. No wax is acidic. Or an environment issue: where did this failed pickup live? maybe the problem was ingress of beer.

That's not what I read when I looked up beeswax:

It is a tough wax formed from a mixture of several compounds including: hydrocarbons 14%, monoesters 35%, diesters 14%, triesters 3%, hydroxy monoesters 4%, hydroxy polyesters 8%, acid esters 1%, acid polyesters 2%, free acids 12%, free alcohols 1%, unidentified 6%

The main components of beeswax are palmitate, palmitoleate, hydroxypalmitate[1] and oleate esters of long-chain (30-32 carbons) aliphatic alcohols, with the ratio of triacontanylpalmitate CH3(CH2)29O-CO-(CH2)14CH3 to cerotic acid[2] CH3(CH2)24COOH, the two principal components, being 6:1.

The guitar was from Finland. Clint couldn't figure out what was causing the green corrosion all inside the pickup, and it even went past the paper tape and corroded the solder joints. When he melted out the wax it looked like this (see attached photo):

The pickups were sealed and filled with wax.

In any event, there must be millions of pickups potted with beeswax, and very few have failed.

This is true.

Epoxy works, but the danger with rigid potting is mismatches of temperature coefficients of expansion causing stresses large enough to break something. Humidity coefficients can also do this, although it's not likely to be a problem with pickups (which are physically small and largely made of impermeable strong materials).

There's also many pickups (and other circuits) out there potted in epoxy. I have a Hi-A pickup from 1972 which still works. I use epoxy specially made for encapsulating and potting ... not sure if it's different from "normal" epoxy. I get it from Mouser.

The last set of pickups I made I coated the coils with polyurethane after I wound them. I happened to have had a can and thought I'd give it a try.

[erikbojerik]

Or an environment issue: where did this failed pickup live? maybe the problem was ingress of beer.

Hehehe....Bruce Springsteen's old Esquire has a hole near the bottom of the body, so that Bruce's sweat can drain right on out.