a little thought on potting

[dpm]

Not sure if this has been discussed before, I couldn't find it by searching so here's a brand new thread[/game show voiceover]

Anyways... wax shrinks as it cools, thus pulling the coil windings closer to each other which, I assume, alters tone. Has this been talked about before? I've read about dielectrics and wire movement (resonance), but I don't recall anything about alterations to proximity in potting discussions.

[Spence]

" Anyways... wax shrinks as it cools, thus pulling the coil windings closer to each other "

It shrinks yes. but it doesn't pull the coil windings closer together.

[dpm]

Sorry Spence, I don't understand. How can the windings not be compacted a little by the shrinking wax? The wax takes the place of air present in the coil, then that waxy mass shrinks a little.

[Spence]

Yes but it doesn't form an outer crust and then pull the wire tight. It just slips past the windings as it contracts. Try it. If it did do that I think it would be a bit of a bonus.

[Mark Hammer]

If the wax had adhesive properties, like varnish, that would be one thing. It would bring the wire along with it as it migrated towards the polepieces, But the wax really only fills up the spaces fior the purposes of reducing the amount of play in the wire coil. If anything, I would expect there to be greater risk of microphonics as any space-filling wax contracts.

[DrStrangelove]

Wax as a damping compound?

If anything, I would expect there to be greater risk of microphonics as any space-filling wax contracts.

If the space-filling wax contracts slightly,
then the microphonic resonance will move
up in frequency and down in amplitude --
if you assume that the wax is hard enough
for a winding to bounce off of it.

I'm wondering if the properties at issue are
the elasticity and damping of the potting compound.
If a winding is shaking, the motion will damp out
faster because of the wax.

Steve Kersting of SK Guitar Specialties mentions using
an elastic vinyl sanding sealer for potting pickups.

You think the sealer is slightly elastic?

-drh

[David Schwab]

Steve Kersting of SK Guitar Specialties mentions using an elastic vinyl sanding sealer for potting pickups.

You think the sealer is slightly elastic?

I wonder if that's vinyl sealer? Regular lacquer based sanding sealer is kind of soft. Vinyl sealer could be good to use.

This is interesting... I'm making a wooden cover for a Basslines ceramic MusicMan pickup. So I had to remove the bobbins from the cover. I noticed looking at the ends (the pickup has foil shielding just on the sides) the coil looks really shiny and hard. I couldn't get a finger nail in there, so I pealed the foil from the side so I could touch it, and it's potted with something hard that looks like urethane or something. It's hard as a rock and very shiny.

They are very bright sounding pickups. I wonder how the potting agent used affects the tone.

In the photos it doesn't look as shiny as it is, and what looks like wax is where the foil was stuck to the potting agent.

[mkat]

This is interesting... I'm making a wooden cover for a Basslines ceramic MusicMan pickup. So I had to remove the bobbins from the cover. I noticed looking at the ends (the pickup has foil shielding just on the sides) the coil looks really shiny and hard. I couldn't get a finger nail in there, so I pealed the foil from the side so I could touch it, and it's potted with something hard that looks like urethane or something. It's hard as a rock and very shiny.

That's interesting because the alnico 5 version isn't shielded and is wax potted.

[David Schwab]

That's interesting because the alnico 5 version isn't shielded and is wax potted.

I think they made the alnico pickup like the original. I have a customer that puts the ceramics in all his Jazz basses. One of them had an alnico model. They sound very different, so the ceramic is their own interpretation of the MM pickup.

[mkat]

I think they made the alnico pickup like the original. I have a customer that puts the ceramics in all his Jazz basses. One of them had an alnico model. They sound very different, so the ceramic is their own interpretation of the MM pickup.

Is the ceramic version hotter, more susceptible to noise (maybe due to the higher frequencies)? Just wondering why it needs shielding.

[David Schwab]

Is the ceramic version hotter, more susceptible to noise (maybe due to the higher frequencies)? Just wondering why it needs shielding.

They list it as a hotter pickup. It's actually lower resistance than the alnico version. For the 4 string version he lists each coil on the alnico as 4.18K and the ceramic as 2.6K. Likewise with the 5 string he lists the ceramic as 2.9K for each coil, and he lists the two coils in parallel on the alnico as 5.01K. So that would be 10K for each coil.

That would make sense since the big steel poles would raise the inductance, so you need less winds on the coil.

I think they just shielded the ceramic because they weren't following the original and it should be shielded, just as it's potted differently.

But I'm just guessing.

[dpm]

Interesting replies. As it cools the wax certainly does have adhesive properties. It clings. Dip your hand in some and let it harden. It grabs as it shrinks. Pour some on your benchtop and tell me it isn't a bitch to remove! Of course beeswax and paraffin aren't the greatest of gluey waxes, but they do have some grab. Apparently microcrystalline adheres well, and in surfboard waxes they use something called vistanex. Anyone ever heard of it?

[Mystic]

I use pollyurethane and I only apply it after the coil is wound.

[David Schwab]

I use pollyurethane and I only apply it after the coil is wound.

I do the same thing.

[mick]

Just measured a coil before and after potting , ...same size....