Thoughts and feelings on foregoing potting

[David Schwab]

If you are using epoxy, do you really need wax?

Yes. I tried it without the wax, and ended up with microphonic pickups. The epoxy does not seep inside the coil all the way. I know this because I cut one of them open.

[FunkyKikuchiyo]

I'm not using the epoxy on the coils themselves, just on the assembly. I mentioned this because when I've had excessive microphonics, it has been because of a loose part on the pickup rather than the coil itself, and the parts within this pickup are quite rigid.

Perhaps I just need to pot them earlier before assembly. I was reluctant to do this because assembly means gluing it all together, and effectively doing that means VERY thoroughly cleaning off the wax or else it just falls apart. Dipping the whole thing makes a colossal mess.

I think I may do a test set through a full stack or something just to see how they work, though.

[big_teee]

You can do a pretty good microphonics test by just temporarily hooking the pickup to a jack.
I have a test Jack, with a short cable, and I use small wire nuts to connect it to the pickup cable.
I hold the pickup in front of the amp.
I test it with different gain and volume.
If it will squeal it will do it then.
That's a real good way to test a tele bridge pickup with a base plate.
Good Luck,
T

[Bruce Johnson]

To me, potting is all about durability. Magnet wire is very fragile. Putting a loose coil of thousands of turns of it into a machine that's going to spend its whole working life vibrating at a wide range of frequencies is asking for eventual failure. If the wire can move around, it's eventually going to fatigue and snap. I'm sure that Fender potted their pickups to reduce failures, not to try to prevent microphonics or shape the tone. They used wax because it was cheap and fast, and did a pretty good job. I say "pretty good" because Fender pickups still have lots of failures.

On my pickups, I use epoxy, a special type that's about as thin as CA glue. It's a slower process than wax, but I don't care. Then, I cast the coil and shield assembly in a heavier epoxy. I don't want my pickups to ever fail.

If you don't want to work out a wax process, you should at least use some CA glue to provide some mechanical support to the wire.

[marku52]

I wax pot the bobbins and magnets onto the steel base plates, and then when I install the can, I wax pot that on as well. If anything in that magnetic circuit can move, then it can be microphonic. Nickel Silver is slightly magnetic. A neo magnet will stick to it, and I notice that the pickup inductance increases slightly once the pickup is canned up. Hence if the can can move, it will be microphonic.

I once had a CBS telecaster that squealed like a stuck pig. CBS decided that wax potting was unnecessary. I don't want any of my customers to be subjected to that problem.

[FunkyKikuchiyo]

I wax pot the bobbins and magnets onto the steel base plates, and then when I install the can, I wax pot that on as well. If anything in that magnetic circuit can move, then it can be microphonic. Nickel Silver is slightly magnetic. A neo magnet will stick to it, and I notice that the pickup inductance increases slightly once the pickup is canned up. Hence if the can can move, it will be microphonic.

I once had a CBS telecaster that squealed like a stuck pig. CBS decided that wax potting was unnecessary. I don't want any of my customers to be subjected to that problem.

If it is true that something that is ferromagnetic needs to be able to move, then I may be in the clear in that regard. These things are stupidly rigid already. It is only the coil itself that would be able to move, as it is wound only with moderate tension. They are kinda over-engineered, and perhaps that is the bright side of it.

I'd be curious if those CBS coils had higher failure rates from broken/shorted coils because it didn't have the wax protecting them...

[Bruce Johnson]

It seems to me that if the wire coil can move in relation to the magnets, then you're going to be creating a signal, right?

I'm not a veteran of pickup repair, but my understanding is that the most common way that pickups fail is that the end of the magnet wire breaks right near the termination point. It can be from mechanical or thermal movement pulling on the wire, or poor soldering technique, or something like that. The second most common failure is a break down inside the coil, usually caused by incomplete potting. The coil vibrates until the wire fatigues out and snaps. Or, the bouncing wires rub off insulation and short against each other or to ground. Am I right about this?

[marku52]

It seems to me that if the wire coil can move in relation to the magnets, then you're going to be creating a signal, right?
?

That's the reason that fenders squeal, for certain. There is no other iron to be moveable, and the magnets are stiffly pressed into the forbon, so for sure it is the wire moving. Have you ever heard a transformer "sing"? Often this is the case with the power trans in a switchmode power supply, the sharp turn-on and off edges have a lot of harmonics to stimulate the trans. And in the fast changing magnetic field, the wires move if not potted. Hence the transformer sings. Same microphonic effect, but in reverse.

In my pickups, I also have a steel baseplate and a NS can to worry about, either of them moving could be a problem as well.

for failed fenders, I have seen where the alnico magnets corrode, and because fender didn't insulate the magnets from the first winds, the corrosion sneaks down the magnet into the coil and opens the first winds. Of course the outer winds aren't much protected from customer abuse, if they take the thing apart, either.

[big_teee]

I pot evereything I sell. Some Pickups get Double Potted.
I hook up every pickup to a test jack and connect to my test marshall in the shop.
If it squeals back in the pot it goes.
Tele Bridge Pickups with base plates are the worst.
The Amplifier is the biggest uncontrollable problem with microphonics.
You can't control the Microphonics of the Amp, but by Potting You can control the Microphonics of the Pickup.
What you can get by with, with one amp, won't work with another amp setup.
Keep Rockin!
Terry

[StarryNight]

I'm just rewinding an older Dimarzio Super Distortion at the moment and I was surprised to see that there was absolutely no potting on the coil whatsoever. The magnet and metal shim was epoxied to the hex screws and baseplate but no potting on the coils.

[big_teee]

I'm just rewinding an older Dimarzio Super Distortion at the moment and I was surprised to see that there was absolutely no potting on the coil whatsoever. The magnet and metal shim was epoxied to the hex screws and baseplate but no potting on the coils.

Maybe the Basis, was that the vibrating Coils aids in the Distortion???
T

[Bryan Jeppson]

I pot my coils in Bullseye shellac. For pickups I make for my own use, I leave them unpotted. Maybe it's all in my imagination, but I think unpotted pickups have more tonal character. To me, shellac potted coils are the best compromise for durability and anti-feedback versus tonal response.

[FunkyKikuchiyo]

Thanks guys!

Between what is here and what came up in a different thread, I'm liking the idea of trying the shellacs and/or epoxies. For this design, it sure seems more practical than wax potting, since the dipping makes a big mess of this design.

[big_teee]

You talk about the mess of wax potting.
Normally if your pickup is hot enough, long enough while potting.
The cleanup is easy.
The wax stays a liquid for a while, and I just blot it up with a paper towel.
That way you can get all exposed wax off the outside of the pickup.
Sounds like you have figured out what you need.
Good Luck,
Terry

[David Schwab]

I used to use shellac and I have used polyurethane. I stopped using them because I had some pickups that were microphonic, and I had realized that the shellac didn't always dry all the way.

Epoxy also does not seep all the way into the coil, unless you are doing it like Bruce does. I epoxy encapsulate my pickups, and I have cut open bad pickups and saw how far the epoxy went. It did not stop them from squealing.

So now I use wax.