potting

[dazzlindino]

Does anyone here use epoxy for potting guitar pickups,and does it control high gain amp feedback better than wax potting?
Have a guy straight out of spinal tap that does everything on 11... myself ,I only turn up to ....say 10 and a half, so go figure

[David Schwab]

I use epoxy potting, but I'm making bass pickups, so I can't tell how it would help with high gain guitar pickups, but they are solid as a rock, so I can't imaging they would feedback.

But you need a closed cover. I guess you can do it with screw poles, but you have to wax them first.

I use special epoxy made for potting.

[SK66]

It can, and it can also cause it's own feedback, but due to vibration and not "microphonics"

[dazzlindino]

I use epoxy potting

But you need a closed cover.

I use special epoxy made for potting.

.....and the type / brand you use if I may dare ask?

[David Schwab]

.....and the type / brand you use if I may dare ask?

MG Chemicals Black Epoxy Encapsulating and Potting Compound.

I get it from Mouser. (<-- link to product)

They make clear also.

[dazzlindino]

Thankya, thankya very much..........

[NightWinder]

???

Dave, do you pot the coils individually...then assemble and then fill with epoxy? Does it expand or pour and what you get stays???

[David Schwab]

Dave, do you pot the coils individually...then assemble and then fill with epoxy? Does it expand or pour and what you get stays???

I dip the assembled coils in a can of polyurethane, let it drip a bit, and let it sit over night to dry.

Then I assemble the pickup in the case, test it out real quick, and then mix and pour the epoxy in the cases. Some of my pickups have back covers with the connections, so I sit that on top of the epoxy.

It doesn't expand at all in my experience. It takes 24 hours to cure, but is a bit tacky at that point, so I wait 48 hours before I sent the pickups to the customer.

[NightWinder]

...

have you ever waxed the coils first, then filled with epoxy? I wonder if that would creat some trapped air and cause microphony??

[David Schwab]

EMG wax the coils before they epoxy them. I don't see how the epoxy will stick to the wire, but that's what they do.

[Joe Gwinn]

EMG wax the coils before they epoxy them. I don't see how the epoxy will stick to the wire, but that's what they do.

Putting a "buffer coat" on components before epoxy potting is very common, as it allows items of different coefficients of thermal expansion to coexist without tearing each other apart. The buffer coat can be anything soft that is chemically compatible with the components and the potting agent.

[SK66]

I don't think you WANT the epoxy to impregnate/ stick to the coil wires.
Other than coating during winding I don't think you can ever get a perfect/complete impregnation of the coil; maybe not even if done during winding.
Having this "buffer zone" helps prevent the "vibration feedback" I noted earlier. I think if you just quickly dip the coils then epoxy pot like DAvid said, the effect would be very similar to unpotted coils. If you wax pot then epoxy pot, it's a potted pickup.
In my mind, epoxy potting is just a more "secure" method of construction, not "potting" in the traditional sense. I don't make pickups this way so I shouldn't be considered "an authority" on the subject.

[David Schwab]

OK, I see the point here... but what about bondable magnet wire?

One example is Q-Tuner pickups. They have free standing air coils wound with bondable wire, which after it's been bonded into a free standing shape (in an oven) is molded into a pickup with epoxy.

I can see that wax, being soft, would have a damping quality. But if your coil is bonded as one solid mass, it's only going to vibrate along with the rest of the substrate, which in this case is the cured epoxy resin.

I think of potting as making sure you don't have loose windings. Along with wax, things like lacquer and vanish have been used, and those of course dry much harder than wax.

In my case I'm dipping the coils into polyurethane (and it's not a quick dip, I let them sit there for a few minutes) to glue the windings together. The epoxy is really for structural integrity, and to prevent casual noisy people from looking inside.

Some of my early pickups skipped the poly step, and I haven't had any problems with microphonics or feedback. I really started the poly step because I was concerned the epoxy might not get inside the coil, even though it flows freely. It is epoxy potting compound after all. I don't see a problem with having the coils cemented together.

I mean, why did Gibson and others epoxy pot their pickups, when they could have just done wax? I doubt those Super Hubuckers were wax potted first, and I know that Bill Lawrence pickups are not. I just followed these examples.

A Q-Tuner pickup, which isn't trying to hide anything!

[soundmasterg]

How would you fix a pickup that has already been epoxy potted and is microphonic?

I've got a Rickenbacker 230 and one of the pickups broke a wire and I couldn't fix it, so RIC stuck one on ebay and I bought it last year. It is one of their HB2 humbuckers and isn't made anymore and is moderately rare. It is made mostly likely a typical Gibson style, but there is a samarium cobalt bar magnet on the bottom along with a circuit board where the wires attach, and the whole thing is epoxied. It works fine, except that at higher volumes it will squeal and nothing I do seems to fix the problem. I assume the potting is loose?

Wish I could fix the other one as it sounds much better too.

Greg

[David Schwab]

I doubt there's anything you can do about it.