Yesterday, I wrote some explanations on other threads about the mechanical aspects of encapsulating and potting pickups, how it affects the final signal from the pickup.
I'm copying these posts here, because I think these are useful to us pickup builders. The question was: What is the purpose of sealing pickups with epoxy?
Yes, encapsulating the pickup in epoxy is mainly about sealing up the pickup, completely and permanently, to make it more durable and resistant to physical damage, temperature changes, moisture changes, age, etc.
The potting, with wax or the thin epoxy, is done to stop the microphonics of the wires in the coil vibrating.
Old time pickups, like many of the classic Fenders, weren't potted thoroughly enough, and some of them would have some microphonics. But, some players got to like those microphonics as part of the character of the sound. More in guitars than basses. That high raspy squeal in a Clapton solo. That became part of the sound of electric guitars. But it wasn't consistent from one pickup to the next. Some pickups had no microphonics, and some had too much, where it was irritating. But the ones that had just the right amount of "squeal" were treasured.
And a whole industry of aftermarket Boutique Pickup makers worked to figure out how to make pickups that had that same sound. The magic of the Squeal was all about controlling the depth of the potting of the coils. Allowing the wires to vibrate, just a little bit.
When active systems appeared, the Squeal lost its appeal. It was very difficult to make the mechanical microphonics sound good when the signal is being boosted by a Hi-Fi preamp. So, on pickups to be used with active preamps, the builders fully potted them to make sure they didn't have any microphonics. Those became Active pickups. Not a whole lot different from old-fashioned Passive pickups. A slightly different formula to widen the frequency range, flatten the EQ curve and clean up those messy microphonics. And the builders concentrated on creating the Squeal sound with electronic circuits, in pedals or in the amp.
Which is a better Squeal? Created mechanically by microphonics in a passive pickup? Or created electronically by circuits, processing a base signal from a clean active pickup? I dunno. They are slightly different, but both can be good, if done well. Take your pick.
Epoxy encapsulation around the outside of the coils has almost nothing to do with internal microphonics and Squeal. But it does help to reduce external microphonics. That's the low frequency Thump you hear in the signal when you tap your fingers on the bass. It's caused by the entire coil assembly bouncing inside the housing when you physically hit the bass. Usually not too bad on a passive bass, but it can be really annoying with an active system amplifying it. That's a big part of the reason why builders of Active pickups started filling their housings with epoxy, to cut down the Thump.
But the main reason was to seal them up, permanently. Fender-style pickups with no encapsulation are fragile. They fail over time. Mostly because the wax potting dries out over the years and cracks, allowing too much microphonics or breaking the teeny wire. The beautiful squeal turns into an ugly scream, then silence. It's dead.
The good thing about old non-encapsulated Fender pickups is that, when they fail, they can be opened up and rebuilt. Cut off all the wire and rewind the bobbin, and put it back in the cover. Trying to match the original coil specs and level of potting. That's the magic of the pickup rewinding specialists.
Pickups that have been encapsulated with epoxy are permanently sealed up. They can not be opened up and repaired. But they should never fail. Sealed against moisture and temperature and mechanical wear. They should work forever, unless physically crushed. But you can't repair or modify them.
Those are the tradeoffs.
Sealing up the pickup so that someone else couldn't easily dissect it and learn the Secret Formula, was an extra side benefit. But not the driving reason for the epoxy. It's for durability.
I'm copying these posts here, because I think these are useful to us pickup builders. The question was: What is the purpose of sealing pickups with epoxy?
Well, there are two separate things here: Potting and Encapsulation.
Potting is done to the inside of the coil, using something to soak down into the full depth of the coil, between all the wires. This lightly glues the bundle of tiny wires together into a soft lump. This is to prevent Internal Microphonics, which is caused by the wires inside the coil vibrating, from the overall vibration of the bass. Soaking the coil with a soft "glue" stops the microphonics.
The traditional way to do Potting of pickup coils is to dunk them in hot melted wax. The hot wax soaks all through the coil and then cools off into a semi-soft state. That's how most magnetic pickups have been made for the last 70 years or so. Wax Potting is fast and simple in a production line.
Now, there are a few of us small pickup makers these days (including myself) who do the Potting with epoxy, rather than wax. It's a special epoxy that has a very low viscosity, about like water. It soaks all the way through the coil and glues the little wires together, same as wax does.
Encapsulation is a different step. That's adding a thicker coating or material on the outside of the coils (which have been previously Potted), as a protective layer to prevent physical damage to the coils. Encapsulation may be done with epoxy, or a thicker wax, or not at all.
Classic Fender-style pickups have the coils Potted with wax, and then inserted in molded plastic covers with no Encapsulation. Other style pickups have the potted coils inserted in plastic covers, and then the inside space is filled with more wax. A thicker wax. That's Wax Encapsulation, done over top of the Wax Potting.
Some pickup makers use epoxy for the Encapsulation. A layer of thicker epoxy may be wiped onto the outside of the Potted coils as a harder protective coating. Then the coils are inserted into the plastic covers. Or, the potted coils are inserted into the plastic covers and the space inside is filled up with thicker epoxy. The coils are effectively cast in epoxy inside the plastic cover.
And, the Encapsulation epoxy can become the cover itself. The coils are suspended in a silicone rubber mold, and epoxy is poured in around them to fill the mold. The coils are permanently cast into the epoxy, and the epoxy becomes the outer protective shell.
Those are different ways to do the mechanical construction of magnetic pickups.
A follow-up answer, with more detail:Potting is done to the inside of the coil, using something to soak down into the full depth of the coil, between all the wires. This lightly glues the bundle of tiny wires together into a soft lump. This is to prevent Internal Microphonics, which is caused by the wires inside the coil vibrating, from the overall vibration of the bass. Soaking the coil with a soft "glue" stops the microphonics.
The traditional way to do Potting of pickup coils is to dunk them in hot melted wax. The hot wax soaks all through the coil and then cools off into a semi-soft state. That's how most magnetic pickups have been made for the last 70 years or so. Wax Potting is fast and simple in a production line.
Now, there are a few of us small pickup makers these days (including myself) who do the Potting with epoxy, rather than wax. It's a special epoxy that has a very low viscosity, about like water. It soaks all the way through the coil and glues the little wires together, same as wax does.
Encapsulation is a different step. That's adding a thicker coating or material on the outside of the coils (which have been previously Potted), as a protective layer to prevent physical damage to the coils. Encapsulation may be done with epoxy, or a thicker wax, or not at all.
Classic Fender-style pickups have the coils Potted with wax, and then inserted in molded plastic covers with no Encapsulation. Other style pickups have the potted coils inserted in plastic covers, and then the inside space is filled with more wax. A thicker wax. That's Wax Encapsulation, done over top of the Wax Potting.
Some pickup makers use epoxy for the Encapsulation. A layer of thicker epoxy may be wiped onto the outside of the Potted coils as a harder protective coating. Then the coils are inserted into the plastic covers. Or, the potted coils are inserted into the plastic covers and the space inside is filled up with thicker epoxy. The coils are effectively cast in epoxy inside the plastic cover.
And, the Encapsulation epoxy can become the cover itself. The coils are suspended in a silicone rubber mold, and epoxy is poured in around them to fill the mold. The coils are permanently cast into the epoxy, and the epoxy becomes the outer protective shell.
Those are different ways to do the mechanical construction of magnetic pickups.
Yes, encapsulating the pickup in epoxy is mainly about sealing up the pickup, completely and permanently, to make it more durable and resistant to physical damage, temperature changes, moisture changes, age, etc.
The potting, with wax or the thin epoxy, is done to stop the microphonics of the wires in the coil vibrating.
Old time pickups, like many of the classic Fenders, weren't potted thoroughly enough, and some of them would have some microphonics. But, some players got to like those microphonics as part of the character of the sound. More in guitars than basses. That high raspy squeal in a Clapton solo. That became part of the sound of electric guitars. But it wasn't consistent from one pickup to the next. Some pickups had no microphonics, and some had too much, where it was irritating. But the ones that had just the right amount of "squeal" were treasured.
And a whole industry of aftermarket Boutique Pickup makers worked to figure out how to make pickups that had that same sound. The magic of the Squeal was all about controlling the depth of the potting of the coils. Allowing the wires to vibrate, just a little bit.
When active systems appeared, the Squeal lost its appeal. It was very difficult to make the mechanical microphonics sound good when the signal is being boosted by a Hi-Fi preamp. So, on pickups to be used with active preamps, the builders fully potted them to make sure they didn't have any microphonics. Those became Active pickups. Not a whole lot different from old-fashioned Passive pickups. A slightly different formula to widen the frequency range, flatten the EQ curve and clean up those messy microphonics. And the builders concentrated on creating the Squeal sound with electronic circuits, in pedals or in the amp.
Which is a better Squeal? Created mechanically by microphonics in a passive pickup? Or created electronically by circuits, processing a base signal from a clean active pickup? I dunno. They are slightly different, but both can be good, if done well. Take your pick.
Epoxy encapsulation around the outside of the coils has almost nothing to do with internal microphonics and Squeal. But it does help to reduce external microphonics. That's the low frequency Thump you hear in the signal when you tap your fingers on the bass. It's caused by the entire coil assembly bouncing inside the housing when you physically hit the bass. Usually not too bad on a passive bass, but it can be really annoying with an active system amplifying it. That's a big part of the reason why builders of Active pickups started filling their housings with epoxy, to cut down the Thump.
But the main reason was to seal them up, permanently. Fender-style pickups with no encapsulation are fragile. They fail over time. Mostly because the wax potting dries out over the years and cracks, allowing too much microphonics or breaking the teeny wire. The beautiful squeal turns into an ugly scream, then silence. It's dead.
The good thing about old non-encapsulated Fender pickups is that, when they fail, they can be opened up and rebuilt. Cut off all the wire and rewind the bobbin, and put it back in the cover. Trying to match the original coil specs and level of potting. That's the magic of the pickup rewinding specialists.
Pickups that have been encapsulated with epoxy are permanently sealed up. They can not be opened up and repaired. But they should never fail. Sealed against moisture and temperature and mechanical wear. They should work forever, unless physically crushed. But you can't repair or modify them.
Those are the tradeoffs.
Sealing up the pickup so that someone else couldn't easily dissect it and learn the Secret Formula, was an extra side benefit. But not the driving reason for the epoxy. It's for durability.
