Have you boiled your pickups?
Effectively, that’s what I’m doing here. These Jag pickups are taking a bath in a pot of hot wax.
When we talked about pickups a little while back, we discussed the fact that they were, for all intents and purposes, a big coil of wire and some magnets. Sometimes, the windings of that coil can move around a tiny bit (sometimes vibrating in sympathy with the note being played or just as you jump around the stage). This movement can be ‘picked up’ and added to the amplified sound which can result in nasty feedback. Pickups with this issue are often referred to as being microphonic.
Soaking in hot wax—called potting the pickup—allows the liquid wax to seep through the gaps between the windings and the other hardware (base-plates and so on). Once the wax cools, it solidifies in these gaps and helps prevent that movement. It’s important that the pickups are soaked for a while. When they warm to the same temperature as the wax, that ensures good penetration deep within the coils. You’ll notice a bubble in the photo—these continue to pop out slowly as the wax penetrates.
Wax tends to be the most common potting material as it’s easy to apply and makes it possible to disassemble the pickup in the future if the need arises. Lacquer and even epoxy have been used from time to time but neither penetrates as well as wax (they’re too thick) and they cure into impenetrable, hard, pickup-shaped lumps. Forget about disassembling one of these.
There are a couple of things worth mentioning on this subject:
Firstly, many of the most sought-after tones come from un-potted pickups. Some tones/styles can benefit from a very slight microphonic edge.
Secondly, it’s not necessarily a panacea. Potting can help reduce microphonic feedback but there can be many other contributors to feedback. If you’ve a problem, it’s worth considering everything in your signal chain.