If you are having microphonic problems without the cover, I would first try to solve the microphonic problem by checking a few things.
- Make sure both bobbins are firmly secured to the bottom plate.
- Carefully tighten the 4 bobbin mounting screws. Do not over tighten or strip the mounting holes in the bobbins.
- Make sure the magnet is firmly secured and does not slide back and forth.
- Make sure the pole pieces are not loose in the bobbins. They can vibrate and cause feedback. Especially in bobbins where the neck of the screw isn't secured.
- Make sure the stud pole pieces are not loose.
- Check to see that the metal spacer is firmly secured between the bobbin and bottom plate.
- The height adjust springs can vibrate and cause noise or interference with the pickup.
- Make sure the pickup is firmly attached to the mounting ring. Pickups that are loose in the mounting rings can flop around and also make unwanted noise in the instrument.
- I don't like to wax pot various models of pickups because it can change the appearance or decrease the value of the pickup. If the parts are loose try using a small amount Vaseline to lubricate the metal parts to cushion the vibration that can cause feedback. It is easy to remove and will not damage the parts.
- Wax potting should only be done by an experienced repairman under controlled conditions because of the safety factor and damage that could occur with the plastic bobbins.
- Installing a metal cover should be done with proper clamping to firmly hold the cover while being soldered to the bottom plate. Having a cover that is loose on a pickup will only increase microphonic feedback and should be carefully wax potted, quickly and preferably in a vacuum system using specified temperatures.
WRITTEN ON JUNE 12, 2015, BY