Microphonic feedback from PAF pickup. FIXED!!!

[Great Yawn]

I had a pickup that was giving me that high-pitched microphonic squeal if I came anywhere near an amp that was set just loud enough to play with a drummer. I thought I'd share how I fixed it, for future reference for anyone looking to fix a similar problem.

Problem
Curtis Novak JM-PAF bridge pickup in an AVRI65 Jazzmaster producing a high-pitched microphonic squeal. Not the kind of feedback you can use in a fun noiserock way, but the kind you get when you hold a microphone too close to the PA speakers, making everyone cover their ears and pull a lemon-eating face. Holding the strings, or taking them off your guitar will not affect this type of feedback.

Cause
Microphonic feedback is caused by small vibrations inside or against the pickup, or an air pocket between the pickup and the pickup cover. PAF pickups may be more susceptible to this because they are quite sensitive to any touch of the guitar and resulting vibrations and harmonics.

Troubleshooting
-Maybe the pickup needs to be wax potted, because the squeal is caused by vibrations inside the pickup?
Wax potting will alter the tone. There are many guitars that work fine without wax potting PAF pickups. Plus, it's not certain that the vibration is coming from inside the pickup. This should be a last resort.

-Could it be the pickup cover?
Take the strings from your guitar. Take off the pickup cover and stand near your amp set-up that would normally produce the squeal. Alternatively, leave the pickup covers on and push down on them to see if the squeal disappears.

Squeal disappears? Bingo. The problem is the space between the top of the pickup and the pickup cover. (This is why PAF pickups usually come with flat covers rather than curved ones.)

Solution (that worked for me)
Get those clay-like poster adhesives you can knead in the shape you want. Google 'Pritt Poster buddies' for an example. Get a couple of them together, make a little sausage, put the sausage on the top of the humbucker, on the bobbins, not on the polepieces. Flatten the sausage over that side of the pickup. Press pickup into the pickup cover. If working with a regular (metal) pickup cover: solder pickup cover to pickup the way it was before. If working with Jazzmaster: make sure there's enough padding under the pickup to hold the pickups against the cover, although the putty should make them stick together quite well.

I believe Jazzmasters are a perfect candidate for this problem, because pickups are not attached to the cover, and the pressure between the pickup and the cover is only applied by the foam underneath the pickup.

Some useful resources I encountered:
http://www.ryansguitars.com/2010/01/sto ... s-and.html
https://www.pafhumbucker.com/paf-pickups-covers.html

[sookwinder]

Basic acoustic design theory. To change the resonant frequency either stiffen the item or add mass.