Originally posted by David Schwab
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Thoughts and feelings on foregoing potting
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I generally pot all of my pickups except the butyrate P.A.F types. Like Terry and others I want mine to last a long time with no issues. Recently I have been making some Firebird (ish) type Mini-humbucker prototypes for a custom electric banjo. I wanted the resonant peak to be as high as possible for the banjo sound. I noticed that after I potted them the peak dropped down from about 15 kHz to about 13.5 kHz. Has anyone else noticed the peak dropping after potting? I use 80 % parrafin 20% beeswax and I potted them at 150 degrees. I have a good temperature controller on my wax vat.www.sonnywalton.com
How many guitars do you need? Just one more.
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Originally posted by copperheadroads View PostReady made Shellac has a shelf life & should be tested to see if it dries before using
Wax is quick and does the job.It would be possible to describe everything scientifically, but it would make no sense; it would be without meaning, as if you described a Beethoven symphony as a variation of wave pressure. — Albert Einstein
http://coneyislandguitars.com
www.soundcloud.com/davidravenmoon
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Originally posted by David SchwabIt was a fresh can well within its shelf life. But shellac takes a week to fully cure, and I don't have time for that. I use to have a rack of bobbins sitting to dry, and that slowed down everything. Now I can get the pickups assembled the same day they are wound. I encapsulate my pickups in epoxy, so I'm sure that helped prevent them from drying. I don't know how much of shellac's curing is from evaporation vs. cross linking. The fact that it stays liquid in the can leads me to believe it's from evaporation. Therefore the inside of the coil just isn't going to evaporate, especially after the pickups have been encapsulated. Same was try of the polyurethane.
Wax is quick and does the job.
The critical factor related to potting a pickup is the Dielectric Constant (D.C.) of the potting material. Epoxy resin -3.6; Wax - 2.4 to 6.5, Paraffin wax - 2.1 to 2.5. Typically, the Dielectric Constant of dry air is 1 and the higher the D.C. number the worse job of insulating it does as it makes the capacitance between turns higher. Pickups typically have about 100pfs of capacitance and the guitar cable capacitance tends to dwarf this value making the pure pickup sound difficult to hear unless the pickup is buffered near or inside the guitar. Anytime the air space inside a pickup is filled with some material, the space will have a D.C. of a little higher than air so the self resonance should be lower.
Here is an easy test to confirm this. Measure the pickup self-resonance before potting. Then measure it after potting with the coil at the same temperature as the previous measurement. You should see a slightly lower resonant frequency indicating a raise in coil capacitance where the potting material replaces the air space between the coil windings.
Joseph Rogowski
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Originally posted by marku52 View PostNickel Silver is slightly magnetic. A neo magnet will stick to it, and I notice that the pickup inductance increases slightly once the pickup is canned up.It would be possible to describe everything scientifically, but it would make no sense; it would be without meaning, as if you described a Beethoven symphony as a variation of wave pressure. — Albert Einstein
http://coneyislandguitars.com
www.soundcloud.com/davidravenmoon
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