из
MARTIN KOCH
Building Electric Guitars
Potting pickups
Microphonics will be a problem when pickups are wound too
loosely and the loose wire subsequently behaves like a microphone,
generating an additional alternating current inside the
magnetic field and thus making the pickup susceptible to
feedback or causing it to pass on fretting noises or clapping on
the body. To fix the windings in place, immerse the finished coil
in hot, liquid wax of a maximum temperature of 65 degrees
Celsius (150°F). At this temperature, the pickup is absolutely safe
and nothing can go wrong. A deep fryer would be ideal for this
purpose, but it is probably not worth ruining one for the sake of
just very occasionally immersing the odd pickup in it. I put a
metal container into a hot water bath to heat the wax (5).
Always use a mixture of paraffin and beeswax for potting
pickups. Pure paraffin wax is too brittle and pure beeswax has a
melting point that is too low. By adding about one part of
beeswax to four parts of paraffin wax, you get a perfect mixture.
Always check the temperature, for instance with a meat thermometer.
As the wax can be much hotter close to the container
walls and at the bottom, try to steer clear of these. By putting
small pieces of wood at the bottom of the container, you can
make sure that the pickup is safe from making contact with it.
Leave the pickup in the wax-bath for 10 to 20 minutes, but at
least until there are no more air bubbles rising. Wear eye protection
when placing the pickup into the wax-bath, just to make
sure.
Pickups can also be encapsulated with epoxy resin. This kind
of treatment, however, has the disadvantage of making the
pickup inaccessible afterwards. Apart from that epoxy resin does
not penetrate the windings as well as wax but just sticks to the
outside of the coil. Wax is also easy to remove by re-heating the
pickup. Immersing the pickup in wax is an environmentallyfriendly
method used by a lot of manufacturers.
A bit of physics
While the pickup was in the waxbath,
I connected it to an ohmmeter
and found that its resistance had
risen: the cold pickup had shown a
resistance of 10K ohms, the hot
pickup showed 12.57K ohms.
What can we learn from that?
Electrical resistance increases and
decreases with temperature.
Because wax is extremely
flammable, I recommend that
you always pot your pickups in
a safe place outdoors and that
you keep a lid at hand for
quickly covering the pot in
case of fire. Always use a
thermometer to ensure a
temperature of 65 degrees
Celsius (150°F) is never
exceeded. Since paraffin gases
can easily catch fire, you must
never even attempt to heat the
wax in a microwave oven.
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