From: till@acid-rain.lucid.com (Don Tillman)
Subject: Re: Ibanez pickups hum
Reply-To: till@lucid.com
Organization: Lucid, Inc.
Date: 28 Sep 92 10:39:28

   Date: Sat, 26 Sep 1992 22:25:19 GMT
   From: META000 <META@UNB.CA>
   Organization: The University of New Brunswick

   Althoughthe technology for producing pickup coils is pretty damn
   good, there are sufficient differences that occasionally crop up,
   such that the two coils in one "humbucker" are not matched enough to
   buck the hum completely.  It's my understanding that the factory
   folks often take coils off the line and sort them into bins with
   specific impedance ranges.  Any two coils from the same bin will be
   much more alike in impedance than two coils from separate bins.

Not true.  Factories use a digital counter to count of the number of turns
being wound on a coil.  Much easier, faster and more consistant.  If you
wind coils yourself, a coil winder with a turns counter is a godsend.

   Fine.  IF it happens that somebody ain't doing their job right, you
   can end up with a pickup where the impedance of one coil is a bit
   different from the other.  We're talking a few per cent here, but
   not much more.  Let's give the folks who work for Larry and Seymour
   a bit of credit!

   If you are delicate and graceful with a soldering iron, you can
   improve the tone and noise/hum of your humbucker in the following
   manner:

   1) Remove the pickup entirely from the guitar (sorry).

   2) Detach all relevant leads so that you have exposed two contacts
   for each pickup coil.

   3) Get hold of a 4 1/2 digit ohm-meter (3 1/2 may not be precise
   enough), and measure the electrical resistance of each coil.

   4) If they are within 1% of each other (e.g., one coil is 5000 ohms,
   and the other is 5050 ohms), then any annoyingly loud hum may not be
   coming from your pickups (although there are exceptions to this).

   5) If they are more than, say 0.5% different, take the coil with the
   greater resistance, and GENTLY! lift the wire at the end of the coil
   (i.e., on the outside) and unwind it approximately ONCE for each
   ohm, until you have reduced the coil resistance by thedifference
   between the two coils (e.g., if you needed to reduce the 5050-ohm
   coil in the above example, take off about 46 turns) scrape the
   insulation off at the appropriate part and measure the new
   resistance.  When the two pickups are within 0.1% of each other,
   you'll have done about the best that can conceivably be done.  I did
   this with a home- brew "stacked humbucker" I made, and I can
   practically stick this thing on the damn power transformer, and not
   hear any hum.  We're talking VERY quiet.

Sorry, but this won't work.  The pickup output has to do with the number of
turns of the coil, not the impedance.

"Yeah, but the impedance is proportional to the number of turns, isn't it."

Nope, the impedance has to do with the number of turns, the length of each
turn, and the resistance per foot of the wire.  But the resistance per foot
of the wire is hardly accurate to 0.1%.  It's more like 10%.  So it's only
a rough measure of the number of turns.

If you don't believe Maxwell's equations or if you want to try an
experiment; build two coils with the exact same number of turns (say, 7600,
like a Strat).  Wind one with 40 guage wire and wind the other with 42
gauge wire.  Their outputs will be near identical, yet their impedances
will be very different.

  -- Don

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