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Dummy coils

4/17/1997 3:47 PM
Mark Hammer
Dummy coils
This is about dummy coils.  
They were popular with high-enders for a while,but then fell out of favour. Still, they're worth mentioning once in a while to those who never knew about them or simply forgot.  
Guitar pickups are, at one in the same time, both electromagnetic microphones and antennas. The mic picks up the string vibrations, and the antenna picks up hum, radio waves, and other goodies.  
If one has a guitar pickup coil, but without the magnet, what's left is the antenna part without the mic part. Some guitar companies (and I'm thinking here of Alembic) used to manufacture instruments with "dummy coils" installed either under the pickguard or in the centre-position.  
What good is a pickup that only picks up radio waves and hum, you ask? Well, if we wire up that coil out of phase with a real pickup, what each of those respective "antennas" picks up gets cancelled. Since the dummy coil has no magnets, we don't have to be concerned with magnet polarity either.  
Okay, why is this of use to YOU, the discriminating consumer? Do you have a lousy old pickup with a ceramic magnet glued to it sitting around the house? Pop off the magnet, wire up the pickup out of phase with your existing pickups, stick the dummy coil in the control cavity, and voila! all your pickups are now humbuckers.  
This mod is especially useful for Telecaster players. I stuck a dummy coil in a friend's control cavity and the reduction in hum was noticeable. The nice thing is that since the dummy coil isn't being used to pick up string vibrations, it doesn't really matter where you put it that much. Even if you stick it under the metal control plate on a Tele, Mustang or Jaguar, (presumably shielding it from RF and hum) it is still able to "pick up" some radio and hum and cancel it out with what the pickups themselves get.  
As with humbucking pickups per se, the better the match in terms of number of turns (to one's existing pickups), the better the hum rejection. However, you can still get some reasonable hum-rejection by removing the magnets from a sleezy 4500 turn Japanese pickup and tucking it away.  
Wiring up the dummy coil simply involves connecting it to the hot/input and ground lugs on your volume control so that it is always "on". Since it is only one coil, switching all other pickups on (2 on a Tele, 3 on a Strat)will result in somewhat less hum-rejection because you've got one antenna competing against more than one, but it won't harm tone or the guitar.  
Is this better than replacing all your single-coils with humbuckers? Not necessarily, but if you like your guitar's tone the way it is, but don't like the hum/noise, this can help.
4/18/1997 10:33 AM
Jeremy Epstein

Mark, thanks for your informative post. I'd just like to add that they're essential for nailing the "Mortimer Snerd at the El Mocambo" sound.  
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