Pinched Coil Problem - Common Recurring Failure in Single Coil Pickups

Gutiarsmith Richard Stanley says: Pinched coil are the most obvious recurring failure mode in single coil pickups. It's not a factor in humbuckers because their construction is different. Pickup wire it's called copper magnet wire looks like bare wire, but it has insulation on it or it would be useless for a pickup. The wire typically is in the range of 0.002" diameter, so it pretty delicate stuff. And the insulation coating is barely tens of thousandths of an inch thick. So there's not much there. When you build a pickup, the wire has to be handled in a way that doesn't jeopardize it. The insulation can easily be scraped off in the process of winding, resulting in shorted turns. It must be wound on the pickup frame very carefully. All of the wire guides and the tensioning system that the wire passes through must have perfectly clean and smooth surfaces.

It's easy to see how vulnerable the wire is and the magnets go through the bobbin flanges, the wire is packed in there pretty tight in those corners. As the pickup rotates on the winder it puts a lot of pressure on the ends. Many single coil pickups still use cardboard bobbin flanges which can move and flex and they typically aren't glued to the magnets. So what happens is with a little bit of flexing, the pickup wire can get pinched between bobbin and the magnet. And that causes electrical continuity with the magnet. It still sounds totally normal, but the signal-to-noise ratio will be worse than what single coil pickups usually are anyway. God knows they're noisy anyway! Then, more often than not, sooner or later, the wire that's pinched in there, breaks, and at that point you have an open circuited coil resulting in reduced volume and almost no bass response. If the break is near the grounded end of the coil, the volume won't change much, but you'll lose all the bass. It starts to sound like the worst, tinniest sounding pickup you ever heard. And the way you detect pinched coil is to take an ohm meter and check from the terminals to the magnets on the high range of the meter, and if you see continuity anywhere between the wire and any of the magnets, you know it's pinched. 

I actually see quite a few bad out-of-the-box aftermarket single coil pickups with pinched coils. And it's mainly because they aren't put together properly with adequate protection. When players bring me pickups to install, the first thing I do is check them, and I tell them, if you own an ohm meter, check them yourself. Take the meter to the store and try it, because you will run into it. I found through my client's pickups one high profile manufacturer that routinely turns out pickups that have pinched coil right out-of-the-box. My client got a replacement set for the first set that were bad, and the second set was bad too. The company said: "That can't be — we lacquer the magnets so that can't happen." Well in the first year I was doing pickups, I learned what happens when you lacquer the bobbin and magnets. Some of the solvents that are in lacquers are also common to the insulation on the wire. So if you lacquer the magnets, then put the wire directly on the magnets, when you wax dip it, it heats up the lacquer, and the lacquer off-gasses some of the solvents, and it melts that really thin insulation off the wire. You wind up not only with pinched coils and wire that is in continuity with one or more of the magnets not even just the end magnets but you wind up with shorted turns also.