Fig. 5 — Photo courtesy of Seymour Duncan

The Coil
A coil, which typically surrounds the poles or the magnet, usually comprises 5,000 to 9,000 turns of super-fine copper wire. Fig. 5 shows the coil on a modern Strat-style pickup made by Seymour Duncan. Current manufacturing techniques automate the winding process, ensuring that the wraps are laid down evenly, and that the pickups coming out of the factory will sound identical. Pickups made in past decades were wound by hand, which meant less consistency in the number of windings and the evenness by which they were coiled. (Pickups made by hand today are similarly more variable, at least in some respects.) Does this inconsistency contribute to a more classic sound? It’s likely, since it’s more true to the winding techniques of the past. Is that sound any better or worse? It’s a lot like drinking wine: The best wine is the wine you like the best.

Like windings in a speaker or an electric motor, the coil wire is covered with a clear coat of insulation—otherwise it would just short out. That coating can be enamel, Polysol, or Formvar. The coatings themselves have no direct effect on a pickup’s sound, but the coating’s thickness can. Fender used Formvar back in the day, although its formulation has changed over the years, and some folks love to debate whether these changes produce sonic differences.

When you see a measure of a pickup’s resistance, it’s a measure of the coil. It’s a factor that may receive a bit too much importance—there’s a lot more to consider. To be accurate, we should technically be discussing impedance, which refers to the ability of an AC signal (your guitar sound) to get through, as opposed to resistance, which is the measurement for DC. The important difference is that the coil’s impedance will vary with the signal’s frequency. Because resistance is much easier to measure using a simple multimeter, that’s what you commonly see in pickup specs.

In pickups, copper wire gauges—running thinner to thicker—are typically 44, 43, or 42. Thinner wire means increased resistance. To use a water pipe analogy, a thinner pipe requires more water pressure. With the same number of windings, thinner wire will result in a smaller coil. The smaller diameter of 44-gauge wire translates to 36 percent less copper per inch than 42 gauge. Tone-wise, thinner wire is generally more mid-centric, and high and low frequencies are not as prominent.

Alnico 5 is stronger than alnico 2—as the numbers increase,
so does magnetic strength.

Increasing the number of windings results in a hotter (i.e., louder) pickup. Therefore guitarists often request overwound pickups, which have a higher resistance measurement. But it’s a misconception that hotter pickups, or pickups with higher resistance, are necessarily more desirable than those with a lower resistance. Curtis Novak is among those pickup makers who play down the importance of resistance as a meaningful measure of performance. “Younger musicians will typically look for the hottest, loudest pickup,” he says. “As players get older, they get more into the nuances. You’d think older guitarists’ hearing would be degraded by many years of playing, but it’s the opposite—they’re more concerned with fidelity and intonation.”

But be prepared, increased fidelity will also result in a pickup that’s less forgiving—you have to play more carefully. String-to-string separation will be clearer, but mistakes will also be more readily revealed. After trying what Novak considers to be his best-sounding pickup model, guitarists often tell him, “I feel like I have to work harder on my technique.”

The bottom line: If you’re thinking about swapping pickups in your guitar, it’s more useful to discuss the sound you’re looking for with a pickup maker, as opposed to requesting a certain resistance or other technical specification.

The Bobbin
On some pickup designs, the coil is created by wrapping the wire around a bobbin—a separate oblong part that is then positioned to place the magnetic poles in the coil’s center. Pickups with adjustable steel screw poles typically use this configuration. Other pickups forgo the bobbin—the wire on Stratocaster and Telecaster pickups is coiled directly onto the magnetic poles. Without a bobbin, the pickup can be smaller. Sound is also influenced because lack of a bobbin brings the coil wire as close as possible to the magnet, strengthening the signal that the coil picks up.

There are other non-bobbin designs. For example, a Danelectro “lipstick” pickup wraps the coil directly around a bar magnet, allowing both to fit within a small, cylindrical metal cover while keeping the number of parts to a bare minimum.

Fig. 6 — Photo by Dan Formosa

Magnet Position and the Magnetic Field
Looking at the pickup poles, one might easily assume where the magnetic field is located—directly above each pole. But it’s not that simple. Other metal in the pickup, and the location of the magnet itself, influences the size, shape, and position of the magnetic field. A pickup’s design that places the magnet within a metal C-channel extends the magnetic field to the edges of the channel. As described in a 1966 patent, one of Leo Fender’s pickup designs goes further by calling for metal “teeth”—formed by notches in the channel—on either side of each of the six poles to further control the area of magnetic force (Fig. 6).

Other pickups using adjustable steel poles locate their bar magnets directly beneath the poles. Simple; it just adds height. As an alternative, Ralph Keller’s 1954 design for Valco pickups places the magnet to the side of the coil and steel poles (Fig. 7).

Fig. 7 — Photo by Dan Formosa

A similar configuration is used in the Hilo’Tron pickup from Gretsch. While the original Hilo’Tron included adjustable poles, it unfortunately didn’t provide for an easy way to raise the pickup body. Which is too bad, because bringing the magnet itself closer to the strings makes a world of difference. Proper adjustment on that pickup requires shimming the entire assembly to raise the pickup in a trial-and-error manner—difficult but worth it.