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Pickups: Turning Movement into Voltage

The magnet-and-coil trick behind every electric guitar, why single coils hum, and what a humbucker does about it.

A pickup is a magnet with a coil of wire wrapped around it, and that is genuinely the whole idea.

The magnet sits under the strings, close enough that it magnetises the short section of steel string above it. When you pluck, that magnetised piece of string moves. A moving magnetic field induces a voltage in any nearby coil of wire — this is electromagnetic induction, the same principle behind every generator. The string's movement becomes a tiny alternating voltage in the coil, oscillating at exactly the frequency the string is vibrating.

The coil is not a few loops. It is typically five to eight thousand turns of copper wire about the thickness of a human hair, because the more turns, the more voltage you get. Even so the output is small, a fraction of a volt, which is the amplifier's problem to solve.

A bare single-coil guitar pickup removed from a guitar, showing six metal pole pieces in a row through a flat bobbin with copper wire wound around it and two lead wires
A single-coil pickup with its cover off. Six magnetic pole pieces, one per string, standing through a bobbin wound with fine copper wire. The two wires at the top carry the signal out. Photo: Coveyj, CC BY-SA 3.0

This was not obvious in advance, and it took a while to get right. The first commercially successful electric instrument was Rickenbacker's cast-aluminium lap steel of 1932, nicknamed the Frying Pan for its shape, with a pickup built from a pair of horseshoe magnets straddling the strings.

An aluminium Rickenbacker Frying Pan lap steel guitar from 1934 displayed in a museum case, with a small round body and a long neck
A 1934 Frying Pan. Not a guitar you would recognise as one, but the first electric instrument that sold. Photo: doryfour, CC BY-SA 2.0
A 1937 United States patent diagram titled Electrical Stringed Musical Instrument, showing side and cross-section drawings of a round-bodied lap steel guitar with a horseshoe magnet pickup over the strings
The patent, filed by George Beauchamp in 1934 and granted in 1937. The cross-section at the top right shows the horseshoe magnets arching over the strings with the coil beneath — a magnet, a coil, and six strings passing through the field. Diagram: George D. Beauchamp, US Patent 2,089,171 (public domain)

Single-coil pickups sound bright, clear and immediate. They also hum. A coil of thousands of turns of wire is an excellent antenna, and it picks up the electromagnetic field radiating from mains wiring, transformers, fluorescent lights and computer screens as a steady buzz at 50 or 60 cycles per second.

Seth Lover at Gibson solved this in 1955 with a genuinely elegant trick. Use two coils instead of one. Wind the second coil in the opposite direction and flip its magnet's polarity. Hum arrives at both coils identically, so wiring them together in series makes the hum cancel out. The string signal, however, is reversed twice over — once by the winding direction, once by the magnetic polarity — so it adds up instead. Hum gone, signal doubled.

An uncovered humbucking pickup showing two coils side by side, one row with six slot-head screw pole pieces and the other with six smooth metal slugs
A humbucker with its cover removed: two coils side by side, one with adjustable screw poles and one with fixed slugs. That is the hum-cancelling pair. Photo: Stratocaster27, CC BY-SA 4.0
The underside of a vintage Gibson humbucking pickup, showing a metal baseplate, mounting legs and a small black sticker reading Patent Applied For
The same pickup from below. Gibson put a small Patent Applied For sticker on these between roughly 1957 and 1962, which is why collectors call the originals PAFs. Photo: Stratocaster27, CC BY-SA 4.0

A humbucker's two coils sit slightly apart and sense a longer stretch of string, which averages out some of the high harmonics. That is why humbuckers sound thicker, warmer and louder while single coils sound brighter and more cutting. Neither is more correct. Gibson also makes a third thing, the P-90 — a single coil, but a wide, flat one with a different magnet arrangement, which lands somewhere between the two.

A cream-coloured Gibson P-90 pickup with a chrome dog-ear mounting bracket, mounted on a red guitar under the strings
A P-90 in a dog-ear mount. Introduced in 1946, and still the sound of a lot of raw, gritty rock and roll. Photo: Maxo / Bubba73, CC BY-SA 2.5

Where a pickup sits matters as much as how it is built. A string barely moves near the bridge and swings widest near the middle of its length, and the pickup only hears the movement directly above it. So a bridge pickup gets a small, harmonically rich signal — bright, cutting, good for rhythm and bite — while a neck pickup gets a bigger, rounder one, which is why lead players reach for it.

Three white single-coil pickups mounted in a row under the strings of an electric guitar on a tortoiseshell pickguard
Three pickups in the three classic positions: neck, middle and bridge. Same pickups, three different views of the same string. Photo via Wikimedia Commons, CC BY-SA 3.0

Play over this and switch positions as you go, if your guitar has more than one pickup. Play the same phrase at the neck and then at the bridge and you will hear the difference far better than any description of it.

Highway Soul | Groovy Classic Rock Backing Track in C Major | BT 718
Backing Tracks Center#rock#Cmajor

A classic rock groove in C. Try a rhythm part on the bridge pickup, then the same thing on the neck.