The Coil of a Guitar Pickup
The coil wound around the bobbin of a guitar pickup consists of several thousand turns of extremely thin wire in one long strand, which begins and ends at points on the base of the pickup where the hook-up wires are attached. The hook-up wires take the electrical signal generated in the coil to the volume and tone controls and, from there, to the output jack.
The coil of any pickup looks much the same to the naked eye — like an elongated spool of thread, consisting of fine wire instead of thread, of course — but differences in its composition and shape lead to differences in the way it performs its job and, therefore, in the way each pickup sounds.
Pickup coils are commonly wound with anywhere from 4,000 to more than 10,000 turns of wire that measures from 0.0025 inch to 0.0020 inch thick (designated as 42 AWG to 44 AWG, using the standard American wire gauge reference system). This wire also has a coating to insulate it so it conducts as one length of wire instead of shorting out against itself.
As simple as a coil may be, several factors in its makeup affect the electrical signal it generates, and, therefore, the sound of your guitar:
The length of wire in the coil: The length, usually indicated as turns or wraps, determines the strength of the signal, in relative terms, with more wire producing a stronger signal.
A bigger coil also produces a signal that tends to distort more easily in the amplifier and has a more prominent midrange tone (in general terms), whereas relatively lower signals from smaller coils stay cleaner and have a tighter low-end and high-end response.
The gauge of wire (its thickness): The wire’s thickness determines how much can fit around any bobbin and therefore plays a part in shaping its sound.
The shape and proportion of the coil: Tall, narrow coils sound brighter and more focused (in general), and wider coils sound deeper and fuller.