Welcome to Jim Miller's Guitar Question of the Month. Jim Miller also authors Tech Notes Online, a weekly Sweetwater column covering all aspects of today's music, from stage to studio.
Q: "How does a guitar pickup work?"
A: Hmm, well you can get the quick and easy explanation (for all you "normal people" out there) or the complex explanation that involves acoustics, electronics and the laws of physics (which would be great for all us "techies"), but I'll try to give an answer that is fairly complete without getting into the minute details.
Obviously, any electric guitar is fitted with some type of pickup so that the instrument can be amplified. From the earliest ceramic pickups to today's most sophisticated units, they are all positioned under the metal strings of the guitar (or bass guitar) where they generate a magnetic field.
When the strings are plucked, the magnetic field is disturbed, causing pulses of electrical energy within the coils (the fine copper wire that is wound hundreds of times around a bar magnet). These are typically very low voltage, so an amplifier is required to "magnify" the sound and then send it out via a speaker (or set of speakers).
These days, most pickup designs are either single coil or twin coil (dubbed the "humbucker" by Gibson). The stronger the magnet and the more windings you have of the copper wire, the louder the signal becomes. When the signal becomes too "hot" - that is, when it generates a very high output - distortion can result. Early on, guitar manufacturers worked hard to eliminate this, but by the 1960s, guitar players realized that some amount of distortion could be quite pleasing.
Most Fender guitars were originally designed with single coil pickups, which resulted in the crisp, bright sound we first heard in the classic "surf music" of the early 1960s. Both the Fender Telecaster and Stratocaster were equipped with these single coil pickups, though modern versions of both are available with humbuckers. Many other manufacturers now offer either or both types of pickups in their various models.
The first Gibson humbucker was engineered in the mid-1950s, mainly to overcome the problems of electrical interference or hum. So this new pickup "bucked the hum" (see WFTD Humbucking) - get it? This was accomplished by using two coils instead of one, and these were wired in series so that the electrical current flows from one coil to the next, but the second coil was wound in reverse (also known as "out of phase") so that the annoying noise could be (in theory, at least) cancelled out.
Humbuckers generally produce a fatter, warmer sound, but by the late 1970s, manufacturers realized that musicians wanted both kinds of sound - crisp and bright along with fat and warm - and so they developed ways to split the coils, also known as "coil tapping."
To balance the relative volumes of the individual strings, most pickups have pole-piece that are either fixed in position a certain distance from the string, while others can be raised or lowered to keep the volume consistent. Some modern pickups designs are sophisticated enough to balance the level of each string without requiring pole-pieces (for example, the popular Fender Lace Sensor pickups which were fitted into certain Strat models starting in the 1980s).
For amplifying acoustic guitars, standard pickups were often installed in the soundhole, though today, acoustics are most often fitted with a piezoelectric pickup in the bridge, which use special crystals (that were originally discovered in the 1880s) that generate an electrical current when mechanically stimulated. Such stimulation occurs when the strings are plucked, thereby causing the top of the guitar to physically vibrate or resonate. We will discuss piezos in depth in a future column.
