After Oersted demonstrated that an electric current affected a magnetic compass needle in 1820, Faraday concluded that a magnetic field should be able to produce a current. Faraday demonstrated this in 1831. Over the next century came generators, alternators and finally, someone (Rickenbacker maybe?) applied these principles to a guitar pickup.
A single-coil guitar pickup is just that; a spool of many turns of wire wrapped around a series of magnets. The string moving through the magnetic "field" produces a tiny electrical signal, which can be amplified and processed. Single-coil pickups produce a clear, ringing tone, but are susceptible to outside interference. Humbucking pickups use two coils of wire connected so that the noise will be cancelled or reduced. Humbucking pickups also produce a much stronger electrical signal, and a darker, less clear sound than single-coils.
Most guitars use only one or more pickups with "passive" components such as resistors, capacitors and inductors for tone and volume control.
Active pickup systems include a preamplifier circuit and tone shaping circuitry such as equalizers or even effect processors. The active system consists of transistor or operational amplifiers which require a battery for operation (just like your effects pedals). Active systems provide a much stronger signal to your amplifier and allow greater variation in pickup design and placement.
[This message has been edited by Jon68 (edited 10-12-2000).]
