Ace Frehley. Joe Walsh. Eric Clapton. Three electric guitarists. Their sound depends not so much on wood as it does on bar magnets and copper coils. We are talking about guitar pickups, the component that makes the guitar electric.

The first electric instruments began appearing in the 1920's. Early electric guitars were acoustic instruments with a contact microphone mounted on the guitar's body. While this gave a guitarist the volume needed to be heard over a big band, it also amplified any noises made by striking the instrument and sometimes nearby conversations.

The first pickup designed specifically for guitars was the "Charlie Christian" pickup used on early Gibson electrics. Named for the revolutionary jazz guitarist who helped popularize the electric guitar, this pickup was a cobalt magnet wrapped with copper wire and placed under the strings. Vibrations from the strings would cause changes in the magnetic field generated by the pickup. These changes resulted in electronic vibrations which, after being sent through an amplifier, caused a speaker to move, thereby reproducing the guitar's sound.

When not thinking up ideas for his column, Jim Lillard can be found at Strings And Things in Memphis.