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.

There was one drawback to this design. The bar magnet used was nonadjustable. Correcting string imbalances required filing down the portion of the magnet underneath the strings which were too loud. The next development would be "pole pieces" for each string.

By now there were several competing pickup designs. On a Fender pickup, these pieces were actual magnets which were set for height at the factory and then sealed, while a Gibson "Standard" used six adjustable screws set into a bar magnet. Mounted on the new solid-body guitars, the sound from these pickups could now be amplified to the point that the noise and hum they generated became a real problem. Obviously, a pickup was needed which would suppress this interference.

Such a pickup began appearing on Gibson guitars in the late 50's. Designed by Mr. Seth Lover, the* Gibson humbucker used two coils wound in opposite directions, with reversed polarity, so that the hum generated by one coil would be cancelled by the hum of the other. The warm response and high output of these pickups made them immensely popular among rock "n" rollers. In time, this sound came to be the trademark of Gibson guitars, while the Fender sound meant the clear ring of the single-coil pickup, even though Gibson continued to make the "Standard" and Fender was to develop a humbucking pickup.

Each design has its admirers and its detractors, and a day spent in any guitar repair shop will show you the advantages and disadvantages of each. Fender guitars are often criticized for thin sound and lack of sustain, since their pickups cannot be moved close to the strings. Each pole piece is a magnet, remember, and the closer it gets to the string, the more it "pulls" on the string. If it is moved too close, the pickup will cause the guitar to sound out of tune. DiMarzio also has a line of Fender replacements, the most recent additions being the SDS-1 Strat replacements and the P-Bass pickup. Both feature adjustable pole pieces set into a bar magnet, as in the Gibson "Stan. dard." This allows the pickup to be adjusted closer to the strings without pulling on them. DiMarzio pickups are offered as featured equipment on many new guitars, and the list of professional musicians using these pickups is endless.

By comparison to a single-coil, humbucking pickups sound muddy and distorted, since their design sacrifices some highs to get the humbucking effect. Guitars equipped with these pickups are faulted for being "onesound" instruments.

At Strings and Things, I hear these questions daily: "How do I get my Strat/Les Paul to sound more like aLes Paul/Strat?" "My Strat/Paul sounds weak. Can I get more punch from it?" Here in Memphis, the sound and appearance of "patent-applied for" humbuckers and pre-CBS (pre-"66) Fender pickups are highly prized. Such pickups are scarce, however, and costly when they can be found.

Apparently a similar situation exists in shops nationwide, since the last few years have seen enormous changes in the market for replacement and specialty pickups. Once a guitarist was limited to three or four choices; now there are at least a dozen manufacturers with several different models of humbucking and Fender replacements competing for a place on his axe.

Far and away the most requested replacement pickups are those made by DiMarzio, and the most popular pickups in this line are their humbucking replacements. A variety of humbuckers are available, ranging from the PAF, designed to match the performance of patent-applied for Gibson humbuckers, through the high-output Super Distortion to the Dual Sound humbucker, a specialty pickup offering the guitarist a choice between humbucking sound and one similar to the Fender Sound.

Perhaps the hottest replacement pickups now available for Fender; guitars and basses are made by Schecter Guitar Research. Increasing the diameter of the pole piece magnets to V4" in addition to wrapping more wire on the coil gives these pickups more punch and sustain without sacrificing the brilliant Fender sound. Tapping the coil in two places allows the guitarist to change from a warm, high-output mode to one matching the performance of the pre-CBS Fender pickups. These double-tapped pickups are available separately or mounted on a pre-wired pickguard assembly. They are ideal for the Fender owner seeking a more versatile instrument, but not wanting to alter his axe's appearance or to lose the original sound.

For the guitarist looking for a wide range of sounds, there is the "Beast" humbucking replacement. Such a pickup offers many different wiring combinations when used in conjunction with a rotary switch. This is one of several replacements as available for Fender and Gibson guitars from Bartolini Hi-A. Extremely clean as well as high-output, their bass pickups are in demand throughout the country.

A unique pickup is available from Lawrence Sound Research, namely an exact replacement for Fender Strats and Teles that is a true humbucking pickup. By standing the coils on edge and sandwiching a bar magnet between them, this pickup achieves a hum-cancelling effect without losing the Fender sound. Lawrence humbuckers are also unique, since they use bar magnets rather than pole pieces. Careful calibration of these pickups at the factory assures a balanced sound and negligible string pull from this design.

This is not to say that the above mentioned are the last words on pickups; User demands means this market is changing daily, and new designs are constantly cropping up. I regret that space limitations left several names unnamed and facts unmentionea. Those seeking more information on how pickups work or on the history of electric guitars can refer to Tom Wheeler's The Guitar Book (Harper and Row, New York) or Donald Brosnac's The Electric Guitar (Panjadrum Press, San Francisco).