In reproducing a phonograph record, the aim is to take out of the groove exactly the intelligence that was pressed into them. And the wiggles in the groove are meaningless in themselves. They have to induce exactly the right physical motion in a stylus before they make sense -- which means that they must move under the stylus at the right speed and that the stylus itself must track the groove accurately, wigwagging as the wiggles demand. A turntable spins the grooves; a tone arm holds pickup and stylus in place. What we want from the turntable sounds simple, but it isn't. In the first place, there are three speeds: 78.26 rpm for the old-fashioned standard shellac records, 45 rpm for the little seven-inchers with the big center holes, and 331/3 rpm for long-playing discs. The speed must be exact in every case. If the turntable is slow, the pitch drops; if fast, the pitch rises.
Moreover, the speed must be exact at every instant of playing. A turntable that alternately slows down and speeds up will ruin musical enjoyment even though its average in each rotation is an exact 78.26, 45 or 33.3 rpm. The phenomenon produced is called "wow," a very expressive word denoting the alternating rise and fall of musical pitch which results from fluctuations in turntable speed. When these fluctuations are rapid, the term is "flutter."
How Turntables Work
On the Rek-O-Kut and the Garrard the power gets to the turntable by means of a "rim drive"; that is, the final agent is a bard-rubber drive wheel which locks into position between the motor's axle spindle and the inside rim of the turntable. This is the most common way of making a turntable spin. Usually the spindle, the upward-protruding end of the motor shaft, is cut in "steps" to three different diameters. The speed-control knob locks the wheel against one of the three steps. When the wheel locks against the part of the shaft with the greatest diameter, the turntable spins most swiftly, and so on. A conical or tapered spindle may be used to give continuously variable speed -- anywhere from 15 to, say, 100 revolutions per minute. There are several variations on this procedure. Rek-O-Kut, for example, locks wheels of different diameter against a one-size spindle; the new Weathers uses a ceramic disc instead of a rubber drive wheel, and attaches the disc directly to the motor shaft. The D & R applies to the drive wheel to the outer rather than the inner rim of the turntable. On the Scott the turntable drive is direct: that is, the drive shaft of the motor locks into one of three gears on another drive shaft, which in turn is geared to the center of the turntable. The Components Corporation uses a linen belt which fits directly onto the drive shaft (at one of three diameters) and then fits around the circumference of the turntable. The Fairchild runs the belt inside, to a cast-iron flywheel below the table. There are arguments for and against each of these methods. The Components Corporation gets the motor farthest from the turntable and the pickup, thus minimizing the danger of noise from the motor. For the same reason, though, it is rather bulky and unattractive, and requires the most elaborate mounting. Direct drive uses metal parts only and can thus be machined to the closest tolerances. It also lasts longest, at least in theory -- but not necessarily in practice. And when something goes wrong, the repair may be expensive. Rim drive requires occasional replacement of the rubber-tired idler wheels and drive spindle-tops. It is, however, the easiest to repair.
Although many hi-fi authorities will still insist on the long arm (which requires a very large installation space), a recent tracking-error test came up with the tiny Ferranti arm as the most accurate tracker in the business. The new Garrard arm may be adjusted to any desired length from 10 to 16 inches, which allows complete flexibility of installation. New ideas include arms which simply hang over the disc; a pickup bug (similar to the bug which holds the cutting stylus) running over the record; and the B-J, a British import, which is really two arms attached to a single pickup and swinging separately so that the pickup is always aligned with the groove.