Fairchild Tables
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 1/3 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
The ordinary shaded-pole motor, which runs your electric drill or power saw, is no good
for such precision work because any variation in the voltage of your house current will
change its speed. Most turntables use a specially designed "induction" motor
which is fairly stable in feed, though extreme changes in line voltage may disturb it
(look for a tag stating its requirements: "95 to 130 Volts" means disaster-proof).
Even this isn't absolutely steady. The 60-cycle alternation of AC electric supply,
however, is invariable (an electric clock practically never goes wrong), and thus a
"synchronous" motor, which decides its speed by the frequency of alternating
current, can keep a constant rpm unless a complete power failure occurs. It also
eliminated the dangers of turntable rumble and extruded "hum." Getting this
constant speed of the motor up to the turntable (in three different varieties) takes
considerable ingenuity. Today's best and most expensive turntables use one of five methods
to translate motor speed into turntable rotation.
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, say, to 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.
Tonearms
A turntable does not become a record player until you add a tone arm, which must be
separately purchased and mounted. Like the custom turntable, the separate tone arm solves
a multitude of problems. You will recall that the cutting stylus rides across the record
on a bar from circumference to spindle, following a true radial path always at right
angles to the line of motion of the groove. For accurate reproduction, the playback
cartridge, too, should always point straight down the groove, so to speak. But we bold the
playback stylus in a tone arm, which pivots, making a curved rather than a straight track
across the record. In a really bad tone arm, the playback stylus will sometimes be off as
much as 10 or 15 degrees. The message of the wiggles is distorted, and the record wears
unevenly and more quickly, as does the stylus itself. This is known as "tracking
error."
Tracking Error
In the old days, before the deep thinkers got at this business, the solution to
tracking error was simply to make the arm longer. A short arm tracks a small circle,
presenting a more steeply curved arc as it crosses the record; a long arm makes a shallow
arc with a closer resemblance to the desired straight line. Then it was discovered that
curving the bead of a fairly short arm, by correct degree, would substantially reduce the
average tracking error over the course of a whole record (Angling the pickup in a straight
arm gives the same geometric effect).
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.
Tracking Weight
The vertical pressure of the playback stylus on the record will be a key factor in both
stylus and record wear, and the various tone arms employ various ways to get the right
"tracking weight." Some use springs at the rear end of the arm. In others the
non-business end will extend some distance beyond the pivot, counterbalancing the weight of
the rest of the arm and the pickup. This means bigger installation space. The GE Baton arm
features a head, attached to the arm itself by a swivel. Most pickups are made to respond
best at a tracking weight of four to eight grams, but the pickups themselves are not all
the same weight. The viscous-damped Gray 108-C adjusts any pickup to four or six grams of
vertical pressure. The GE balancing bar is calibrated and has a moving screw, giving a
choice of tracking weights. Both the spring and the counterbalanced arms often have some
mechanism by which the tracking weight of the stylus can be increased or decreased. But
none of these measurements will do you much good unless you know the actual weight of the
pickup you are using and the weight of the pickup for which this particular arm was
designed. You can measure the final vertical pressure of any arm and pickup on any one of
a dozen gauges --- preferably the Audak ($4), which is most accurate because it is a
balance, with replaceable weights, and has no springs. But even an accurate measurement
(which should be made, with all arms) does not tell you what will happen on warped
records.
Click here for
turntable history page 2.
