AR Turntable Review

About a quarter of a century ago, Acoustic Research developed a turntable whose simplicity, outstanding performance, and low price earned it a unique place in the hi-fi marketplace—and something close to classic status among knowledgeable phonophiles. Aware of the degradation of sound quality caused by acoustic feedback, AR’s founder, Edgar Villchur, designed a turntable (actually a complete record player, since it was available only with an AR tone arm) that was virtually immune to external mechanical excitation.

In addition, the AR turntable essentially eliminated audible rumble by using a very small, low-torque twenty-four-pole a.c. motor (similar to those in electric clocks), which turned at only 300 rpm instead of the 1,800 rpm of the four-pole induction or synchronous motors commonly used at the time. The motor’s fundamental vibration frequency was thus lowered from the very audible 30 Hz of the higher-speed motors to an inaudible 5 Hz. Since the torque of the AR turntable’s motor was relatively low, its platter mass was kept correspondingly small, and it was driven via a light rubber belt. Speeds were changed (between 33-1/3 and 45 rpm) by removing the platter and manually shifting the belt to a different-diameter pulley.

The original AR turntable was upgraded several times before being withdrawn from the market a few years ago, but there has evidently been sufficient demand to warrant designing and manufacturing a new model with the same basic virtues. The new AR turntable that we tested for this report is, in many important respects, almost identical to its respected ancestor. Its styling is much handsomer, however, and it is available either with an AR tone arm or with a “blank” mounting board that can accommodate any of a number of high-quality tone arms from other manufacturers. This option disposes of one of the more persistent and valid criticisms of the earlier model, which paired a superb turntable with a rather old-fashioned and hard-to-replace tone arm.

The key to the remarkable acoustic isolation of both the old and new AR turntables is the rigid coupling of the tone arm to the platter by a T-shaped cast-metal plate. This entire arm-and-platter assembly is then suspended on damped springs from the turntable’s motorboard and base. The extremely soft three-point suspension (we would estimate its resonant frequency as about 2 or 3 Hz) makes it possible for the base or dust cover to vibrate with rather large amplitudes at audio and infrasonic frequencies without transmitting this motion to the arm or platter. And even if the arm and platter do move as a result of external vibration, they do so as a single unit and therefore do not affect the output from the cartridge.

The cast-aluminum outer platter of the AR turntable weighs about 2-1/2 pounds, and the total weight of the platter is given as 3.9 pounds in the specifications. The record mat is a thin disc of felt-like material. The new AR tone arm is a straight tubular design with a low-mass removable headshell. The counterweight, which is moved from a balanced condition to set the tracking force, carries a scale calibrated from 0 to 3 grams in steps of 0.5 gram. A similarly calibrated antiskating dial is mounted on the arm base near the arm-lift (cueing) lever, the downward action of which is viscous damped. Attached to the arm base is a clip that serves as an arm rest or retainer.

The base of the AR turntable is made of oiled walnut and is supported on small rubber feet (which do not serve any isolating function and merely protect the supporting surface). A rocker switch on the top of the base controls the power to the motor, and a small pilot light on the front surface glows when it is on. A hinged clear-plastic dust cover remains open when fully raised (but not at intermediate angles). The turntable’s dimensions are 18-3/16 inches wide, 15-1/4 inches deep, and 7 inches high with the cover closed (a 17-inch vertical clearance is needed to open the cover). It weighs 18 pounds. Price: with the AR tone arm, $429.99; without the arm (but including a blank tone-arm mounting plate), $299.99.

Laboratory Measurements

We installed a Shure V15 Type V cartridge in the AR tone arm for our tests. The measured capacitance of the arm and signal-cable wiring was about 80 picofarads per channel (the nominal rating is 85 pF) with a very low interchannel capacitance of 2 pF. We set the stylus overhang with the aid of the plastic jig furnished with the turntable, and the resulting tracking error was less than 0.33 degree per inch (barely measurable). After the arm was balanced, the actual vertical tracking force was about 0.1 gram higher than the scale setting (this is a function of how accurately the arm is balanced when the player is first set up).

The effective arm mass (exclusive of the cartridge) was a relatively low 9 grams. It is rated at 13 grams, but different measuring techniques can easily account for the difference. With the rather compliant VI5 cartridge the arm system resonated at an ideal frequency, 10 Hz. The antiskating dial had to be set about 0.5 gram higher than the tracking force for optimum correction. Because of the floating suspension, considerable care was necessary to avoid jarring the arm when using the cueing lever, but after some practice we were able to use it effectively. The antiskating torque caused about 5 seconds of a record to be repeated each time the arm was lowered, and the descent took 4 to 5 seconds.

The turntable speed was about 0.3 per cent fast, and its flutter was a very low 0.055 per cent weighted rms (JIS) or ±0.08 per cent weighted peak (DIN). The measured flutter was largely a result of test-record eccentricities, and its components were principally below 10 Hz. As with the original AR turntable, rumble was very low, measuring —40 dB unweighted ( — 46 dB in the lateral plane) and —64 dB with ARLL weighting. The rumble had a broad, random frequency spectrum, and the measurement may have been limited by our particular test setup and the inherent rumble of our silent-groove test records.

Comment

Anyone who saw the old AR turntable being demonstrated cannot forget how it could be pounded with a hammer (actually, a soft mallet) without skipping or even adding an audible thump to the music. The new AR turntable is, if anything, even better than the old one in this respect. We were able to strike it as hard as we wished with a fist or open palm with absolutely no audible effect on the program. The isolation system should make the turntable highly resistant to base-conducted vibration, and we expected it to excel in this test. Even so, we were not prepared for a measured immunity to external vibration that was 20 to 40 dB better than' that of any other turntable we have tested in the past couple of years. (Because of changes in our test setup, a close comparison to still earlier units is not feasible.) It is safe to say that the new AR turntable is, by a comfortable margin, the best-isolated record player we have ever used or tested. The only significant transmission took place below 20 Hz, with a minor response at 50 Hz. Anyone who has had problems with acoustic feedback need look no further than the new AR turntable for a solution.

As we noted earlier, one of the few valid criticisms of the old AR turntable concerned the tone arm it included, which was lacking in refinement even by the standards of that time. The tone arm available with the new AR turntable is a very good one that is thoroughly compatible with the turntable and with almost any cartridge one might wish to use. For more demanding audiophiles, however, the blank-mounting-board option permits using the turntable with almost any other arm available.

Our only criticism of the new AR turntable concerns the considerable delicacy needed to handle its arm-cueing lever and the fact that the arm rest lacks any locking device. It is only too easy to knock the arm from its rest clip accidentally, and in the interest of stylus longevity we soon developed the habit of keeping the lift lever up at all times when not playing a record.

The new AR turntable appeals powerfully to our sense of good design. It is almost purely functional yet very attractively and tastefully styled. A simpler record player could hardly be imagined, and, like its predecessor, it should give many years of service with no more maintenance than a periodic belt replacement. And in terms of acoustic isolation, even pounding the base with a hammer (not really a recommended practice, of course) is unlikely to do more than mar the handsome finish.

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