NAD 5120 Turntable Review

The NAD 5120 combines a semiautomatic, two-speed turntable with a novel “floppy” tone arm; both are designed to provide superior isolation from external shock and spurious vibrations. The platter, a light stamped-aluminum disc, is belt-driven at fixed speeds of 33-1/3 or 45 rpm by a low-speed (360-rpm) synchronous a.c. motor. Speed is changed by a knob on the motorboard that shifts the belt to a different pulley diameter. A thick and unusually heavy rubber mat fits snugly over the platter (the two have a combined weight of 2-1/4 pounds).

The tone arm is a flat, 1/16-inch-thick strip of phenolic material similar to that used for printed-circuit boards. There are elongated slots in the front end for mounting and positioning a cartridge; the other end of the arm carries an adjustable counterweight whose position is shifted (after arm balancing) to provide a calibrated vertical tracking force of up to 3 grams. The tone arm’s internal “wiring” consists of four embedded copper conductors terminating in a four-pin plug that fits a socket in the arm’s support post. Since the arm has no removable headshell, the entire arm is unplugged for cartridge installation and many of the setup adjustments.

The counterweight, in addition to being movable along the axis of the arm by a rack-and-pinion mechanism, is free to pivot vertically to some degree against the force of a compressed spring. This Dynamic Vibration Absorber, or DVA, can be tuned by a screw that varies the spring pressure in order to make the counterweight system resonate out of phase with the main arm/cartridge resonance frequency, thus reducing the amplitude of the resonance. In addition, attached to the counterweight is a small dashpot containing a damping fluid into which a rod connected to the arm system can be lowered by means of a small adjusting screw. This provides a controllable degree of damping of the arm resonance (the amount required depends on the inherent damping in the cartridge/stylus system) that further reduces its amplitude. The arm and platter are rigidly coupled through a mounting plate, with the entire system floated on soft springs attached to the dark-gray, molded-plastic motorboard and base. The resonance frequency of the arm/platter/spring system is below 4 Hz.

Aside from the speed selector and an antiskating dial on the motorboard, the only control on the NAD 5120 is a combination arm-lift and start/stop switch knob on the front edge of the base. It simultaneously turns on the motor and lowers the tone arm or lifts the arm and shuts off the motor. In addition, at the end of a record side the arm lifts and the motor shuts down automatically. The NAD 5120 is supplied with a nearly opaque black, hinged plastic dust cover. The unit is 16-1/2 inches wide, 14 inches deep, and 4-1/8 inches high, and it weighs 11 pounds. Price: $248

Laboratory Measurements

We installed a Shure V15 Type V cartridge in the tone arm of the NAD 5120 for our tests. To perform the full range of necessary setup adjustments requires considerable patience. Although the procedure is not especially difficult, it is cumbersome and time consuming, involving numerous insertions and removals of the plugin arm and observations of the resonance frequency. Fortunately, the detailed instructions include a simplified procedure with tabular and graphic information on almost all cartridge models likely to be used in this arm. This reduces the number of arm-removal operations, but the process is still more involved than the setup for most other record players.

When we balanced the arm as carefully as possible, the calibrations of the tracking-force dial were in error by a not too significant 10 per cent (the actual force being less than the indicated value). The tone-arm tracking error was difficult to measure because of the shape of the arm and the limited visibility of the edge of the cartridge body, but it was less than 0.4 degree per inch over most of the record area and never more than 0.67 degree per inch. (A computer analysis based on the specified arm dimensions confirmed these measurements.)

The playing speeds of the NAD 5120 were very slightly slow, by 0.7 per cent at 33 rpm and 0.2 per cent at 45 rpm. The JIS-weighted rms flutter was 0.08 per cent, and the DIN-weighted peak flutter was ±0.12 per cent, both principally at frequencies below 5 Hz. The unweighted rumble was a very low —42 dB, principally between 20 and 30 Hz. With ARLL weighting, the rumble reading improved to —60 dB.

The tone-arm mass resonated with the VI5 Type V cartridge stylus compliance at 9 Hz. This was measured with the cartridge’s stabilizer disabled in order to make the resonance more visible, but it was still very well damped by the arm’s DVA system. The effective arm mass without the cartridge was about 12 grams. The capacitance to ground of the signal cables and arm wiring was about 175 picofarads per channel. The antiskating dial calibration was quite good, with the optimum setting being about 0.5 gram higher than the tracking-force setting.

The type of suspension system used in the NAD 5120 ordinarily gives exceptional isolation from external vibration. The measured base-conducted vibration isolation of the NAD 5120 was well above average, though it was not quite equal to the results we have obtained from some other turntables using similar suspension systems. The largest transmission mode was at 18 Hz, with a smaller response from 40 to 50 Hz. As usual, the isolation was best when the cover was lowered.

Comment

Like most record players with a soft suspension resonating in the range of a few hertz, the NAD 5120 was well isolated from vibration conducted through its base but very bouncy in its response to normal handling. The stop/play control, unless operated with extreme care, tended to shift the pickup outward, sometimes by a quarter-inch or more. It would be advisable to install this turntable on a rigid shelf or table to minimize jarring effects, but we would expect it to be relatively immune to airborne acoustic feedback.

The setup complexity of the NAD 5120 may be viewed as an asset by some—the perfectionist will be able to trim it as closely as his patience and hearing acuity will allow. And it should not deter others from choosing the turntable if it is otherwise suitable. The benefits, if any, of the full-length setup adjustment (as compared with the tabular “quick setup” procedure) are minuscule. We believe, however, that any degree of reduction in arm-resonance effects obtained by either method is worthwhile.

The question of whether the flat phenolic arm represents an improvement over conventional tubular metal designs is not easy to resolve from our measurements and use tests. Certainly the NAD 5120’s arm has no obvious faults or weaknesses of any kind. (There were, for instance, no significant tone-arm resonances in the audio range of the sort that we have occasionally found in tubular tone arms.) And for those who might want to use different cartridges at different times, NAD sells additional arms for $30, making it easy to change cartridges by merely plugging in a different arm with all the setup adjustments already made.

An interesting side note about the NAD 5120 concerns its source, which is Czechoslovakia. The flat arm was the concept of a Czech audiophile/inventor, and the turntable is manufactured in Czechoslovakia. To our knowledge it is the first hi-fi product from that country to be marketed in the U.S. In any case, like all the other NAD products, the 5120 is an “original,” distinctly different in design from others in the same category and offering features and values not found elsewhere. It is well worth looking at if you are in the market for a new turntable.

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