Dual Redesigns A "Classic"
Dual CS-7310 automatic single-play, direct-drive turntable, with integral base and dust cover. Dimensions: 16 1/2 by 14 1/2 inches; 5 inches high with cover closed, 10 inches additional height and 1 Inch at back required to open cover. Price: $559; with optional Ortofon ULM-60E pickup, $699.95. Warranty: "limited," two years parts and labor; ninety days for cartridge body. Manufacturer: Dual, West Germany; U.S. distributor: United Audio, 120 S. Columbus Ave., Mount Vernon, N.Y. 10553.
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Dual CS-7310 turntable
SPEED ACCURACY (at 33 or 45 rpm) no measurable error at 105, 120, or 127 VAC
SPEED ADJUSTMENT RANGE at 33 at 45
-6.6 to +6.0%
- 6.8 to +5.9%
WOW & FLUTTER (ANSI/IEEE weighted peak)
± 0.04% average; ± 0.07% max. instantaneous
TOTAL AUDIBLE RUMBLE (ARLO -63 dB TONEARM RESONANCE)
DAMPING (set at 8.5 see text) with Shure V-15 Type III pickup vertical 8.4 Hz; 2-dB rise lateral 5.2 Hz; 4-dB rise with Ortofon ULM-60E pickup vertical 9.3 Hz; 5.4-dB rise lateral 8.3 Hz; 6) 6-dB rise
ARM FRICTION negligible MIN.
STYLUS FORCE FOR AUTO TRIP 210 mg
TOTAL LEAD CAPACITANCE 208.5 pF
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The CS-7310 is the latest incarnation of what has come to be a classic Dual: the Model 701 (HF test reports, March and September 1974), its first non-changer in this country and the first to incorporate a mechanical anti-resonance filter in the counterweight assembly. The 731's fully automatic, single –play mechanism is virtually foolproof, and the ULM (ultralow mass) tonearm in conjunction with a specially designed Ortofon low-mass pickup is a study in careful, synergistic engineering. Each of the nine turntables, including the changers, in the Dual line incorporates the ULM tonearm and can be ordered with a ULM pickup (2.5 grams). When so mated, the total effective mass of the arm and cartridge is a featherweight 8 grams.
To effect such a dramatic lowering of mass, Dual re-engineered its familiar straight tubular arm, shaving down its diameter, reducing the size and mass of the offset headshell (or, more properly, clip-in mounting platform), and lightening the counterweight. Balancing the arm with cartridges weighing up to 4 grams should be no problem; extra weights are provided for heavier pickups. The company retained the gimbal-suspension principle, but in a strikingly attractive redesign. And it refined the resonance damping of the counterweight so that you can adjust antiresonance behavior to the pickup in use. The "gauge" is marked in increments from 5.5 to 10; you set the filter index after consulting a graph in the owner's manual, showing correct values according to the weight and compliance of a pickup, where known. Data for severs' popular pickups are included, and such figures for most other cartridges are available from their manufacturers.
Power is provided by a direct-drive motor whose speed is monitored and corrected via a quartz-crystal phase-locked loop circuit. A knurled knob at the left of the platter selects either 33 or 45 rpm, and the speed adjustments (actually for deliberate mis-adjustments) can be defeated by a switch between the two verniers. There are two speed indicators; strobe markings cast into the platter allow for constant monitoring, and departures from dead-on speed read out on an illuminated front-panel display as positive or negative percentages vs. the quartz reference-up to 5 1/2% fast or slow.
The automatic mechanism seems as jam-proof as any we've encountered. A knob to the right of the platter can be set for single play or for constant replay. The cueing lever on the top deck is duplicated by the LIFT button on the front panel. Both cueing speed and tonearm cueing height are easily adjustable--the latter at a screw next to the platter, behind the "headshell" in our picture. For automatic play, a touch of the START button is enough to set things in gear; for semiautomatic operation, moving the tonearm away from its rest automatically starts the platter rotation, while pressing STOP or returning the arm to its rest will stop the play cycle.
Data from CBS Technology Center show the CS-7310 to be deserving of its flagship status in the Dual line. Air its measurements put it firmly in the excellent category. Accuracy for both rotation speeds remains exact and unvarying at each of our line voltages. Speed adjustment range, even greater than the 11% claimed by Dual, allows for a full half-tone pitch change in either direction from normal. Both average and instantaneous flutter values are impressively low, and total audible rumble is in line with that of other top-quality turntables. No measurable error could be found in the settings for vertical tracking force, which is calibrated to 2 grams with 0.1-gram resolution. Antiskating bias, dialed in on a triple scale (for spherical, elliptical, and CD-4 styli), is applied quite linearly and falls within theoretically desirable values. The force needed to trip tonearm return at the leadout groove is well below the normal vertical tracking force range.
The lab measurements for tonearm resonance, including the effectiveness of the tunable antiresonance filter, encompassed both the values obtained with our "standard" Shure V-15 Type III pickup and those for the premounted Ortofon ULM-60E. With the Ortofon pickup and the filter set at its locked (presumably inoperative) position, tonearm resonance falls just a hair short of the "ideal" 10 Hz. Setting the filter to the cartridge's recommended 7.8 index point results in a small (about 1/4 dB) diminution of the vertical resonance amplitude plus a 1-dB improvement in the lateral plane-not a very dramatic effect, but since the resonance already occurs in the preferred frequency range, there's no cause for complaint. The more massive Shure's resonance falls, predictably, a little closer to the area where warp information might be transmitted to the amplifier: above 8 Hz in the important vertical plane, but around 5 Hz horizontally. Strangely enough, the lab found that the excellent (2-dB) amplitude of the vertical resonance actually increased to 4 1/4 dB when the filter was moved from the locked position to the Shure's recommended index point (7.0). The best results with both pickups were found with the filter moved to about 8.5 and are shown in the data; the filter affects the resonance amplitudes, not their frequencies.
In use, and navigating the worst warps we could find, the Dual/ Ortofon combination proved very agile indeed, with nary a mistrack. Even when we investigated the ability of the suspension system to isolate the pickup from shocks to the base and the surface on which it stands--a test in which we judged the results no better than average--the pickup refused to leave the groove. So, while the lab measurements on the antiresonance filter fail to document much advantage in what strikes us as an excellent idea, the actual behavior of the arm with its "matched" cartridge is exemplary. So is that of the automatic cueing and repeat features, which we consider a joy to use.
(High Fidelity, Jan. 1980)
Also see:
Sansui Select System (ad, Jan. 1980)