The Dual 701 is the quietest turntable ever made. Not only in our judgment, but in that of the first independent test laboratory to evaluate its performance. This has been accomplished by an entirely different kind of motor, designed expressly for the 701, and by a very innovative approach to the problem of resonance.
Instead of the familiar, high-speed AC motor, the 701 has an all-electronic, low-speed Dc motor with feedback-controlled speed precision. Because this motor rotates at the record speed, 33-⅓ or 45 rpm, the need for speed-reduction systems such as friction-idler or rim-belt is eliminated. Instead, the platter is rotated directly by the motor, and the record spindle is the top of the motor shaft.
The 701 motor is so quiet and free from vibration that it does not require any isolation mounting but is mounted directly to the chassis. Dual's exclusive design of overlapping coils, a unique feature of the motor, eliminates the successive pulses common to every other existing motor, including other electronic types, high speed or low speed.
Another Dual innovation serves to prevent interference from reaching and affecting the stylus. Two separate anti-resonance filters, each tuned to a specific resonance range, are located within the counterbalance housing.
One filter is tuned to the resonant range of the tonearm/cartridge system; the other, to the resonant range of the chassis. Each filter serves to cancel out the resonant energy that would otherwise impart spurious signal to the stylus. For those who would like to know more about the 701 motor and the anti-resonance filters.
THE Dual 701 is designed for only single play. But like other Duals, it can be operated either fully automatically, or as a manual turntable.
Because of the unique motor and anti-resonance filters, the 701 is slightly quieter than the 1229. but if you now own a 1229, or any other current Dual, you will detect only a minor difference.
Full-size twelve-inch dynamically balanced, die-cast platter
The 701 platter rests directly on the rotor and rotates with it at the selected speed. Every platter is cost from a single piece of special zinc alloy which is then individually machined and balanced while rotating at high speed. Any imbalances, however minute, are graphically revealed by computerized gauges and precisely corrected. The platter's full twelve-inch diameter, 9,7 pounds of weight (platter plus rotor) and perfect dynamic balance combine to provide optimum flywheel effect.
Electronically-regulated, direct-drive motor with exclusive overlapping coil system.
The EDS-1000 motor developed by Dual for the 701 is an all-electronic, low-speed, brushless, DC motor with Hall-effect feedback control, and energized by a regulated power supply. Unlike conventional DC motors, commutation (electrical switching) is not done by brushes and commutator ring. The 701 motor has electronic switching commutation and speed regulation. Two Hall-effect generators drive four switching transistors which produce a rotating magnetic field in the motor's field coils. Depending on the position of the rotor, the magnetic field causes the four magnetic pairs on the rotor to be pushed and pulled continuously. The field coil design is unique and exclusive with Dual. Two stacked coil layers, each consisting of eight bifilar-wound (coreless) coil, offset by 22,5°, achieving a gapless rotating magnetic field that eliminates the successive pulses of magnetic flux typical of all other motor designs. The absence of magnetic spring-back or other rotation irregularities can be demonstrated by turning the rotor manually, no resistance will be sensed. Also, because of the coreless field coils the motor is free of hysteresis or eddy-current losses and the disturbances of pole frequencies.
The rotational speed of the 701 motor is controlled electronically. A voltage which is a function of motor speed is fed to an electronic regulating circuit, and is compared to a constant standard voltage dreived from a regulated power supply. Any difference in these two voltages causes an immediate change in the motor current, hence the motor speed. The rotor is a barium ferrite ring magnet, magnetized in eight segments (poles) on its lower front surface. A steel plate serves as a megnetic return circuit. The regulated power supply makes the speed independent of variations in power-line voltage or frequency. Speed can be set directly to either 33-⅓ or 45 rpm. Thus, the platter is driven directly by the rotor, without need for any speed-reducing linkoge such as friction-idler or rim-belt.
Further, in contrast to the high speed (1800 rpm) vibrations of the conventional AC motor, the 701 motor is so free from vibration that it is mounted directly to the chassis without introducing any rumble. In summary, the 701 electronic direct-drive system, with its over-lapping gapless design, rotating magnetic return circuit and coreless field windings, is the most advanced drive system available for record playback today.
Specifications
Drive; Electronically-controlled direct-drive system Dual EDS-1000
Platter: Non-magnetic, dynamically-balanced, detachable
Platter Weight: 2,9 kg
Platter Diameter: 305 mm
Total Rotating Mass of Drive System (Rotor with Platter): 4,4 kg, moment of inertia 460 kp/cm²
Run-up Time: 2 - 2,5 sec on 33-1/2 rpm
Platter Speeds: 33-⅓ and 45 rpm - Electronically switchable, automatic tonearm lowering coupled to speed change
Pitch Control: Separate for both speed adjustable in each case with variable resistor, with setting scales, range of adjustment 8%
Speed Check: with light stroboscope for platter speed of 33-⅓ and 45 rpm, adjustable for 50 or 60 Hz
Sensitivity Of Light Stroboscope (for 0,1% Speed Deviation): 6 graduations per minute (at 50 Hz); 7m2 graduations per minute (at 60 Hz)
Overall Speed variations: less than ±0,03% (DIN 45 507)
Signal-to-Noise Ratio (DIN 45 500)
Rumble Unweighted : more than 50 dB
Rumble Weighted : more than 70 dB
Tonearm: Torsion resistent, extra long tubular aluminum tonearm in super flat unversal 4-point gimbal suspension, tonearm balance weight with double acting vibration damping (2 anti-resonators)
Effective Tonearm Length: 222 mm
Offset Angle: 25° 20'
Tangential Track Error Angle: 0,16°/cm
Tonearm Bearing Friction (related to stylus point)
Vertical : < 0,007 p
Horizontal : < 0,015 p
Tracking Force: 0 - 3 g continuously variable, with 1/10 p calibration in the range from 0 - 1,5p, reliable as from 0,25 p tracking force.
Pick-up Head: Detachable, suitable for all pick-up cartidges with 1/2" mounting and a deadweight of 2 to 10 g (including mouting material)
Adjustable Overhang: 5 mm
Power Requirements: 110 - 130 V, 220 - 240 V, AC 50/60 Hz
Power Consumption: 2,5 watts (approx), Motor during play <50 mW
Dimensions (W x H x D): 420 x 147 x 365 mm
Weight 10,9 kg
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