Lo-D DA-703D (1987) | 4DAC - Vibration Cut Solid Base

Released by Lo-D (Hitachi) in 1987, the Lo-D DA-703D was a solidly built integrated CD player developed during the company’s growing focus on digital audio. Its standout feature was an unusually comprehensive approach to vibration control, combined with sophisticated digital processing and a carefully separated digital/analog circuit design.

Lo-D DA-703D Main Specifications

Release year: 1987

Frequency response: 5–20,000 Hz ±0.5 dB

Dynamic range: 100 dB (EIAJ)

S/N ratio: 110 dB (EIAJ)

Channel separation: 105 dB (EIAJ)

Harmonic distortion: 0.003% (EIAJ)

Wow and flutter: Measurement limit, ±0.001% W. peak

Output voltage: 2.0 V

Power consumption: 16 W

Dimensions: 435 W × 129 H × 337 D mm

Weight: 10.5 kg

Digital filter: 4× oversampling

D/A conversion: High-dynamic 4DA converter

Optical output: Provided

Track programming: Up to 24 tracks

Remote control: 20-key keypad

Player controls: 10-key keypad

VC (Vibration Cut) Technology

The DA-703D’s defining feature was its extensive "VC (VIBRATION CUT) mechanism," designed to control unwanted vibration throughout the player. The chassis was firmly supported by a high-rigidity VC solid base made from a special high-density resin. This was further supported by a large three-piece insulator with a 64 mm diameter. Between the main body and VC solid base, 60 cylindrical absorbers were randomly positioned on the contact surface. Their positions were determined using computer simulation analysis, with the aim of effectively preventing vibration from affecting the player. The heavy VC solid base also lowered the overall center of gravity. It helped shift the center of gravity away from the pickup area and toward the center of the chassis. The enclosure itself used a VC enclosure sandwich structure, while the disc table and front panel were separated and floated through a VC loading mechanism. The pickup assembly was mounted on a VC pickup unit made from VC metal. This construction used two steel plates with a thin viscoelastic polymer material sandwiched between them. Three-Spot Pickup System. The pickup system used three laser spots rather than relying solely on the main laser beam. The main beam read the CD signal, while two additional beams positioned to the left and right helped detect tracking errors. The tracking actuator used a pure-metal damping suspension system, designed to provide effective vibration damping during operation. The player also incorporated a direct pit servo system. This system detected tracking errors through reflected laser light while also checking for subtle disc warping and micron-sized dirt. The aim was to prevent unnecessary actuator movement and maintain accurate tracking. 4× Oversampling Digital Filter. Digital processing was another major feature of the DA-703D. Its 4× oversampling digital filter converted the original sampling frequency to 176.4 kHz, allowing high-speed processing and more effective removal of high-frequency noise. The system also suppressed glitch noise produced during digital signal switching. According to the original design description, this eliminated the need for sample-and-hold circuits and low-pass filters, contributing to improved phase and frequency-response characteristics. High-Dynamic 4DA Converter. The D/A converter used four converters rather than two. Where early CD players commonly used one D/A converter for each stereo channel, the DA-703D used two converters per channel, for a total of four. Left and right channels could therefore undergo D/A conversion independently and simultaneously, minimizing timing and phase differences between the channels. The design achieved a stated 24-bit conversion accuracy range. Digital and Analog Circuit Separation. Lo-D also paid considerable attention to electrical isolation. The power supply completely separated the digital and analog sections, with each section receiving its own independent power transformer. This produced a two-transformer configuration intended to reduce interference between the two sections. Five photoisolators were used for optical transmission between digital and analog circuits, providing further electrical isolation. An optical output was also provided for connection to an external D/A converter. The analog section was separated internally as well. The D/A converter and following analog circuitry were separated to suppress interference, while the left and right analog channels were arranged symmetrically. Dedicated components, including high-quality capacitors, high-speed diodes and extra-thick power cords, were also selected for the design. Programming and Playback Features. The DA-703D was more than a basic CD transport and converter. The player featured a 10-key keypad, while its remote control provided 20 keys. Direct track selection was available, together with random programming of up to 24 tracks. A delete-program function allowed unwanted tracks to be excluded from playback. The DA-703D offered six repeat functions covering: All tracks, Random memory, Section, Single track, Random play, Delete, Total Edit Function. The total edit function was designed with cassette recording in mind. It allowed tracks to be arranged for both sides of a cassette tape according to the desired recording length. The unusual Twin Line Music Table display made this easier to manage. The display showed 20 tracks in two columns, with programmed and scheduled tracks on the upper line and completed tracks on the lower line. This made functions such as total editing and random playback easier to follow. The Lo-D DA-703D was a serious CD player with an unusually logical engineering approach. Its combination of extensive vibration control, three-spot tracking, 4× oversampling, four-D/A conversion and digital/analog isolation shows how much attention Lo-D devoted to extracting reliable performance from the emerging CD format. Original sale price in Japan ¥89,800

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