Sony CDP-705ESD
A 29.7-pound compact disc player that Leonard Feldman measured at 0.002% THD and called the best-tracking machine he'd ever put a scratched disc into.
Overview
The CDP-705ESD is a big piece of kit. It weighs 29.7 lbs. (13.5 kg), sits in a 16 15/16-inch-wide chassis, and cost $1,500 when it arrived. That weight and price put it squarely in Sony's ES tier. The spec sheet: frequency response from 2 Hz to 20 kHz within ±0.3 dB, signal-to-noise ratio of 106 dB (EIAJ), dynamic range of 97 dB, THD of 0.0025% at 1 kHz, channel separation of 100 dB at 1 kHz, and wow and flutter below 0.001%. Those are manufacturer's numbers. The interesting part is how they held up under independent measurement.
The player is built around four-times oversampling with true 16-bit dual D/A conversion. Earlier Sony designs used two-times oversampling. The point wasn't extra musical information. It was pushing the unwanted noise sidebands up to around 176.4 kHz, which let Sony use a gentler final analog filter. The digital filter circuits, working with new high-speed converters, held band-pass ripple below 0.001 dB and delivered more than 80 dB of stop-band rejection above 25.7 kHz. Separate digital and analog power supplies with subregulators, plus optical coupling between the digital filter stage and the demultiplexer and delay stages, kept the analog section isolated from the digital noise. Switching diodes serve as supply rectifiers, and RC filters sit on the secondary side of the power transformer to keep external noise and hum out.
The tracking system is where this player earns its reputation. Sony's advanced Error Prediction Logic monitors the laser pickup's position 8,000 times per second. When an error first appears, the circuit memorizes its parameters. On the next revolution it compares the incoming signal against that stored data by microprocessor. Before the third rotation it has already calculated the probable location and duration of the error and told the servo to respond with the exact current needed to hold tracking. The circuit divides each disc rotation into more than 1,065 discrete intervals, a check roughly every 0.34°. The Envelope Differential Servo Detection system carries over from earlier ES models. It catches data dropouts before they turn into tracking errors and freezes the pickup in place when no digital data is present, which speeds recovery from gross disc defects.
Connectivity is generous for the period. There are fixed and variable analog outputs, a headphone output rated at 28 mW into 32 ohms, and a digital output at 0.5 V peak to peak. The variable output runs from 0 to 2.0 V. A slide switch above the digital jack must be set to "On" for the digital signal to appear, and with it engaged, analog output is unavailable at either line output or the headphone jack. The variable level can be adjusted from the supplied remote, and the tiny knob on the front panel actually rotates because the gain is changed by a motorized precision potentiometer. Up to 20 selections can be programmed in any order. Direct track and index access are available from the front panel or remote, and the player offers repeat modes including repeat of a defined section, plus the shuffle play Sony had introduced some time earlier.
Audio (July 1987, p.52) handed the CDP-705ESD to Leonard Feldman for an equipment profile, and his bench results are the reason collectors still seek it out. Maximum deviation from flat response across the audio band came in at +0.2 dB and −0.6 dB, the worst case occurring only at 20 kHz. Harmonic distortion at 0-dB recorded level was, in his words, by far the lowest he had measured for any CD player — under 0.002% at most frequencies, and possibly lower still, since his measuring gear bottomed out around that figure. Unweighted S/N measured 95.0 dB and A-weighted 99.7 dB. Separation hit a full 100 dB at low and mid frequencies, easing only to 95 dB at 10 kHz and 92.0 dB at 16 kHz, and it was identical in both directions. Dynamic range measured an impressive 107 dB, and wow and flutter was too low to measure with his test equipment. Output linearity stayed within 0.1 dB down to 80 dB below maximum recorded level and was off by less than 1.0 dB at −90 dB. CCIF twin-tone intermodulation distortion came in at 0.001% at 0-dB level, rising only to 0.0015% at −10 dB.
Two results stand out even among those numbers. Audio (July 1987, p.58) reported that the CDP-705ESD was the first player Feldman had tested whose de-emphasis was perfect, not deviating by so much as 0.1 dB. The same review (p.60) noted plenty of CDs that simply sounded better on this unit than on many others. The spectrum analysis of a 20-kHz test signal showed the expected out-of-band beat at 24.1 kHz, a consequence of the gentle analog filtering, but no other spurious outputs above or below the test frequency. Most oversampling players of the day couldn't match that. On the tracking bench, the player sailed through Feldman's special "defects" disc and rescued several discs he'd been ready to discard because they caused sustained mistracking and muting on other machines. He'd seen Sony demonstrate the Envelope Differential Servo Detection system before, but experiencing it on his own test bench was, he wrote, nothing short of remarkable.
Some practical notes for collectors. These were $1,500 players when new, and the used market reflected that depreciation quickly. By 1988 a mail-order listing had a CDP705ESD at $950, and by 1995 the estate sale of Bert Whyte's equipment listed one at $500. The machine is heavy and built like it. The motorized potentiometer and dual power supplies are serviceable but not trivial to work on. Nothing in the available documentation covers common failure modes or parts availability, so buyers should assume the usual caveats for a player of this age apply. What the documentation does establish is that its measured performance, particularly the perfect de-emphasis and the tracking system, put it at the top of what redbook CD playback could do in 1987.
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