NAD S500
A single-disc CD player that spec'd like a lab instrument and shipped with the schematic in the box.
Overview
Open the service manual for the NAD S500 and the first thing that greets you is a specification sheet that reads less like a consumer deck and more like a bench reference. Contemporary audio-press coverage of the era, such as the classified and retail listings in HiFi-Stereo (August 1985, p.79), reflected the brand's reputation for value-oriented hi-fi, with NAD among the marques discounted heavily through mail-order dealers. The digital-to-analogue conversion is handled by a Crystal multi-bit chip running 20-bit resolution, feeding a 5-pole active analogue filter. The frequency response is quoted at 5 Hz–20 kHz, ±0.15 dB — a tolerance tight enough that most players of the era wouldn't dream of printing it. That number tells you what the designer was chasing: not warmth, not romance, but flatness. A player this linear is a player that gets out of the way.
The rest of the spec block backs up the impression. Total harmonic distortion at 0 dB and 1 kHz is listed at 0.002%, dynamic range at 98 dB, and linearity holds to ±0.5 dB all the way from 0 dB down to −90 dB — meaning quiet passages decay the way they were recorded rather than collapsing into digital grit. Signal-to-noise is A-weighted at 110 dB with de-emphasis engaged, and channel separation measures 100 dB at 1 kHz and 99 dB at 20 kHz, so the stereo image stays put even in the treble. Wow and flutter is listed as "unmeasurable," credited to quartz accuracy — which is the manual's way of saying the clock is doing its job.
Outputs are where the S500 shows its serious side. The rear panel carries an unbalanced line output alongside left and right balanced line outputs, plus both an AES/EBU balanced digital output and a coaxial digital output — and a BNC connector appears in the parts list as well. For a single-disc player to offer balanced analogue and AES/EBU digital outs is a statement: this was built to slot into a studio or a high-end rack, not just a living-room shelf. Output level at 0 dB is 2.2 Vrms into a 120 Ω output impedance. Digital error correction uses CIRC with double error correction in both C1 and C2, the standard Sony/Philips serial data format on the unbalanced side and AES/EBU on the balanced.
The build is modular and serviceable in a way that collectors appreciate. The parts list breaks the player into a PSU board, a control board, a DAC board, and a front panel board, with a separate power switch assembly. The transport is a CD mechanism with loader, and there's a dedicated display module behind a display lens. The chassis is assembled from a fascia, top cover, base plate, and separate left and right side panels, with a clamp bar and CD mechanism bars holding the transport steady. A heatsink pair sits inside, and the transformer rides on its own holder and plate. None of this is glamorous, but it's the kind of construction that makes a twenty-year-old player repairable instead of disposable.
Owners also get the small courtesies: the packing list includes a remote control handset, an audio cable, and a NAD Link cable for system integration, plus the warranty card and manual. The front panel carries a 10 mm power button and four 6 mm input buttons, a display lens, and a CD tray lid. Fusing is region-specific — North American units take time-lag fuses rated 500 mA and 2 A at 250 V, while European units take 250 mA and 2 A SEMKO/VDE-rated fuses — which is the sort of detail that matters enormously the day a fuse blows and you're staring at the wrong rating.
What the S500 represents, then, is NAD's attempt to build a reference-grade single-disc player with the same no-nonsense service philosophy as its amplifiers. The balanced outputs and AES/EBU digital out put it in a different league from the budget decks the brand was famous for, and the ±0.15 dB frequency tolerance and 0.002% THD are the kind of figures that hold up on a test bench rather than just in a brochure. Collectors chasing one should look for the remote and the NAD Link cable, confirm the transport tray cycles cleanly, and check the fuse rating against their region — the manual is explicit about that for good reason.
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