Accuphase AD-250 (1994)
A dedicated phono equalizer unit for playing analog records through the C-250 preamplifier.
Overview
The Accuphase AD-250 is a phono equalizer unit made by Accuphase Laboratory, Inc. and released in June 1994. It was designed specifically to give the C-250 preamplifier analog record playback. It installs directly from the rear panel side of the unit. It cost ￥30,000 at launch. The AD-250 does precise RIAA equalization and supports both MM and MC phono cartridges, each with its own tailored input circuit.
Specifications
| Frequency Response (AD Input) | 20Hz～20kHz ±0.2dB |
| Total Harmonic Distortion | 0.005% |
| Input Sensitivity / Impedance | MM: 8.0mV / 47kΩ; MC: 0.25mV / 10Ω, 30Ω, 100Ω (selectable) |
| Gain | MM→Balanced/Unbalanced: 48dB; MC→Balanced/Unbalanced: 78dB |
| S/N Ratio (IEC-A, shorted input) | MM: 95dB; MC: 79dB |
| EIA S/N | MM: 88dB; MC: 85dB |
| Input Equivalent Noise | MM: -137dBV; MC: -151dBV |
| Maximum Input Voltage (1kHz, 0.005% THD) | MM: 250mV; MC: 8mV |
| Subsonic Filter | 25Hz, -12dB/oct |
Design
The AD-250 uses a gold-plated glass substrate printed circuit board for signal integrity. The MM input is an FET configuration, optimized for high signal-to-noise ratio and high output impedance matching. The MC input uses a differential circuit with low-noise components and reduced NFB loop impedance, so low-level signals come through accurately. MC input impedance and subsonic filter settings are set with internal DIP switches before installation.
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Service Manuals, Schematics & Catalogs
- Catalog (1991) — archive.org
- Catalog (1992) — archive.org
- Catalog (1990) — archive.org