Accuphase AD-275

At just 0.8kg, this module is a precision phono stage built for one of the 1990s' most refined preamplifiers.

Overview

The Accuphase AD-275 is not a standalone component. It was designed only for the Accuphase C-275 and C-275V stereo preamplifiers, and it turns a line-stage-only design into one that can play records. It had an original price of ¥100,000 and shows up in a July 1995 sale. It was an optional insert (Einschub) that mounted on the rear panel, so it was a factory upgrade and not a third-party add-on. Its job is to give both moving magnet (MM) and moving coil (MC) cartridges a transparent, low-noise path, in line with the standards of Accuphase's discrete circuit philosophy.

Owners report it was never meant to be flexible across systems. It is a single-system solution. Plug it into the C-275 and the preamp gains full RIAA equalization, balanced and unbalanced outputs, and cartridge-level gain structure calibrated to match the parent unit's architecture. Left and right channels get their own circuit boards, each powered by its own constant-voltage supply and sealed in a rigid aluminum housing to block interference. Gold-plated glass-epoxy substrates carry entirely discrete circuitry. There are no ICs in it.

It is small and light, but the engineering is serious. It uses a current feedback amplifier topology with minimal global negative feedback and slight phase compensation. Accuphase used this approach to preserve transient response and spatial coherence. The MM input relies on FET elements to hold a high input impedance across the audible band, which reduces loading effects on cartridges. The MC side is more tailored: gain is selectable between 60dB and 66dB, and input impedance switches between 10Ω, 30Ω, and 100Ω, which matters for low-output coils. These are hardware-level adjustments built into the circuit.

Specifications

Manufacturer	Accuphase Laboratory, Inc.
Type	Phono equalizer unit exclusively for the C-275 preamplifier
Frequency characteristic (AD Input)	20 Hz to 20 kHz ± 0.2 dB
Total harmonic distortion factor	0.005%
Input Sensitivity / Impedance	AD MM: 4.0mV, 47k Ω; AD MC(60dB): 0.25mV, 10 Ω / 30 Ω / 100 Ω; AD MC(66dB): 0.125mV, 10 Ω / 30 Ω / 100 Ω
Rated output voltage	2.0V
Maximum Input Voltage (0.005% Distortion Factor)	MM:250mV, MC(60dB):8.0mV, MC(66dB):4.0mV
Gain	AD MM Input → Balanced/Unbalanced Output : 48 dB; AD MM Input → Rec Output : 30 dB; AD MC (60/66dB) Input → Balanced/Unbalanced Output : 78/84dB; AD MC (60/66dB) Input → Rec Output : 60/66dB
S/N / input conversion noise (Input short IEC-A correction)	AD MM: 92dB S/N at rated input, -134dBV input reduced noise, 85dB EIA S/N; AD MC(60dB): 79dB S/N at rated input, -151dBV input reduced noise, 85dB EIA S/N; AD MC(66dB): 75dB S/N at rated input, -153dBV input reduced noise, 84dB EIA S/N
Weight	0.8kg

Key Features

Discrete Current Feedback Amplifier Circuit

The AD-275 uses a current feedback amplifier design built entirely from discrete components, with no operational amplifiers or integrated circuits. Accuphase favored this approach for its speed and linearity, and it avoids the phase shifts and slew-rate limitations sometimes seen in voltage-feedback designs. The circuit runs with a small amount of NFB and slight phase compensation, aiming for stability without giving up transient fidelity. According to available documentation, this topology contributes to the unit's low distortion rating of 0.005%.

Independent Channel Boards with Dedicated Power Supplies

The left and right channels sit on separate circuit boards, each fed by its own constant-voltage power supply. This minimizes crosstalk and keeps the channels from interacting through the power supply. The gold-plated glass-epoxy substrates are known for durability and stable dielectric properties, and the design prioritizes long-term performance and resistance to microphonics. Each board is enclosed in a sturdy aluminum housing, which shields sensitive low-level signals from external electromagnetic and mechanical interference.

Adjustable MC Input for Optimal Cartridge Matching

The MC input has two gain settings, 60dB and 66dB, which cover medium-output through ultra-low-output cartridges. Input impedance is switchable across three values: 10Ω, 30Ω, and 100Ω. That lets you match a cartridge's internal impedance, which affects frequency response and damping. Input sensitivities are 0.25mV (60dB) and 0.125mV (66dB), so the stage can pull detail from demanding coils without external step-up transformers.

FET-Based MM Input with Stable High Impedance

The MM input uses FET (field-effect transistor) elements to hold a consistent 47kΩ input impedance across the entire frequency band. Many phono stages see impedance drop at higher frequencies, which can dull transients and alter tonal balance. With FETs, the AD-275 avoids that, and MM cartridges see a stable load from 20Hz to 20kHz. Sensitivity is 4.0mV and maximum input voltage is 250mV, so it handles all standard MM cartridges without overloading, even with hot records or poor VTA alignment.

Plug-In Module for C-275/C-275V Preamplifiers

The AD-275 is not a universal phono stage. It is an Einschub, a plug-in module, designed to install on the rear panel of the Accuphase C-275 or C-275V control preamplifier. It draws power and signal routing directly from the host unit, so there are no external cables, and it is compatible with the C-275's internal architecture. Because of this, it cannot be used with other preamplifiers or integrated systems. That limits its appeal today, but it was always meant as a factory-approved upgrade path.

Collectibility & Value

Market data for the AD-275 is sparse, but recent listings suggest niche demand. A used unit was listed for €890 on August 7, 2025. Original brochures, such as the "Accuphase C-275 AD-275 Prospekt in englisch," have sold for €8 as recently as June 2025. No common failure modes or maintenance issues are documented. Because it relies on discrete components and internal power coupling, any repair should be handled by technicians familiar with Accuphase's design language. Since it depends on the C-275, the AD-275's value is tied to the survival and popularity of its host preamplifier.