Accuphase P-370 (2001)

At 24.4kg, it arrives like a forged ingot of intent—no frivolity, just raw, measured power.

Overview

The Accuphase P-370 is a stereo power amplifier released in March 2001, built with the kind of over-engineering that defines the brand’s high-end reputation. Priced at ¥360,000 at launch, it was never intended for casual listeners. This is a machine for those who demand control, precision, and the ability to drive difficult speaker loads without breaking a sweat. It delivers 150W per channel into 4Ω and 75W into 8Ω, but its real strength lies in its stability—capable of handling down to a 2Ω stereo load (and 1Ω with music signals), a testament to its robust output stage and massive power supply. The P-370 doesn’t just amplify; it governs.

Its design centers around a current feedback amplifier circuit, a hallmark of Accuphase’s approach to minimizing phase error and maintaining wide bandwidth. The output stage uses high-power transistors rated for 150W collector loss and 15A collector current, arranged in triple parallel push-pull configuration and mounted on a large heatsink—necessary given the amplifier’s 475W maximum power draw under test conditions. The power supply relies on a super-ring type toroidal transformer with approximately 700 VA capacity, feeding two 47,000 μF aluminum electrolytic capacitors to ensure instantaneous current delivery. This isn’t just about wattage; it’s about authority.

Balanced operation is supported via dedicated XLR inputs, and the amplifier can be bridged for monaural use, doubling its output into 4Ω or 8Ω loads. The dual speaker terminals allow for bi-wiring, though the manual notes they are normally used by switching between A and B systems. Build quality is industrial: all-metal construction, clean internal layout, and a no-compromise attitude toward signal integrity.

Despite its capabilities, the P-370 doesn’t shout. It operates with a damping factor of 200, ensuring tight control over speaker cones, and achieves a signal-to-noise ratio of 120 dB (A-weighted), making its background virtually silent. Total harmonic distortion is rated at 0.02% across 4Ω to 16Ω loads, rising only slightly to 0.05% at 2Ω. Intermodulation distortion is exceptionally low at 0.003%, suggesting clean reproduction even under complex dynamic demands. Frequency response is ruler-flat from 20Hz to 20kHz at full power, and extends to 160kHz at 1W—far beyond audibility, but indicative of transient speed and phase coherence.

Specifications

Key Features

Current Feedback Amplifier Circuit

The P-370 employs a current feedback topology, a design choice that prioritizes high slew rate and wide bandwidth over traditional voltage feedback. This results in faster transient response and better phase linearity across the audible spectrum. Unlike many amplifiers that roll off sharply at the extremes, the P-370 maintains stability and low distortion even at the edges of its frequency range, contributing to a sense of openness and control.

Triple Parallel Push-Pull Output Stage

Each channel uses three high-power transistors in parallel per side of the push-pull configuration, with each transistor rated for 150W collector loss and 15A collector current. This parallel arrangement reduces individual device stress, improves thermal stability, and allows the amplifier to sustain high current delivery into low-impedance loads. Mounted on a large heatsink, the output stage is built to endure long-term high-power operation without thermal runaway.

Super-Ring Type Toroidal Transformer (700 VA)

At the heart of the power supply is a super-ring type toroidal transformer with approximately 700 VA capacity. This design minimizes magnetic leakage and mechanical vibration while providing a rigid voltage foundation. Paired with two 47,000 μF aluminum electrolytic capacitors, the power supply delivers massive current reserves, ensuring the amplifier never starves under dynamic demand—critical for driving complex speaker loads with authority.

Balanced Input and Bridge-Monaural Operation

The inclusion of balanced XLR inputs allows for noise-resistant connection in high-end systems, especially over longer cable runs. Additionally, the P-370 can be configured for monaural operation via bridge connection, effectively doubling its voltage swing and output power. In this mode, it delivers 600W into 4Ω or 300W into 8Ω, making it suitable as a dedicated subwoofer or main amplifier in bi-amped setups.

Analog Power Meter with Off Switch

A large analog power meter provides real-time visual feedback of output levels, using logarithmic compression to cover a wide dynamic range from -50dB to +3dB. A front-panel switch allows users to turn off both the meter’s movement and backlight—useful in dark listening environments. While purely functional, the meter adds a tactile, industrial aesthetic that underscores the amplifier’s serious intent.

Dual Speaker Terminals for Bi-Wiring

The rear panel includes two sets of speaker terminals (A and B), which can be used to switch between speaker pairs or, when both are engaged, to enable bi-wiring. This allows separate cables for the woofer and midrange/tweeter sections of bi-wireable speakers, though the benefit is debated. Regardless, the terminals are robust and accept thick gauge cables, reflecting the amplifier’s high-current design.

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Service Manuals, Schematics & Catalogs

• Catalog (1991) — archive.org
• Catalog (1992) — archive.org
• Catalog (1990) — archive.org

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