Accuphase M-100 (1981)

Name: Accuphase M-100
Brand: Accuphase

Monaural power amplifier released in July 1981 with 100 watts output into 8 ohms and a pioneering digital peak power display.

Overview

The Accuphase M-100 is a monaural power amplifier introduced in July 1981, designed to deliver high-current performance with low open-loop output impedance for precise speaker control. It produces 100 watts continuous average power into 8 ohms from 20 Hz to 20 kHz with 0.03% total harmonic distortion and a damping factor of 300 at 50 Hz into 8 ohms. The amplifier supports load impedances from 2 Ω to 16 Ω and features a signal-to-noise ratio of 120 dB (A-weighted).

Specifications

Power Output	100W (8 Ω, 20Hz–20kHz)
THD	0.03%
Damping Factor	300 (50Hz, 8 Ω)
Dimensions	475 mm (W) × 190 mm (H) × 428 mm (D)
Weight	27.5 kg
Release Date	July 1981
Original Price	¥500,000 (1 unit)

Design

The M-100 uses 24 output transistors—12 parallel push-pull bipolar transistors per channel—with a total collector power capacity of 4.8 kW, mounted on dual large heat sinks with a bias balance circuit to prevent thermal runaway. The drive stage employs MOS FETs in an Accuphase-original configuration, while the pre-drive uses cascode-connected push-pull circuitry. The input stage uses a dual FET cascode bootstrap differential push-pull design that eliminates the need for an input capacitor. A DC servo amplifier suppresses DC drift. The amplifier operates in pure class A up to 5W output. It features a 25-contact step-type attenuator with 1 dB precision and ±0.1 dB error, and includes selectable low-pass filters (10/17/30/50 Hz, -12dB/oct). The world’s first power amplifier with a digital peak power direct reader, it displays output from 0.001W to 999W on a 3-digit LED via a 12-bit A/D converter and 4-bit microprocessor, with hold times of 0.5s, 3s, or 30 minutes. A phase switch and sync signal terminal support multi-amp setups, including bridged operation for up to 1.6 kW into 8 Ω.

Market

Accessories sold at launch included the Sidewood A-14 mounting set (¥16,000), Heat Dissipation Fan O-81 (¥8,000), and Timing Cable TC-11 (10m, ¥3,000); a 1.5m timing cable was included. Used units were listed for €9,400 on willhaben.at (March 22, 2026) and €9,600 on Audio-markt (September 23, 2023). One unit appeared in a Yahoo Auctions listing for ¥800 on January 14, 2026.

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