Accuphase M-100 (1981)
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 500 watts continuous average power into 8 ohms from 20 Hz to 20 kHz with 0.01% 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 a low-pass filter with a cutoff at 30 Hz or less, -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 reportedly sold at launch included the Sidewood A-14 mounting set, Heat Dissipation Fan O-81, and Timing Cable TC-11; 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.
eBay Listings
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.
Service Manuals, Schematics & Catalogs
- Catalog — archive.org
- Catalog (1991) — archive.org
- Catalog (1992) — archive.org
Related Models
- Accuphase A-100
- Accuphase A-20
- Accuphase A-20V
- Accuphase A-45
- Accuphase A-65
- Denon POA-800 (1978)
- Eico 3150 (1967)
- Fisher CUSTOM-ELECTRA-I (K-14/K-15) (1957)
- Fisher CUSTOM-ELECTRA IV (E33/E44) (1960)
- Akai AM-2600 (1977)