Accuphase M-2000 (1997)

Solid-state monoblock power amplifier sold in December 1997, with very high power output and precision engineering.

Overview

The Accuphase M-2000 is a solid-state monoblock power amplifier made by Accuphase Laboratory, Inc. It went on sale in December 1997 at ¥1,000,000 per unit. The goal was constant voltage drive no matter how the loudspeaker impedance swings. To get there it uses a current feedback amplifier circuit, which puts signal current in the feedback loop instead of voltage. Each unit weighs 50kg and measures 475mm wide, 252mm high, and 545mm deep. The chassis is massive aluminum diecast heat sinks plus front and rear panels, all forming a rigid structure.

Specifications

Output Power (8 Ω)	250W
Output Power (4 Ω)	500W
Output Power (2 Ω)	1,000W
Output Power (1 Ω)	2,000W
THD	0.03% (4–16 Ω), 0.05% (2 Ω), 0.1% (1 Ω)
IM Distortion	0.003%
Frequency Response	20Hz–20kHz ±0.2dB (rated output)
Gain	28.0 dB
Damping Factor	400
Input Impedance	Balanced: 40k Ω, Unbalanced: 20k Ω
Power Consumption	950W (max, per Electrical Appliance and Material Control Law)
Weight	50 kg (110 lbs)
Dimensions	475mm W × 252mm H × 545mm D
Power Supply	100 VAC, 50/60Hz

Design

The M-2000 uses a current feedback amplifier circuit with 22 parallel push-pull transistors per monoblock. Each one is rated for 130W collector dissipation and 15A collector current, which adds up to 5,700W combined collector dissipation. The output transistors are mounted directly to the aluminum diecast heat sinks. Construction is modular. The power supply has a 1.5 kVA "Super Ring" toroidal transformer in a damped enclosure, and two 40,000 μF filtering capacitors. All the major signal path parts are gold-plated - PCB traces, ground bars, capacitor bus bars, input jacks, and speaker terminals. The front panel has a large analog power meter with peak hold and logarithmic compression. Balanced inputs use pin 3 as positive, and there is a phase inversion switch. From the unbalanced input, the amplifier is noninverting.

Context

The M-2000 was developed to deliver constant voltage drive into wildly fluctuating loudspeaker impedance. Accuphase Laboratory, Inc. was founded by former Kenwood engineer Jiro Kasuga in late 1972. Kenwood held partial ownership of Kensonic (Accuphase) until the mid-1990s.