Accuphase A-50V (1998)

A pure class A stereo power amplifier released in December 1998, with high power output and a precision current feedback design.

Overview

The Accuphase A-50V is a pure class A stereo power amplifier built with M-2000 design technology. It came out in December 1998. It delivers up to 400 watts per channel into 1 ohm in stereo mode. Bridge it for monaural operation and it reportedly puts out up to 800 watts into 2 ohms. It has a current feedback amplifier circuit, balanced input terminals, and a digital power meter for watching output in real time.

Specifications

Rated continuous average power (20 Hz - 20 kHz) Stereo	400W/ch (1 ohm), 200W/ch (2 Ω), 100W/ch (4 Ω), 50W/ch (8 Ω)
Rated continuous average power (20 Hz - 20 kHz) Monaural (bridge connection)	reportedly 800W (2 Ω), 400W (4 Ω), 200W (8 Ω)
Total Harmonic Distortion Factor Stereo	reportedly 0.05% (2 Ω), 0.03% (4 Ω - 16 Ω)
Total Harmonic Distortion Factor Monaural	0.03% (4 Ω - 16 Ω)
IM Distortion Factor	0.003%
Frequency Response	20 Hz to 20 kHz + 0 -0.2 dB at rated continuous average output
Frequency Response	reportedly 0.5 Hz ~ 160 kHz + 0 -3.0 dB at 1W Output
Gain	28.0 dB (both stereo and monaural specifications)
Load Impedance Stereo	1 Ω ~ 16 Ω
Load Impedance Monaural specification	2 Ω ~ 16 Ω
Damping factor	100 (both stereo and monaural specifications)
Input sensitivity (8 Ω load) Stereo	reportedly 0.80 V at rated continuous average power, 0.11 V at 1W output
Input sensitivity (8 Ω load) Monaural	reportedly 1.59 V at rated continuous average power, 0.11 V at 1W output
Input Impedance Balance	40k Ω
Input Impedance Unbalanced	20k Ω
S/N (A correction)	110 dB at input short circuit, rated continuous average output
Digital Output Meter Type	True value display type of power
View Range	0.1W ~ 400.0W (Stereo), 1W ~ 2000W (monaural specification)
Hold Time	1 second / ∞
Switching Type	With Display / Off function
Power Supply	100 VAC, 50Hz/60Hz
Power Consumption No input	reportedly 310W
Power Consumption Electrical Appliance and Material Control Law	550W
Power Consumption 8 Ω rated output	reportedly 380W
External Dimensions	475 mm wide x 239 mm high x 545 mm deep
Weight	45.1kg

Design

The A-50V uses a current feedback amplifier circuit. It feeds the output signal back as current, which keeps output voltage stable under varying loads. The output stage has 10 pairs of power MOS FETs per channel, in parallel push-pull. Each FET is rated at 120W, but each pair handles only 5W. The driver stage also uses power MOS FETs, in a cascode connection that extends frequency response and reduces negative feedback. Signal-carrying parts are high-purity copper with gold plating, including the PCB, earth plate, capacitors, and terminals. The speaker terminals are machined from solid brass, gold-plated, and insulated with mold caps. Power comes from a large toroidal transformer, reportedly 1 kVA, and two 82,000 μF aluminum electrolytic capacitors. The amplifier can be bridge-connected for monaural use and has balanced inputs.