Commentary　

This is an authentic pure A class stereo power amplifier that Accuphase has developed since its establishment and put in the highest grade elements and audio technology, pursuing the ideal of reproduction music.

The output stage employs a power MOS FET with a reputation for sound quality and reliability. N-channel power MOS Push-pull configuration in which FET and P-channel power MOS FETs are each connected in 10-parallel.
The allowable loss power of one MOS FET is 120W, and the power load per pair is 5W due to the 10-parallel connection. It is easy to use the low power region with excellent linearity of FET, and the high current by pure class A operation is reduced to 1/10, improving the stability of the whole circuit.
A large heat sink made of aluminum die-cast is used for heat treatment in class A operation to improve stability.
Furthermore, by using a power MOS FET in the drive stage, the switching speed is increased, and at the same time, the negative feedback system is lighter and the sound quality is improved.
The maximum clipping level is set to 100W (8 Ω) to save the momentary pulses that sometimes appear in the music signal from clipping.

The input stage has a balanced differential pure complimentary service push-pull configuration, and FET buffers with high input impedance and low output impedance are used for the + (non-inverted) and - (inverted) input circuits, respectively.
An important part of this input circuit is modularized by large 60mmx35mm hybrid ICs. A symmetric circuit is placed on the base of the alumina ceramics to improve the temperature and noise characteristics.
In addition, the IC is covered with thick aluminum to protect it from external influences.

It can be used as a monaural power amplifier with bridge connection.
Bridge connection is a method in which two amplifiers are supplied with signals of the same voltage and opposite phases and a speaker is connected to the output terminals of both amplifiers. When an 8 Ω load is connected, it is possible to obtain twice the output of 4 Ω stereo drive.
The bridge connection of A-50 utilizes the polarity of the differential inputs of two amplifiers. By changing the connection so that the opposite phase signals are input to each other, a pure switching circuit without inserting a phase inversion circuit is constructed.

In addition to the normal RCA pin jack input, there is a full-scale balanced input. The XLR-type connector allows connection to devices with balanced outputs.
For the balance input of A-50, the signal is directly injected into the non-inverting (+) and inverting (-) inputs of the differential input circuit. For this reason, a 2-channel attenuator with 1-dB steps is used as the attenuator.
This attenuator is a high-quality type with a mirror finished resistor that has a particularly low distortion factor and excellent wear resistance.

High-purity copper is used for the part where the signal passes. The metal plate is made of gold to reduce the skin resistance and smooth the current flow.
In addition, gold plates are applied to the oxygen-free copper plates used for the parts that handle large currents, and high-purity wire materials are used for the shield coat around the attenuator to improve sound quality.

The power supply section uses a high-efficiency toroidal transformer with a high power capacity of 1000 VA. The transformer is enclosed in an aluminum die-cast case and fixed inside with a resin with an elastic coefficient that suppresses vibration, thereby preventing external effects.
The smoothing capacitor is a large capacitor of 56,000 μ Fx2 (charge capacity 3.5 clone x2). Ordinary capacitors are insulated with a vinyl sleeve, but the A-50 is made with a flexible soft coating called urethane coating (Fantas-Coat) to resist vibration.

Equipped with power meter with digital display.
The meter circuit displays a power value based on the mounted impedance of the speaker, detects current and voltage, uses an analog multiplier to calculate the power, and sends this value from the A/D converter to the microcomputer for digital display.
The display stationary time (hold time) can be switched between 1 second and infinite (∞) time. It can also be turned off when the display is not required.

Uses ultra-large speaker terminals that can be used with very thick speaker cables.
This terminal is machined from solid brass into a gold plate, covered with a mold cap for insulation, and a banana-type plug can be inserted.

Model Rating

Type	Stereo Power Amp
Continuous average power (20 Hz to 20 kHz)	Stereo : 200W/ch (2 Ω) 100W/ch (4 Ω) 50W/ch (8 Ω) Monaural : (bridge connection) 400W (4 ω) 200W (8 Ω)
Total Harmonic Distortion Factor	Stereo : 0.05% (2 Ω) 0.02% (4 Ω ~ 16 Ω) Monaural : 0.02% (4 ω - 16 ω)
IM Distortion Factor	0.003%
Frequency Response	20 Hz to 20 kHz + 0 -0.2 dB (continuous average output, level control max) 0.5 Hz ~ 160 kHz + 0 -3.0 dB (at 1W Output, Level Control Max) 0.5 Hz ~ 110 kHz + 0 -3.0 dB (at 1W output, level control -6dB)
Gain	28.0 dB (both stereo and monaural specifications)
Load Impedance	Stereo specification : 2 Ω ~ 16 Ω Monaural specification (bridge connection) : 4 Ω ~ 16 Ω
Damping factor	Stereo : 160 Monaural (bridge connection) : 140
Input sensitivity (at 8 Ω load)	Stereo : 0.80 v (continuous average output) 0.11 v at 1W output Monaural : (bridge connection) 1.59 v (continuous average output) 0.11 v at 1W output
Input Impedance	Unbalanced input : 20k Ω Balance input : 40k Ω
S/N (A correction)	110 dB (input short, continuous average output)
Output Meter	Type : True Power Type View Range : 0.1W ~ 400.0W (Stereo) 1W ~ 2000W (monaural specification) Hold Time : 1 second, ∞, switchable With Display / Off function
Power Supply	100 VAC / 117 V / 220 V / 240 V, 50Hz/60Hz
Power Consumption	310W (no input) 550W (Electrical Appliance and Material Control Law) 375W at 8 Ω load rated output
Maximum External Dimensions	475 mm wide x 239 mm high x 550 mm deep
Weight	48.5kg