Accuphase A-65

Commentary

This is a class A stereo power amplifier with full balance transmission by adopting the instrumentation amplifier system as a successor to the A-65.

The amplifier section employs an instrumentation amplifier system, and the signal path from the input terminal to the power amplifier stage is fully balanced for transmission.
As a result, it is not only excellent in CMRR (Common Mode Rejection Ratio) and distortion factor, but also robust against environmental changes such as external noise, improving stability and reliability as a power amplifier.

An MCS + circuit is mounted to reduce noise.
MCS (Multiple Circuit Summing-up) is a circuit method to improve various characteristics by connecting the same circuit in parallel. MCS + circuit is an evolution of this circuit, and further noise reduction is realized by expanding the parallel operation part to the A class drive stage of the current-voltage conversion part.

A current feedback amplifier circuit is mounted.
In this method, the output signal is fed back in the form of an electric current. Since the impedance of the feedback input part is extremely low, phase rotation hardly occurs, and various characteristics can be greatly improved with a small amount of NFB.

The output device uses a power MOS-FET, which is well known for its sound quality and reliability, and has 10 parallel push-pull drives per channel.
The MOS-FET has excellent frequency characteristics and high input impedance, reduces the effect of load on the drive stage in the previous stage, and provides stable operation against thermal fluctuation. High sound quality is achieved by driving this element in a pure A-class system.
The pure A-class system is a system in which the power supplied from the power supply is constant regardless of the presence or absence of a music signal. It is less susceptible to external influences and has high stability. However, the output stage itself generates a large amount of heat. To cope with this problem, the A-65 uses large heat sinks installed on the left and right sides of the casing to increase the heat radiation effect, eliminating heat concentration inside and ensuring stable operation.

The power supply section employs a high-efficiency toroidal power transformer housed in an aluminum die-cast case and a 82,000 μ Fx2 large-capacity smoothing capacitor, achieving 480W/ch at an ultra-low impedance load of 1 Ω.

Equipped with 4-stage gain control to reduce residual noise.

A 2-method power meter is used for the meter, and two types of display can be switched between digital 5-digit numerical display and bar graph 25-point LED display.
This meter uses a Hall element to detect output current, and is a digital power meter that displays true power values.
The peak value hold time can be switched between 1 second and ∞, and the meter circuit can be turned ON/OFF.

The front panel has a balanced and unbalanced input selector switch.

It is equipped with a large speaker terminal into which Y lug and banana plug can be inserted.

Equipped with a mode selector switch, bi-amplifier connection is possible by switching to dual mono.
It can also be used as a high-output monaural power amplifier with bridge connections.

Model Rating

Type	Stereo power amplifier
Rated continuous average output (20 Hz to 20 kHz)	Stereo type (both channel operation) 480W + 4860W (1 ohm load, music signal only) 240W + 240W (2 ohm load) 120W + 120W (4 ohm load) 60W + 60W (8 Ω load) Monaural specification (bridge connection) 960W (2 Ω load, music signal only) 480W (4 Ω load) 240W (8 Ω load)
Total harmonic distortion factor	Stereo type (both channel operation) 0.07% (2 Ω Load) 0.05% (4 Ω ~ 16 Ω Load) Monaural specification (bridge connection) 0.03% (4 Ω ~ 16 Ω Load)
IM distortion factor	0.01%
Frequency characteristic	20 Hz ~ 20 kHz + 0 -0.2 dB (at rated continuous average output) 0.5 Hz ~ 160 kHz + 0 -3.0 dB (at 1W Output)
Gain	28.0 dB (Gain switch at max) Both stereo and monaural specifications
Gain switching	Max, -3dB, -6dB, -12dB
Load impedance	Stereo specification : 2 Ω ~ 16 Ω Monaural specification : 4 Ω ~ 16 Ω * Only for music signals, stereo 1 Ω and monaural 2 Ω can be loaded
Damping factor	400
Input Sensitivity (8 Ω load, Gain switch : max)	Stereo specification 0.87 V (at rated continuous average output (60W)) 0.11 V (at 1W output) Monaural specification 1.74 V at rated continuous average output (240W) 0.11 V (at 1W output)
Input impedance	Balance : 40k Ω Unbalanced : 20k Ω
S/N (A correction, input short)	115 dB (Gain Switch Max) 121 dB (gain switch -12dB) Rated continuous average output
Output meter	Digital meter : 5-digit display, range switching (10W/100W/1000W) Bar graph meter : 25-point display Hold Time : 1 Second / ∞ Switching Type * With display / lights-out function, monaural specification : Same value display on left and right
Pwer	100 VAC, 50Hz/60Hz
Power consumption	280W (no input) 530W (Electrical Appliances and Materials Safety Act) 380W (at 8 Ω load rated output)
Maximum external dimensions	Width 465x Height 238x Depth 515 mm
Weight	43.0kg