Audio Database

The

Accuphase A-50V
950,000 yen(December, 1998 release)

Description

Power amplifier designed as pure Class-A stereo power amplifier based on the design technique of M-2000.
The reduction in the impedance of an amplifier output and the constant-voltage drive of the speaker are aimed at.

Operation to heat has adopted the power MOS FET of the negative characteristic, and the output magnification stage has gained the linear power which is a thing of ten pears to do for a parallel push pull drive per channel, and was stabilized in this power MOS FET even as for super-low impedance load. Moreover, although the permissible loss electric power of one MOS FET is 120W, the power burden per one pair is set to 5W, and can be using efficiently the small electric power domain which was excellent in the linearity of MOS FET.
Power MOS FET is adopted also as a drive stage, and by making cascode connection of this, the frequency response was broadband-ized and it has contributed to the improvement in sound quality by making a negative return light simultaneously.
By this circuit composition, even if load changes, the Output voltage has acquired the almost fixed value and has become the design in which clipping power had 1ohm of load:513W or 2-ohm:343W or 4-ohm:202W or 8-ohm:110W, and a margin with the actual measurement.

The current feedback type magnification circuit which returns an output signal in the form of current is adopted.
The principle of this circuit lowers the impedance of the input terminal by the side of a return first, detects current, carries out I-V (current-voltage) conversion of that current with a transformer impedance amplifier, and is making the output signal.
In this circuit, since the impedance of a return input portion is very low, it is hard to generate phase rotation, and there is almost no necessity for phase compensation. For this reason, many characteristics are sharply improvable by a little NFB(s).

In A-50V, the changeover switch for bridge connection is carried and it can upgrade to the monophonic power amplifier by bridge connection.

The balance contact button is carried.
Since it goes into two poles at this phase, if the noise ingredient generated in a cable in balance transmission is compounded, only a noise ingredient is canceled and good signal transmission is possible for it.

Copper with high purity is adopted as the parts which a signal passes.
In A-50V, plate-ization with gold is performed on this and a printed board Copper-foil side, the grounded plate with which big ripple current flows, the capacitor terminal, the input terminal, the speaker terminal, etc. are formed into a golden plate.

it can respond to a speaker terminal also at a very-thick speaker cable -- the large-sized speaker terminal is overly equipped.
For a material, it is begun to delete brass Naked material, it is formed into a golden plate for it, and the mould cap is put on it for insulation.

The large-sized Troy Dahl type transformer of the large power capacity of about 1 kVA is adopted as a power-source part, and also it adheres to the unresonated aluminum case of efficient heat dissipation structure using the high load material of the vibrationproofing effect excellent in heat conduction, and the influence on the exterior is suppressed.
The super ring type is adopted as the toroidal transformer adopted as A-50V, the section of the iron core was close to the circle, the coil could also be rolled closely circularly, and since adhesion nature is good, there are few losses and they have made a surge and vibration small.
Furthermore, iron loss and in rushes current are small by enlarging the rate of a bulk density of copper wire small about the cross-sectional area of the iron core.
Moreover, two 82,000-micro F things are carried in the aluminum electrolytic capacitor.

The power meter of a digital display convenient to monitor is carried.
Current and voltage are detected first, with the analog multiplier, the value of electric power is computed and the digital display of this is carried out.
It can perform the change of 1 second and infinite (infinity) time, and the rest time (hold time) of a display can also put out the light, when a display is unnecessary.


Rear
A
Speaker
Power-source
Power MOS FET High-quality
Golden Assy

Rating of a mode
Form Class A stereo power amplifier
Rated continuation average output
(For 20Hz - 20kHz)
At the time of stereo specification (both ch(es) operation) : 400 W/ch (1ohm)
200 W/ch (2ohms)
100 W/ch (4ohms)
50 W/ch (8ohms)
At the time of monophonic specification (bridge connection) : 800W (2ohms)
400W (4ohms)
200W (8ohms)
THD
At the time of stereo specification : 0.05% (2ohms)
0.03% (4ohm-16ohm)
At the time of monophonic specification : 0.03% (4ohm-16ohm)
IM distortion 0.003%
Frequency response 20Hz-20kHz+0 -0.2 dB (at the time of a rated continuation average output)
0.5Hz-160kHz+0 -3.0dB (at the time of 1W output)
Gain (profit) 28.0dB (at the time of a stereo / monophonic specification)
Load impedance At the time of stereo specification: 1ohm - 16ohms
At the time of monophonic specification: 2ohms - 16ohms
Dumping factor 100 (at the time of a stereo / monophonic specification)
Input sensitivity (8-ohm load)
At the time of stereo specification : 0.80V (at the time of a rated continuation average output)
0.11V (at the time of 1W output)
At the time of monophonic specification : 1.59V (at the time of a rated continuation average output)
0.11V (at the time of 1W output)
Input impedance Balance: 40kohm
Unbalance: 20kohm
S/N (A compensation) 110dB (at the time of input short-circuit and a rated continuation average output)
Digital type power output meter Form: The true value display type of electric power
Display range 0.1W-400.0W (at the time of stereo specification)
1W-2000W (at the time of monophonic specification)
Hold time: 1 second /infinity Change type
With a display putting-out-lights function
Power source AC100V, 50Hz/60Hz
Power consumption At the time of no inputting: 310W
Electrical Appliance and Material Control Law: 550W
At the time of an 8ohm Output power: 380W
Dimensions Width 475x height 239x depth of 545mm
Weight 45.1kg