Audio Database

The

Accuphase A-50
880,000 yen(May, 1993 release)

Description

Full-scale pure Class-A stereo power amplifier which the Accuphase supplied the element of the audio technology accumulated since foundation, and the highest grade, and completed in pursuit of the ideal of playback music.

The power MOS FET which has established reputation in sound quality and reliability is adopted as an output stage, and they are N channel power MOS FET and P channel power MOS FET, respectively 10 - It has push pull composition which carried out parallel connection.
There are 120W and, moreover, the permissible loss electric power of one MOS FET is 10. - Since parallel connection, since the burden of the power per one pair is set to 5W, it can be using the small electric power domain excellent in the linearity of MOS FET reasonable. Moreover, the large current by pure Class-A operation also becomes 1/10, and is raising the stability of the whole circuit.
The huge heat sink by aluminum die-casting is adopted as exothermic processing by Class-A operation, and stability is raised to it.
Furthermore, by using Power MOS FET also for a drive stage, switching speed became high, and simultaneously, the system of the negative return became light and has realized improvement in sound quality.
In addition, in order to save from clipping the momentary pulse which sometimes appears by a music signal, the maximum clipping level is set as 100W (8ohms).

An input stage is balanced differential pure complimentary push pull composition, and high input impedance and the FET buffer of the low Output load impedance are adopted as + (non invert), and - an input circuit (invar), respectively.
The vital parts of this input circuit are modularized by the large-sized hybrid IC (60mm x 35mm), a symmetrical circuit is arranged on the base of alumina porcelain, temperature characteristics, the pair noise characteristic, etc. are improved, and the engine performance, reliability, and stability are raised.
Furthermore, this IC was covered by thick aluminum material, and has prevented the influence from the outside.

It is possible to use it as monophonic power amplifier by bridge connection.
the voltage as two amplifier with the same bridge connection -- it is a system which inputs the signal of an inversion phase mutually and connects a speaker to the output end of both amplifier, and if 8-ohm load is connected, it is possible to obtain a twice at the time of a 4-ohm stereo drive as many output as this.
Bridge connection of A-50 uses the polarity of the difference input of two amplifier, and it is making a connection change so that a negative phase signal may be inputted mutually, and it constitutes the pure electronic switch which does not insert a phase inversion circuit.

The full-scale balance input is prepared besides the usual RCA pin jack input, and connection with the apparatus which has a balance output with a XLR type connector is possible.
It is a balance input of A-50 with the non invert (+) of a difference input circuit, and the composition of pouring in a signal as it is to an invert (-) input. For this reason, twin Attenuator of a 1dB step with few interlocking errors is adopted as an Attenuator.
Especially this Attenuator has a small distortion and serves as a high-quality sound type which adopted the resistance object of specular surface finishing excellent in antiwear quality.

Copper with high purity is adopted as the portion which a signal passes, plate-ization with gold is performed from on this, skin resistance is lessened, and the flow of current is made smooth.
Moreover, golden plate-ization has been performed also to the oxygen-free-copper board currently used for the portion treating large current, and improvement in sound quality is further aimed at by using the wire rod of high purity in the shield coat of the circumference of an Attenuator.

The efficient Troy Dahl type transformer of the large power capacity of 1000VA is adopted as a power-source part. This transformer was further enclosed with the aluminum die-casting case, and the influence on the exterior is prevented by fixing to a core using resin with the elastic coefficient which suppresses vibration.
Moreover, the mass capacitor of 56,000 micro Fx2 (electric charge capacity 3.5 clone x2) is adopted as a smooth capacitor. Although the common capacitor is insulated with the vinyl sleeve, in A-50, it is performing soft coating with resiliency called a urethane coating material (Juan TASS - coat), and has a structure strong against vibration.

The power meter of a digital display is carried.
The meter circuit shows the electric power value based on the mounting impedance of a speaker, detects current and voltage, applies this to an analog multiplier, electric power is sent to calculation, and it is sending this value to a micro computer from an A/D converter, and is carrying out the digital display.
The change of 1 second and infinite (infinity) time is possible for the rest time (hold time) of a display. Moreover, when a display is unnecessary, it is also possible to put out the light.

it corresponded also to the very-thick speaker cable -- the large-sized speaker terminal is overly adopted.
This terminal is what began to delete from brass Naked material, formed the golden plate, and put the mould cap of the insulated purpose on it, and can also insert a banana type plug.


Rear
Internal The
Balanced High-quality Power MOS FET
An
Golden Power Filter Large-sized

Rating of a mode
Form Stereo power amplifier
Continuation average output (20Hz - 20kHz)
At the time of stereo specification : 200 W/ch (2ohms)
100 W/ch (4ohms)
50 W/ch (8ohms)
At the time of monophonic specification :
(Bridge connection)
400W (4ohms)
200W (8ohms)
THD
At the time of stereo specification : 0.05% (2ohms)
0.02% (4ohm-16ohm)
At the time of monophonic specification : 0.02% (4ohm-16ohm)
IM distortion 0.003%
Frequency response 20Hz-20kHz+0 -0.2 dB (at the time of a continuation average output level control max)
0.5Hz-160kHz+0 -3.0 dB (at the time of 1W output level control max)
0.5Hz-110kHz+0 -3.0 dB (at the time of 1W output level-control 6dB)
Gain 28.0dB (at the time of a stereo / monophonic specification)
Load impedance At the time of stereo specification: 2ohms - 16ohms
At the time of monophonic specification (bridge connection): 4ohms - 16ohms
Dumping factor At the time of stereo specification: 160
At the time of monophonic specification (bridge connection): 140
Input sensitivity (at the time of 8-ohm load)
At the time of stereo specification : 0.80V (at the time of a continuation average output)
0.11V (at the time of 1W output)
At the time of monophonic specification :
(Bridge connection)
1.59V (at the time of a continuation average output)
0.11V (at the time of 1W output)
Input impedance Imbalanced Input: 20kohm
Balance input: 40kohm
S/N (A compensation) 110dB (at the time of input short-circuit and a continuation average output)
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, a change type
With a display putting-out-lights function
Power source AC100V/117V/220V/240V, 50Hz/60Hz
Power consumption 310W (at the time of no inputting)
550W (Electrical Appliance and Material Control Law)
375W (at the time of an 8-ohm load Output power)
The maximum Dimensions Width 475x height 239x depth of 550mm
Weight 48.5kg