Audio Database

The

Accuphase P-400
400,000 yen(June, 1979 release)

Description

Stereo power amplifier carrying two sets of monophonic power amplifier.
A Class-A operation changeover switch is carried and it has come to be able to perform selection of Normal operation and Class-A operation.

It is considered so that it may operate also as pure Class-A amplifier by the change by a switch.
The Class-A operation method is an original operation method which the domain of a push pull element of operation always overlaps completely.
A change of operation does not change bias resistance of a circuit with a switch, but the pure electronic formula switch (PAT, PEND) is performing it.

In the output stage, it has triple push pull composition which adopted MOS FET.
Since notching distortion is not generated at the time of transmission of high frequency while MOS FET has the characteristic which is easy to treat compared with a bipolar transistor or SIT, the high region characteristic is improved.

In order to press down coloring on sound quality to the minimum, the mass condenser and input condenser of the NFB loop are removed.
In this state, since it amplifies to a direct current and becomes a cause of failure, while adopting direct-current servo system and cutting passage of a direct current, the drift of the direct-current voltage which appears in an output is also suppressed and stabilized.

All the magnification stages consist of symmetrical type push pull systems of Accuphase original.
It could excel in the linearity, the low distortion could be realized by a little NFB, the high magnification circuit of stability could be constituted, as a result, transitional distorted generating was prevented, and sound quality is improved.

A power-source part considers it as the right-and-left full independence by two transformers, and is taken as the form that two sets of power amplifier was incorporated.
Efficiency has adopted as a transformer IC core transformer which was well excellent in rate of change, and 33000micro per channel of things of a low impedance design of fx2 are adopted as a condenser.

Logarithm compression type peak level meter is carried. It has come to be able to carry out the Direct reading also of the output in 8-ohm load with dB scale.
Moreover, a peak hold is possible by a meter function changeover switch. Since the peak which hold time is about 3 seconds and is produced in the meantime is held, it is convenient for the peak surveillance of program sauce.
At the time of Class-A operation, it changes automatically with an Operation switch so that Output power 50W may be set to 0dB.

In order to enable it to control the gain of amplifier according to total efficiency also including a speaker, the Attenuator for input level adjustments is prepared.
Variable is possible at a 1dB step to -20dB at right-and-left independence.

The input terminal carries not only the usual RCA but 3P canon connector.
The input of the canon connector serves as a 50kohm imbalanced type.

In order to correspond to generation of heat at the time of Class-A operation, the fan for heat dissipation is carried.
In order to make it reach constant temperature after switch-on as soon as possible and to make it stabilize thermally irrespective of the size of an output, he controls a motorised circuit with TEMP.SENSOR and is trying for a fan's number of rotations to change continuously to a temperature change.

The prevention circuit from overheating is carried the sake [ in case circulation of air does not meet the deadline in a bad environment only with air-cooling by a fan ].
A sensor detects it as a heat sink amounting to 100 degrees C, and it is designed at the time of Class-A operation return bias current to the state of Normal automatically, and press down generation of heat.
At the time of operation of Normal, it worked so that the service voltage to output FET might be controlled, and overheating is prevented similarly.

making bridge connection of P-400, and operating one set as one channel by using B-6 which is an optional adapter only for a bridge network, -- Normal -- about -- it is possible to obtain the output of 200W with 700W and a Class-A.

There was a cabinet of natural rosewood finishing as an option.

Rear
Internal The
Main
Bridge

Rating of a mode
Form Stereo power amplifier
Continuation average output (both channel operation)
(20Hz - 20kHz, 0.01% or less of distortion)
Normal Operation
4ohm:300 W/ch
8ohm:200 W/ch
16ohm:100 W/ch
Class-A Operation
4ohm:80 W/ch
8ohm:50 W/ch
16ohm:25 W/ch
THD (both channel operation)
(Output 0.25W - an Output power, 20Hz - 20kHz)
4ohms : 0.01% or less
8ohms : 0.01% or less
16ohms : 0.01% or less
IM distortion (new IHF) 0.003% or less
Frequency response At the time of an Output power: 20Hz - 20000hz+0 -0.2dB (level-control maximum)
Output 1 W:00: 0.4Hz-250000Hz+0 -3.0 dB (level-control maximum)
Output 1 W:00: 0.4Hz-120000Hz+0 -3.0 dB (level-control 6dB)
Dumping factor (new IHF) 150(50Hz)
Input sensitivity/input impedance Output power: 1.6V/50kohm
New IHF and 1W output:0.12V/50kohm
S/N (A-compensation, Normal Operation) 120dB (a rated input, input short-circuit)
100dB (at the time of new IHF and 1W output)
Power output meter Logarithm compression type-40dB-+6dB and an output Direct-reading scale
With a peak hold change
The semiconductor used 34Tr, 20FET, 6IC, 54Di, two optocouplers, two thermistors
Power source 100V, 117V, 220V, 240V / 50 or 60Hz
Power consumption
Normal Operation: 110W (at the time of no inputting)
690W (at the time of an 8-ohm load Output power)
Class-A Operation: 300W (at the time of no inputting)
315W (at the time of an 8-ohm load Output power)
Dimensions the width 445x height 160(piece -- it includeds) x depth of 455mm
Weight 31.2kg
Option Wood cabinet A-10 (15,000yen)
Bridge network B-6 (25,000yen)