Accuphase P-400

Commentary

Stereo power amplifier equipped with two monaural power amplifiers.
Equipped with a class A operation selection switch, Normal operation and Class-A operation can be selected.

It is designed to operate as a pure A-class amplifier by switching with a switch.
Class A operation mode is an original operation mode in which the operation area of the push-pull element always completely overlaps.
The operation is switched by a pure electronic switch (PAT, PEND) instead of switching the circuit bias resistance with a switch.

The output stage is a triple push-pull configuration using MOS FET.
MOS FET has easy-to-handle characteristics compared with bipolar transistor or SIT, and at the same time, high-frequency characteristics are improved because notching distortion does not occur in high-frequency transmission.

In order to minimize coloring for sound quality, the large capacitor and input capacitor of the NFB loop have been removed.
In this state, even direct current is amplified and causes failure. Therefore, the DC servo system is adopted to cut off direct current passage and to suppress the drift of direct current voltage which appears in the output to stabilize it.

All amplification stages are composed of symmetric push-pull system of Acuphase original.
It is excellent in linearity, realizes low distortion rate with a small amount of NFB, and constructs an amplifier circuit with high stability. As a result, it prevents transient distortion and improves sound quality.

The power supply section is completely independent on the right and left by two transformers, and two power amplifiers are incorporated.
The transformer employs an IC core transformer with high efficiency and excellent fluctuation rate, and the capacitor employs a low impedance design of 33000 μ fx2 per channel.

Equipped with a logarithmic compression type peak level meter. Along with the dB scale, the output at 8 Ω load can be read directly.
In addition, peak hold is possible by the meter function changeover switch. The hold time is approximately 3 seconds, and the peak generated during that time is held, so it is convenient for peak monitoring of the program source.
In class A operation, it is automatically switched by the Operation switch so that the rated output 50W becomes 0 dB.

An attenuator is provided to adjust the input level so that the gain of the amplifier can be controlled by the total efficiency including the speaker.
The left and right are independent and can be varied up to -20dB in 1 dB steps.

The input terminal is equipped with a 3P cannon connector in addition to the normal RCA connector.
The input of the cannon connector is 50k Ω unbalanced type.

In order to cope with heat generation during class A operation, a heat radiation fan is mounted.
In order to reach a constant temperature as soon as possible after the switch is turned on and to achieve thermal stability regardless of the output, the motor drive circuit is controlled by a temperature sensor so that the rotational speed of the fan changes continuously in response to temperature changes.

An overtemperature circuit is installed in case air cooling by a fan alone is not enough in an environment with poor air flow.
When the heat sink reaches 100 ° C, the sensor detects it, and when it is in Class A operation, the bias current is automatically returned to the Normal state to reduce heat generation.
In normal operation, the voltage supplied to the output FET is controlled to prevent overheating as well.

By using B-6, which is an adapter exclusive for bridge network sold separately, it is possible to obtain an output of approximately 700W in Normal mode and 200W in A-class mode by bridge-connecting P-400 and operating it as one channel.

There was a cabinet with natural rosewood finish sold separately.

Model Rating

Type	Stereo power amplifier
Continuous average output (both channel operation (20 Hz to 20 kHz, Distortion Rate 0.01% or Less)	Normal Operation 4 Ω : 300W/ch 8 Ω : 200W/ch 16 Ω : 100W/ch Class-A Operation 4 Ω : 80W/ch 8 Ω : 50W/ch 16 Ω : 25W/ch
Harmonic distortion factor (both channel operation Output 0.25W ~ Rated Output 20 Hz to 20 kHz)	4 Ω : 0.01% or less 8 Ω : 0.01% or less 16 Ω : 0.01% or less
IM distortion factor (new IHF)	Not more than 0.003%
Frequency characteristic	Rated Output : 20 Hz ~ 20 kHz + 0 -0.2 dB (Level Control Maximum) Output at 1W : 0.4 Hz ~ 250 kHz + 0 -3.0 dB (level control maximum) Output at 1W : 0.4 Hz ~ 120 kHz + 0 -3.0 dB (level control -6dB)
Damping factor (new IHF)	150(50Hz)
Input Sensitivity / Input Impedance	Rated output : 1.6V/50k Ω New IHF, 1W output : 0.12V/50k Ω
S/N (A-compensation, Normal Operation)	120 dB (Rated Input, Input Short) 100 dB (at new IHF, 1W output)
Output meter	Logarithmic compression type -40dB to + 6 dB and output direct reading scale With Peak Hold Switch
Semiconductor used	34 tr, 20 fet, 6 ic, 54 di, 2 opto-coupler, 2 thermistor
Pwer	100 V, 117 V, 220 V, 240V/50, 60 Hz
Power consumption	Normal Operation: 110W (no input) 690W (at 8 Ω load rated output) Class-A Operation: 300W (no input) 315W (at 8 Ω load rated output)
External dimensions	Width 445x Height 160 (Including Legs) x Depth 455 mm
Weight	31.2kg
Sold Separately	Wood Cabinet A-10 (¥ 15,000) Bridge Network B-6 (¥ 25,000)