Exclusive M4

Commentary

In order to create a truly high-quality product, this is a stereo power amplifier limit of possibilities based on the essence of audio.
It was developed with the aim of the highest quality in design, used parts, circuit structure and performance. It is carefully hand-made from the assembly of the parts to the final adjustment.

Class A amplification is used for the circuit.
The input circuit drives the push-pull predriver stage with a differential amplifier, and leads it to the final stage of four power transistors connected in parallel (eight per one channel).
The push-pull circuit of class A operation does not generate notching distortion or transient crossover distortion due to the base accumulation effect of the transistor, and the distortion when NFB is not applied is essentially small. Therefore, there is no sound even at a small output, and it is possible to convey the nuance of the source faithfully.
In addition, since the power supply voltage does not fluctuate regardless of the power level, the low-frequency stability and low-frequency transient characteristics are excellent. Since a large current flows even when there is no signal, the temperature of the radiator is kept constant and excellent thermal stability is obtained.

Equipped with a peak power meter at the front. This meter uses a logarithmic compression circuit so that it can read directly over a wide range without changing the sensitivity.
In addition, a large external magnetic type meter with a quick rise and good damping is used for the meter. The indicator is moved to an easy-to-see position even when the volume is low, and the indication is given with good follow-up even when a large pulsed signal is input.

All parts are made with highly reliable special specifications.
Glass epoxy boards with high strength and reliability are used for the printed circuit board. In addition, highly accurate and highly reliable parts are carefully selected from transistors to resistors.
The power supply section is equipped with a large cut core transformer and a 33,000 μ Fx2 power supply capacitor with low leakage flux and excellent regulation.

In order to cope with the large amount of heat generated by the class A amplifier, a cooling duct is formed inside the chassis in consideration of heat radiation effect, and forced air cooling is performed using two fans attached to the lower part of the cab net.
In addition, low voltage and low speed operation are used to suppress fan noise.

In addition to the conventional output point DC potential detection circuit combining a relay and an electronic circuit, a heat detector using a positive star and a holding circuit using a thyristor have been added to the protection circuit.
When the temperature of the radiator rises abnormally, the positive star detects heat, and the thyristor activates the current limiting switch built into the power amplifier to lower the temperature of the radiator and simultaneously drive the relay to disconnect the speaker.
At this time, the protection indicator lamp remains lit and this state is maintained unless the power switch is reset.
In addition to conventional fast response and reliable protection circuits, this heat-sensitive protection circuit also addresses safety in the event of a fan outage.

Two input systems are installed, and 1 v or 2 v can be selected according to the output of the preamplifier.

Equipped with 8dB/oct CR-type subsonic filter at 8 Hz, switch ON/OFF is possible as needed.

As it is suitable for a hand-made high-end amplifier, the measured value of each unit is attached as it is.

Model Rating

Type	Class A stereo power amplifier
Circuit system	Differential 1-stage PP drive 2-Step Darlington Quadruple PP Pure complimentary service OCL system (Class A Operation)
Effective power	50W + 50W (8 ω, 20 Hz to 20 kHz, B.C. D)
Harmonic distortion factor	0.1% or Less (Effective Output) 0.03% or less (at 1W output)
Cross modulation distortion factor	0.1% or Less (Effective Output) 0.03% or less (at 1W output)
Output bandwidth	5 Hz ~ 70 kHz (IHF, Double-channel Drive)
Frequency characteristic	3 Hz ~ 60 kHz + 0 -1dB
Input sensitivity	Input1, 2 : 1 v, 2 v
Subsonic filter	8Hz(6dB/oct)
Output terminal	Speaker (8 Ω)
Damping factor	30 or More (8 Ω)
Peak meter indication range	0.005W ~ 100W (-40dB ~ + 3 dB)
Semiconductor used	Transistor : 59 IC : 6 Thyristor : 1 unit Diode and others : 60
Power consumption	320W
External dimensions	Width 468x Height 206x Depth 385 mm
Weight	27.3kg