Exclusive M4a

Commentary

This is a stereo power amplifier that achieves high-quality sound in a class-A amplifier circuit.

The input stage of the differential amplifier drives the push-pull pre-driver stage and drives the final stage of 8 power transistors (4 parallel connection) per channel.
A class A push-pull circuit is excellent because it has no notching or crossover distortion. Therefore, there is little distortion when NFB is not applied. Moreover, it has excellent stability and transient characteristics especially in the low frequency range because the power supply does not vary depending on the power.

We have developed and used special specifications for each sound quality part, such as condensers such as Mylar, STICON and electrolytic capacitor, and non-inductive wound non-magnetic resistor.

In order to minimize distortion, oxygen-free copper wire is used as wiring material.

The substrate is a 140 μ m thick copper foil glass epoxy substrate.
While conventional glass epoxy boards were used by attaching 35 μ m copper foil, we have adopted 140 μ m copper foil, which is four times larger than conventional ones, in order to reduce DCR (direct current resistance) and inductance in the board.

In order to ensure stable performance and reliability, all input / output terminals and assembly terminals are gold-plated to greatly improve the conduction characteristics.
In the past, nickel plating was applied to the base layer in order to stabilize the plating. However, since nickel is ferromagnetic, distortion caused by hysteresis occurred.
The newly developed pin jack used in the M4a has been plated on a non-magnetic substrate with stability equal to or better than that of nickel, preventing distortion and obtaining stable contact performance.

The power cord is double-insulated, high reliability and large capacity (15A) power cord.
In addition, the core wire of the power cord is colored white and black, and the connection with the AC plug is managed to unify the polarity.

The connection code uses a oxygen-free copper wire as the material and a gold-plated plug made of non-magnetic material as the pin plug to minimize the occurrence of strain in the connection code. The connection code structure is different from the conventional coaxial structure in that it uses a star quad system in which opposing core wires of the signal wire are twisted together to reduce inductance. In addition, the signal wire is completely shielded by a conductive polymer material and braiding.
As a result, it is possible to transmit high-quality signals with low distortion and low loss.

To cope with the heat generated by a class A amplifier, the chassis is configured to form a cooling duct. Two fans installed in the lower part of the cabinet are used for forced-air cooling. In addition, the fan is operated at low voltage and low speed to suppress the rotational noise.

In addition to the conventional output point DC potential detection circuit which combines a relay and an electronic circuit, a thermal detector using a positive star and a protective circuit using a thyristor are added.

Model Rating

Type	Stereo power amplifier
Circuit system	Differential 2-Stage, PP Drive, 2-Stage Darlington, Quadruple PP Pure complimentary service OCL (Class A Operation)
Effective output (20 Hz to 20 kHz, both channels driven)	50W + 50W (8 Ω)
Harmonic distortion factor (20 Hz to 20 kHz)	0.01% or Less (Effective Output) 0.01% or Less (at 25W output) 0.01% or Less (at 1W Output)
Cross modulation distortion factor	0.01% or Less (Effective Output) 0.01% or Less (at 25W output) 0.01% or Less (at 1W Output)
Output Bandwidth (IHF, both channel drives)	5 Hz to 100 kHz (Harmonic Distortion Factor 0.05%)
Frequency response (at 1W output)	3 Hz ~ 60 kHz + 0 -1dB
Input Sensitivity / Impedance	Input1, 2 : 1 V, 2V/50k Ω
Output terminal	Speaker : 8 Ω
Damping factor (20 Hz to 20 kHz, 8 Ω)	30 or more
Subsonic filter	8 Hz, 6dB/oct.
S/N (IHF, A-network, short circuit)	110 dB or more
Semiconductor used	Transistor : 59 IC : 6 Diode, etc. : 67 pcs
Power supply voltage	100 VAC, 50Hz/60Hz
Rated power consumption (maximum power consumption)	320W (Electrical Appliance and Material Control Law)
Power outlet	Power switch not linked : 1 system
External dimensions	Width 468x Height 206x Depth 385 mm
Weight	27.3kg
Attachment	Relay cord with pin plug