Audio Database

Image of the M-25
Commentary

This stereo power amplifier was developed based on the design concept of "Magni-wide Power Range," which requires full power reproduction with low distortion over an ultra-wide band as well as within the audible band.

In order to enable low-distortion full-power regeneration in the ultra-high frequency range, we have developed and adopted a group transistor RET (Ring Emitter Transistor) with superior high-frequency switching characteristics. This transistor consists of hundreds of low-power transistors with superior high-frequency characteristics that are synthesized in parallel. This transistor is designed to increase the breakdown strength and power consumption without compromising the high-speed switching characteristics of the low-power transistors.
Structurally, it is an epitaxial planar transistor, named ring emitter transistor because the emitters are arranged in a toroidal ring around the base electrode.
Compared with conventional power transistors, RET has excellent switching characteristics, good signal response, and low carrier accumulation.

A DC amplifier configuration is adopted to ensure sufficient power at the minimum distortion rate even in the ultra-low frequency range. Since the DC amplifier configuration does not have a capacitor in the NFB circuit, it eliminates transient distortion and phase distortion to the ultra-low frequency range.
In addition, to ensure sufficient power, it is equipped with a large power supply section consisting of a large transformer independent on the left and right sides and a large 22,000 μ Fx4 capacitor.

The M-25 performs class A operation up to 3W and class AB operation above 3W. This achieves both high sound quality and high output. In addition, since the power utilization factor is high efficiency close to that of a general class B amplifier, the peak component of the music signal is reproduced with allowance.

To reduce the impedance inside the amplifier, we use a pure copper plate 12 mm wide and 1 mm thick on the ground side from the power capacitor to the speaker terminal. We also use extra-thick Line 14 (2.03 φ spring wire) for the hot line from the rectifier to the speaker terminal, which is 1/4 the resistance value of the conventional thick wire. In addition, by increasing the charging capacity of the power capacitor, we are able to cope with sudden changes in current sufficiently.
In addition, the copper foil on each circuit board has been doubled to 70 μ m, and the collectors of the two power transistors are connected by a short bar made of a pure copper plate 12 mm wide and 1.2 mm thick. This reduces impedance.

High separation is achieved by monoconstruction which reduces the separation between the left and right channels.

Gold plating is applied not only to the input / output terminals but also to the terminals on the board.
In the power relay of the protection circuit, a parent-child relay with two contacts for small current and large current is adopted to prevent deterioration of the contacts.

Model Rating
Type Stereo power amplifier
Circuit system First stage differential current mirror load 3-stage Darlington
Parallel push-pull pure complimentary service OCL circuit
Class-AB Operation, DC Amplifier Configuration
Effective output (both channel drive)
8 ohms : 120W + 120W (5 Hz to 30 kHz, 0.01% harmonic distortion)
120W + 120W (5 Hz to 80 kHz, Harmonic Distortion Factor 0.05%)
4 ohms : 120W + 120W (5 Hz to 20 kHz, 0.02% harmonic distortion)
Harmonic distortion factor (5 Hz to 30 kHz, 8 Ω) Effective power : 0.01%
At 60W output : 0.01%
0.007% at 1W output
Intermodulation distortion factor (50 Hz : 7 kHz = 4 : 1, 8 Ω) Effective power : 0.006%
60W output : 0.005%
0.005% at 1W output
Output Bandwidth (IHF, both channel drives) 5 Hz to 45 kHz (Distortion Factor 0.01%)
5 Hz ~ 100 kHz (Distortion Factor 0.05%)
Frequency characteristic 5 Hz ~ 200 kHz + 0 -1dB at 1W Output
Input terminal Input : 1V/50k Ω
Output terminal Speaker : 4 Ω ~ 16 Ω
Damping factor 100 (20 Hz ~ 20 kHz, 8 Ω)
Signal-to-noise ratio (IHF, A-network, short circuit) 120dB
Channel separation 1kHz:105dB
100kHz:70dB
Semiconductor used Transistor : 55
Diode, other : 53 pcs
Power supply voltage 100 V, 50Hz/60Hz
Power consumption 280W (Electrical Appliance and Material Control Law)
Maximum Power Consumption 800W
External dimensions Width 420x Height 153x Depth 370 mm
Weight 22.5kg