Pioneer M-77

Commentary

This is a stereo power amplifier that achieves excellent dynamic range with sufficient power.

In order to achieve a high-power amplifier that reproduces excellent musical performance, the circuit configuration is determined through both trial listening and measurement.

The circuit adopts first stage cascade connection differential amplification, last stage triple push-pull and pure complimentary service OCL circuit.
By using a cascaded differential amplifier in the first stage, DC stability is enhanced and high-frequency characteristics are improved.
The pre-driver stage (Class A driver stage) is a push-pull circuit with a current mirror circuit. The current mirror circuit enhances the DC balance, and the push-pull circuit suppresses high gain and even-order harmonic distortion.
The driver stage and output stage are 2-stage Darlington circuits, and three power transistors are connected in parallel in a triple push-pull configuration. By making the output stage triple push-pull, the current flowing through each transistor is reduced to 1/3, and the operating point with good linearity can be selected, so that a large output can be obtained at a low distortion rate.

Because it is composed of carefully selected elements, consideration is given to fine texture at minute output.

The power supply section uses a large toroidal transformer with low internal resistance and good regulation, and the capacitor uses 15,000 μ Fx4.

Equipped with a peak power meter.

Model Rating

Type	Stereo power amplifier
Circuit system	First stage cascade connection differential amplification triple push-pull Pure complimentary service OCL circuit
Effective power (Both channel drive, 20 Hz to 20 kHz)	250W + 250W (4 Ω) 250W + 250W (8 Ω)
Harmonic distortion factor (20 Hz to 20 kHz)	Effective power : 0.1% 0.05% at 125W output (8 Ω) 1W output (8 Ω) : 0.05%
Cross modulation distortion factor (50 Hz : 7 kHz = 4 : 1, 8 Ω)	Effective power : 0.1% 0.05% at 125W output 0.05% at 1W output
Output Bandwidth (IHF, both channel drives)	5 Hz ~ 30 kHz (Distortion Factor 0.1%)
Frequency characteristic	5 Hz to 80 kHz + 0 -1dB
Input terminal	Input : 2V/50k Ω
Output terminal	Speaker : 4 Ω, 8 Ω
Damping factor	50 (20 Hz ~ 20 kHz, 8 Ω)
Signal-to-noise ratio	110 dB (IHF, A-network, short circuit)
Semiconductor used	Transistor : 55 Diode, Other : 81
Power supply voltage	100 V, 50Hz/60Hz
Power consumption (Electrical Appliance and Material Control Law)	450W
Maximum Power Consumption	1200W
External dimensions	Width 480x Height 186.5x Depth 445 mm
Weight	24.3kg
EIA standard rack mounting unit	4U