Yamaha

M-4

Amplifier, Power

Main Details
Maker Yamaha Brand
Function
Channels/Tracks
  • 2 × Channel
Form Factor Standard Width
Signal Path Analog Hardware
Made In Japan
Date Produced 1978-1982
Dimensions
(H × W × D)
Weight 18.5 kg
Power Source Mains
Frequency Response 10 Hz - 100 Khz (8 Ohm, 50 W, 0.02% THD)
Notes A smaller and less powerful followup design to the M-2 introduced earlier. The Japanese version is called the B-2 and is sufficiently different from the M-4 to not be included here. This is a class AB transistor design conservatively rated at 170 Watts per channel into 4 ohms and capable of driving most loudspeakers, including inefficient designs and those with difficult impedance curves. It has Yamaha's typical refined sound for the period. Some M-4 amplifiers include a voltage selector switch. The original sale price was 250,000¥ in 1979.

Other features:
- Gold-plated RCA inputs
- Gold-plated speaker outputs
- 2.5 mm pure copper bus
- Phase-corrected polystyrene caps
- Ground termination
-AC-DC input coupling selector

Excerpt from the owner's manual:
"The voltage amplifying stage employs a cascode-connected differential two-stage circuit throughout.
The use of a Dual FET input and a new cascode bootstrap circuit in the first stage and a cascode-connection, current-mirror and push-pull output in the pre-driver stage ensures a high degree of stability, low distortion and improved high-frequency characteristics.

In the driver and the power amplifier, a three-stage emitter follower is paralleled with pure complementary OCL SEPP circuitry using high-fT transistors. This accounts for wide bandwidth, high output and low distortion.

Two extremely large 15,000µF capacitors, two separate constant-voltage power supplies for the voltage amplifying stage, and the use of a pure copper plate earth line for ultra-low impedance guarantee greatly reduced intermodulation distortion, improved separation and absolutely stable operation.

Except for the chemical capacitors in the power supply section, mylar and styrol capacitors are employed throughout ; layout of parts, wiring, earth line as well as many other aspects have been given due consideration."
Additional Specifications
Rated Power 8 Ohm 100 W/ch 20 Hz - 30 Khz, 0.005% THD @ 8 Ohms
Rated Power 4 Ohm 170 W/ch 20 Hz - 30 Khz, 0.005% THD @ 4 Ohms
Intermodulation Distortion <0.002% @ half rated power
Bandwidth DC - 100 KHz (-0.7 / +0.5 dB)
Damping Factor 8 Ohm 200
Damping Factor 4 Ohm 100
Stereo Separation 118 dB (IHF-A) 90 dB @ 1 Khz 70 dB @ 20 Khz
Max Power Consumption 900 W
Displays/Indicators
Power LED Watts / 8 Ohm
Overload LED Watts / 8 Ohm
Connections
Analog Stereo RCA (Phono, Cinch)
Ground Binding Post
Speaker A Spring Terminal
Speaker B Spring Terminal
Controls
Parameter: Power
Control Type: Latching Push Switch
Range: On/Off
Parameter: Speaker A
Control Type: Latching Push Switch
Range: On/Off
Parameter: Speaker B
Control Type: Latching Push Switch
Range: On/Off
Parameter: L-ch Trim
Control Type: Rotary Pot
Range: 0-10
Parameter: R-ch Trim
Control Type: Rotary Pot
Range: 0-10
Parameter: Input Coupling Mode
Control Type: Slide Switch
Range: AC-DC

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