The amplifier section of sansui receiver 771 uses the OCL principle which uses a symmetrical 35VDC supply voltage and produces an output power up to 32 Watts per channel at 8 Ohm speaker loads.
INFO
The 771 is an AM/FM Stereo radio receiver with a built-in hifi amplifier that was produced in the 70’s, between 1970 and 1979 and its was becoming a classy hifi device for its time.
Here is the appearance of this SANSUI’s radio amplifier:
There is an exclusive impression on this radio. And I’m sure that the equipment is expensive in its era. While inside of the radio amplifier is like as follows:
SCHEMATIC
The following is an edited and cropped schematic diagram derived from the original one:
From this schematic, it can be seen that the power amplifier circuit consists of 5 parts, namely:
- Firstly is Preamplifier block, its using a pair of 2SA640 transistors.
- Secondly is Voltage Amplifier Stages or V.A.S, using transistor number 2SC1124.
- Servo driver, using transistor number 2SC281.
- Driver Booster, C1124 and A706-3.
- Lastly is the Final Power Amplifier, using a pair of C1402 transistors.
NOTE
The circuit uses a 0 Volt DC output voltage determination feature, by using VR01 and 2 pieces of diodes in order to maintain zero voltage stability.
VR03 is in charge of maintaining the setting so that the voltage on the emitter resistor of the power transistor its always at 20mVolt.
Transistor power 2SC1402 able to producing the power output up to 70 Watts.
( DATASHEETS HERE )
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