The QM800A is a quadrophonic amplifier made by Pioneer in the 70’s.
At that time Quadrophonic was a new thing in the audio world because it used 4 amplifier systems or Surround, which is a term for audio that seems to “rotate” around the listener’s head or audio listener.
INFO
According to the service manual, this amplifier uses 4 amplifiers that have the same output power.
With the intention that the sound is the same big and loud for the 4 speakers that will be installed in the front 2 pieces and 2 pieces at the back as well.
The Power Amplifier produces up to 35Watt of power at 8 Ohm each channel.
SCHEMATIC DIAGRAM
The service manual contains the PCB layout, block diagram, and schematic for this amp.
I only picked up the power amp schematic for collecting and reviewing purposes.
Click to enlarge
From the schematic above it appears that this amplifier uses a 4-level amplifier system:
- Initial amplifier, using a differential system with Q1, Q3 that using transistor 2SA726
- Voltage amplifier, using transistor Q5 numbered 2SC1124.
- The amplifier drivers, Q7 and Q9 numbered 2SD356 and 2SB526.
- Power Amplifier. Q11 and Q13 numbered C1402 and 2SA744.
In the initial amplifier transistor section there is a circuit to determine 0 Volt at the output of the circuit.
NOTE
Diode Zener D1 dan D2 adalah zener 13VDC dengan daya 500mW.
Power Supplay menggunakan Simetris 31VDC.
Transistors C1402 and A744 have a power capability of up to 70 watts each. ( SOURCE ).
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