The QL600 is an amplifier made by PIONEER in the 70’s which is commonly known as the QUADRALIZER AMPLIFIER. In that era Quadralizer was a novelty and PIONEER has making with this feature.
Quadralizer is a kind of mixer and divider circuit of 4 audio channel inputs, so the results of this circuit will then go to 4 Power Amplifiers.
SCHEMATIC
The following is a redrawn schematic from the original schematic.
The Power Amplifier circuit uses a single voltage to supply the circuit.
It involves the only NPN transistor as the final amplifier, while the transistor in charge of it is 2SD234.
Q1 act as the pre amplifier of the incoming signal to the power amplifier circuit.
Q2 is a transistor whose job is to amplify the output voltage. Its say with Voltage Amplifier Stages.
Q3 and Q4 are amplifier driver transistors.
Q5 and Q6 serve as final power amplifier transistors.
Because this power circuit uses a single supply voltage, it is mandatory to provide Elco C9 as an AC coupling and DC blocker so that the audio signal can pass to the speaker without being disturbed by the DC voltage.
INFO
With an asymmetric 41 VDC voltage, it is possible for the amp to produce 37 Watts of audio power at a 4 Ohm load.
D1=SV4A is a bias diode which contains 3 diodes in it so that the diode threshold voltage becomes 2.1 to 2.5 VDC.
You can replace it with 3x 1N3595 or 4x 1N4148. ( SUMBER ) .
The 2SD234 transistor is able of producing up to 25 Watts of audio power ( DATASHEETS ).
