The SM3000 is an amplifier made by PIONEER in the 70’s that produces up to 130 Watts of audio power at 4 Ohm loads but 90 watts continuous power at 8 Ohm loads.
INFO
The appearance of the amp is as follows:
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From the appearance of this amplifier it looks only as a power amplifier but there is no tone control.
Meanwhile, if we look at the contents in this amplifier, it looks special, because it is sturdy and factory class.
SCHEMATIC
The service manual of the amplifier contains pages on PCB layout and schematic diagrams of amplifier.
Then I took the power amplifier section for collection and review. Here’s what the power amp schematic looks like after crop and editing.
From the schematic, its appears that the power amplifier circuit consists of 4 blocks, they are:
- Initial amplifier with differential amplifier uses 2 transistors Q1 and Q2 ( A726).
- Voltage Amplifier Stage, using 2 levels of transistors Q3 and Q4 (2SC627).
- Driver Amplifier, with Darlington technique on each part of the signal ( Q5 C484 series with Q7 C783, Q6 series with Q8 ).
- the lastly: Final Power Amplifier, using 2 pairs of transistor numbers 2SC1079 and 2SA679.
NOTE
The amplifier use 51 VDC simmetrically supply to reach up to 150 Watt of audio output.
The Final Power transistor ( C1079 & A679 ) able to make audio output until 100 Watt of each.
The power amplifier has features zero output biasing by turning the trimpot VR1.