AVR35 is a radio receiver and Multi input amplifier made by HARMAN KARDON of the 2000s. Its able to produce up to 45 Watts of audio output power.
INFO
This amp uses a remote control to select inputs, adjust levels and tone controlling.
Appearance of the unit:
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This unit looks beautiful and powerfull.
SCHEMATIC
If we look at the repair manual, it appears in the book that these amps involve a digital system in their control system.
I just took the power amplifier section for collection and review.
If we look at the schematic, it appears that the amplifier consists of several parts, they are:
- Preamplifier and mute switch.
- Current mirror and voltage amplifier.
- Servo drivers.
- Amplifier Drivers.
- Power Amplifier.
The preamplifier uses a Q404 Q404 transistor with the number KTC3200. Q406 serves as a current stabilizer. Transistor switch ON or OFF depends on the incoming DC signal from D402. When there is no input voltage from D402 then transistor Q406 will turn off and the audio is muted.
The output of this preamp circuit then goes to the base of Q412 and Q414.
Q412 and Q416 are transistors that act as current mirrors which then end up in the collector of Q420 which happens to be parallel to Q422.
Meanwhile the incoming signal to Q414 will be amplified again by Q422.
Because the output of the transistor is taken from the collector point, then Q422 and Q424 become a pair of voltage amplifier transistors.
This audio signal will be level limitation by the Q426 transistor which acts as a servo driver.
The servo driver serves to provide a DC bias to the power transistor so that it does not waste too much current and prevents excessive heat when it amplifies a high audio level.
The amplifier driver uses a complementary Darlington technique or call it the Sziklai system to get a very large current gain, moreover considering the speaker load too low.
Therefore, the transistors are Q430 and Q434 paired with Q432 and Q436.
Lastly, the Power Amplifier uses a pair of transistor numbers C5197 and A1940.
NOTE
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The 2SC5197 able to make audio output until up to 80 Watt ( SOURCE )
