R-A100 is a stereo Receiver also has internal Power Audio Amplifier inside made by KENWOOD at 90s. Its using symmetrical supply 33VDC and deliver 40 Watts at 6 Ohm load.
SCHEMATIC DIAGRAM
This is a re-drawing schematic diagram of R-A100 amplfier:
In this Kenwood amplifier number R-A100, if we look at it, it uses several circuit blocks, including:
- pre-amplifier that uses a differential amplifier system,
- then a voltage amplifier which uses a current mirror,
- then there is a servo driver and
- the last is a Darlington power transistor which functions as a driver and final power amplifier.
Pre-amplifiers use transistors with the number 2SA992 which requires a symmetrical power supply of 15 volts.
GAIN factor of this circuit is determined by the feedback resistor R8 (47 K) comparing to the input resistor that leads to ground.
namely the resistor number R4 with a value of 360 ohms.
It can be said that it occurs more than 50x.
The signal from Q1 will then be amplified by Q4 which then will go to the final amplifier circuit
Then the signal from Q2 will go to transistor Q3 to continue to Q5
Some say Q3 functions as a current mirror
The meeting point of these two transistors, namely Q4 and Q5, is connected by a servo driver transistor Q6 which uses transistor number 2 SC 4137.
The servo driver transistor is controlled by a trimpot with a maximum value of 470 ohms in series with a fix value resistor in hope that this setting will limit the idle current on the final transistor Q7 or Q8.
The final transistors Q7 and Q8 are Darlington transistors, so this circuit looks simple and looks concise.
Thus, it does not require 2 driver transistors.
By using a symmetrical 33 Volts, you will be able to get an output of 100 watts at a load of 4 ohms.
