The Driver Amplifier amplifies the weak electrical signal from microphone and make it suitable for power amplification. Thus, an amplifier which is used before power amplifier is called driver amplifier. As all amplifier driver amplifier is also a cascade amplifier.
Circuit Description of 10-Watt Audio Amplifier
The projects shown in figure 1 is of 10-Watt Audio Amplifier, which is basically a combination of various amplifier i.e. pre-amplifier, driver amplifier, and a push-pull amplifier. Here in the project “10-Watt Audio Amplifier” transistor T1 act as pre-amplifier, T2 as driver amplifier and transistors T3 with T4 as push-pull amplifier.
The output of microphone is given to the base of transistor T1 (Pre-amplifier) through coupling capacitor C1. The output of transistor T1 is available at collector which is used to drive driver amplifier. The driver amplifier amplifies the weak signal and make it suitable for power amplification. The output of driver amplifier is given to the base of push-pull amplifier (T3 and T4). The output of push-pull amplifier (transistors T3 and T4) taken from emitter through 1 resistor (resistors R7 and R8). The output is given to speaker through coupling capacitor C5. Resistor R9 is a feedback resistor which is connected to base of transistor T4.
Similarly, another feedback network is designed using resistor R5 and capacitor C4 which is connected to the emitter of preamplifier transistor T1. When supply voltage of 22V is given to the circuit the power obtained at the output is of 10W, which changes according to the supply voltage. As the supply voltage is low the power obtained at output also become less.
NOTE: Heat sink is required due to heating problem at power amplifier at stage. So proper heat sing must be connected to the transistor T3 and T4.
PARTS LIST OF 10-WATT AUDIO POWER AMPLIFIER
|Resistors (all ¼-watt, ± 5% Carbon)|
|R1 = 390 KΩ
R2 = 120 KΩ
R3, R4 = 39 KΩ
R5 = 3.3 KΩ
R6 = 15 Ω
R7, R8 = 1 Ω
R9 = 560 KΩ
|C1 = 220 pF (Ceramic Disc)
C2 = 220 µF/16V (Electrolytic Capacitors)
C3 = 22 µF/10V (Electrolytic Capacitors)
C4 =2.2 nF (Ceramic Disc)
C5 = 1000 µF/16V (Electrolytic Capacitors)
|T1 = BEL548 (NPN Transistor)
T2 = BE188 (PNP Transistor)
T3 = AC187 (NPN Transistor)
T4 = AC188 (PNP Transistor)
|LS1 = Speaker|