Here it is shown how to build a powerful audio amplifier using LM741 op amp and darlington pair transistor. In the previous article a simple Audio Amplifier design with uA741 op-amp was illustrated and in the tutorial 3W Audio Amplifier with lm741 op amp a more powerful design was illustrated. Here high power audio amplifier design is illustrated where darlington pair transistor is used along with operational amplifier. The reason for using darlington pair transistor is to increase current at the output and therefore obtain higher power. Darlington pair transistor are used in low frequency application because it takes time to drive the second transistor by the first transistor in darlington circuit. Here darlington pair transistor are used because the audio frequencies are quite low.
LM741 Audio Amplifier Circuit Diagram
The circuit diagram of the audio amplifier with LM741 and darlington pair transistor is shown below.
The input audio signal is fed into the inverting terminal of the op-amp. The 741 op-amp is powered by 12V dual power supply. There are two darlington pair transistors used in the circuit. The first is Q1(BC108) and Q4(BC846) and the second one is Q2(BC178) and Q3(BC857). These two darlington pair transistor are driven by positive and negative power supply. The output of the LM741 op amp is connected to the resistor R6 which is grounded. Because the resistor R6 is grounded, the positive and negative signal current also passes through the resistors R4 and R5. This will develop voltage across R4 and R5 which serves as input to each of the darlington pair transistors.
Tips and Modification
Here to build the LM741 audio amplifier we used dual power supply. Often it is not easy to obtain dual power supply. But there exist solutions to this problem. For example, one can also obtain dual power supply from single power supply which was illustrated in the tutorial LM741 non-inverting amplifier with dual supply from single supply. Another solution to avoid dual power supply is to bias LM741 with split resistor biasing method to operate the operational amplifier with single power supply. An example is provided in the tutorial How to operate LM741 with single supply.
