Figure 1.  Circuit Diagram for a Simple LM380-Based Audio Power Amplifier

The circuit shown in Figure 1 is a very simple audio power amplifier.

The main component of this circuit is the LM380 audio amplifier. The simplicity of this circuit is made possible by the LM380's minimal requirements for external components, since it is already internally equipped with the necessary biasing, compensation, and gain circuits for audio amplification.

The circuit in Figure 1 uses the LM380 in non-inverting mode, with the inverting input left open (the inverting input may also be tied to ground, either directly or through a resistor or capacitor). C2 is used to decouple Vcc from ground.  The optional RC circuit at the output (pin 8) is used for added stability, i.e., to eliminate oscillations in an RF-sensitive application.

Figure 2 shows how the circuit in Figure 1 can have a variable gain simply by connecting a potentiometer across the inputs of the LM380. Rv is varied to adjust the gain of the amplifier.

Figure 2.  Circuit Diagram for a Variable-Gain LM380-Based Audio Power Amplifier

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