Incredibly, a 78XX type voltage regulator can be used to amplify low frequency (audio) signals in the configuration shown in the figure. The load must have a resistance that limits the circuit current to 1 ampere and the value of the input capacitor can be changed depending on the signal impedance. The input of this circuit is of low impedance, which requires a good excitation power. For a 7806, for example, where a 10 ohms load limits the current to less than 1 amp, the circuit gain will be 10 times.
