This simple audio amplifier can be built at home with few components. You can use it at home or in a car with the 12V car battery as power source. The author’s prototype is shown in Fig. 1 while the circuit diagram is shown in Fig. 2.
The circuit comprises step-down transformer X1, bridge rectifier BR1, 12V voltage regulator IC LM7812, amplifier IC LA4440, 20W loudspeaker LS1, and few other components. Capacitors C1 and C7 connected across the supply terminals are used to minimise ripples/noise signals.
This audio amplifier with dual power source operates at 12V DC, which can be derived in two ways. The first uses a 230V AC primary to 15V, 1A step-down transformer X1. Its 15V AC secondary is connected to bridge rectifier BR1 for rectification of the voltage, which is filtered by capacitor C1. The rectified and filtered voltage is given to the regulator IC LM7812 to get regulated voltage of 12V for the circuit. Any ripples or noise in the voltage are filtered by capacitor C7.
The second, easier, way is to use a 12V, 7Ah battery. Switch S1 is used to select the supply either from the mains or from the battery, especially when the supply from mains is not available.
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