Listening to music on a self-made system is great. Good-quality audio amplifier circuits can be constructed with minimum components. Described here is an LME49710 based audio amplifier. Author’s prototype is shown in Fig. 1.
Circuit and working
As shown in Fig. 2, circuit diagram of the LME49710 based power amplifier consists of power supply unit and audio amplifier unit.
The power supply unit is a linear type built around transformer X1, bridge rectifier DB107 (BR1), 12V voltage regulator LM7812 (IC1) and a few other components. The 230V AC primary of X1 is stepped down to 15V, 1A. DB107 converts AC to pulsating DC, filtered with capacitors C1 and C2, and the rectified output is given to 12V regulator (IC1). Diode 1N4007 (D1) is used to protect IC1 from reverse voltage. LED1 is used as the power indicator. Resistor R1 is used to limit the current passing through LED1.
The audio amplifier circuit is built around LME49710 (IC2), which is a high-performance, high-fidelity, audio-operational amplifier. The 12V power supply is connected to op-amp power pins. The single-supply operation requires a virtual ground at a voltage level of Vcc/2 = 12V/2 = 6V at the non-inverting terminal of op-amp IC2.
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The circuit can be constructed with a simple voltage divider formed by resistors R4 and R5 and bypassed by capacitor C8. Capacitors C4 and C5 decouple the noise at IC level, where C5 works as an electrolytic decoupling capacitor to reduce low- and mid-frequency noise and C4 reduces high-frequency noise in the power supply lines.