The Audio amplifier described here uses two small amplifiers like LM380 mounted in bridge. Two small amplifiers LM380 (2.5 W max in each 18 V), which mounted bridge mode make it possible to get a few watts into 8 ohms load.
LM380 mounted on the first non-inverting amplifier, the audio signal connected to + input. The second inverting amplifier mounted on the same audio signal line and connected at the input -. Input (inverting input of U1 and U2 non-inverting input) is not connected to anything. In fact, the internal resistance of 150 Kohm C1 reduces this input to ground. Both amplifiers each have a gain of 34 dB (voltage gain of about 50), the value specified by the manufacturer LM380. With 12 V power supply voltage and input power around 100mV can be generated around 4 W. Power of 5 W is achieved with a supply voltage of 18 V (even with this voltage can reach 6 W without any problems).