INTRODUCTION
The TDA7480/81/82 are single ended , split supply, class_D amplifiers. The output of the amplifier is a high frequency square wave (around 100Khz), rail to rail, with variable duty cycle.
The audio information is the average value of the output square wave.
To obtain the audio signal, the output must be low pass filtered.
The main issue of this amplifier is the very low dissipated power (the very high efficiency) compared to a normal class AB amplifier.

The preamplifier provides the voltage gain of the overall amplifier. The second stage is the power stage, with a gain 1.5, that is the high efficiency class_D amplifier.
The class_D amplifier stage is done with a multivibrator : with no signal it generates a 50% duty cycle square wave, with signal applied, it changes the duty cycle.
The switching frequency is set by the voltage on pin 9 (DIP20) or pin 6 (MW15).
The output power stage is done with N-ch DMOS power with the upper one supplied by a bootstrap capacitor (C11 in the application circuit).