p>This book discusses topics related to audio amplifiers and audio systems. In the first part, we discuss the tone control circuit for audio amplifiers, which consists of the architecture of the amplifier circuit, sound volume control, and tone control. The second part discusses audio mixer circuits, with a focus on the architecture of audio amplifier mixer circuits. The third part discusses the audio power amplifier circuit, which consists of the basics of the final amplifier, the power amplifier circuit, and measuring the quality of the sound amplifier.