Most project PDFs begin with a necessary refresher on amplifier classes. A good resource will not just list them but explain the practical trade-offs:
: Using transistors in the active region to increase signal strength.
At its most fundamental level, an audio amplifier is a two-port circuit that utilizes DC power from a source (like a battery) to increase the amplitude of an incoming AC signal. This process does not "create" energy; rather, it uses the input signal as a template to modulate the larger energy flow from the power supply, resulting in an output that mimics the original waveform with significantly greater strength. How to make an LM386 audio amplifier circuit
PA system, home theater subwoofer, guitar amp. Power: ±35V to ±45V DC (dual rail). Output: 100W into 4Ω.
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