In an SSB/CW receiver, what is the purpose of the audio frequency (AF) amplifier?

In an SSB or CW receiver, the detector (often a product detector) extracts the original audio information from the incoming radio signal. However, this recovered modulation signal is extremely weak, typically just a few millivolts. The audio frequency (AF) amplifier's job is to take this weak audio signal and increase its voltage and power to a level sufficient to drive a speaker or a pair of headphones. Without this amplification stage, the recovered audio would be far too quiet to hear. A common misconception is that the amplifier itself converts the electrical signal into sound. That is actually the job of the speaker or headphones (the transducer). The AF amplifier solely increases the electrical level of the recovered modulation.