Name the device used to amplify audio signals in an intercom system.

An audio amplifier is specifically designed to increase the amplitude of audio signals, making it the device of choice for enhancing sound quality and volume in an intercom system. In the context of an intercom system, the audio amplifier receives low-level audio signals generated by a microphone and boosts these signals so they can be transmitted effectively through wires to speakers or other output devices.

This amplification process is crucial for ensuring that the transmitted audio is loud enough to be heard clearly by the receiving end. Without an audio amplifier, the original signals would remain too weak, leading to poor sound quality and reduced intelligibility.

In contrast, while a transformer is utilized in some audio applications for impedance matching or voltage transformation, it does not amplify audio signals in the manner a dedicated audio amplifier does. A microphone converts sound into electrical signals but does not increase their strength, while a speaker reproduces sound from electrical signals without enhancing the audio level itself. Hence, the audio amplifier is the correct choice for this question.