Preamplifier (Control Center) — Allows input selection and volume control, may also provide tone controls. Traditionally these also include a phono preamp circuit, but as not everyone needs that feature these days, some omit it.

Phono Preamp. — As mentioned above, this is the circuit necessary to equalize and boost the signal from a phone cartridge up to so-called line level. These can be purchased separately if your system doesn’t include this feature and you want to add a turntable.

DAC (Digital to Analog Converter). Changes a stream of sound encoded as digital data into an electrical signal that can be amplified. Many digital disc players and streamers include an internal DAC circuit. But some people prefer to employ a separate DAC. Some devices (CD Transport or streamer) may lack a DAC and therefore provide a digital output for you to connect one of your own choosing.

Power amplifier — The circuit that actually drives the loudspeakers. Typically these come with two channels for stereo use, but single channel monoblocks are also available.

Integrated amplifier — Combines the features of the preamp control center with power amps. Some may also include a headphone output.

Tuner — A device specifically for picking up broadcast radio, typically AM and FM. These are getting rare.

Receiver — Combines the features of the Integrated amplifier with a tuner.

AV Processor — A multichannel preamp control center for home theater use. It offers input selection for audio and video, and has DACs for the main and surround channels. The more expensive ones can also perform digital EQ room response analysis and correction. Separate power amplifiers are required to drive the speakers

AV Receiver — An AV processor plus power amplifiers.