A turntable amplifier, also referred to as a phono preamplifier, is a unit that goes between a record player and a preamplifier or an integrated amplifier. This device amplifies the weak signal from the turntable to be equivalent to a line-level signal like those produced by CD players, DVD players, and cassette decks. Since outputs from record players also have a very treble-heavy output due to Recording Industry Association of America (RIAA) equalization, a turntable amplifier will adjust the tonal characteristics of the signal to make it more accurate.
Before the popularization of the cassette tape and the CD player in the 1970s and 1980s, long-playing (LP) records were the primary source of recorded music. They were disks of vinyl, 12 inches in diameter, that contained a groove representing the waveform of the music. A needle rode in the groove and transmitted the signal by moving between magnets in the turntable's cartridge. The turntable then sent this signal to the rest of the stereo system which had a built-in turntable amplifier to bring the signal to line-level.
Record players presented a challenge in addition their low signal levels. To effectively master an LP record, sound engineers needed to keep the wavelength represented by the groove roughly the same size regardless of what frequency it represented. Since treble signals have smaller wavelengths than bass signals, engineers invented the RIAA equalization curve. This made treble signals significantly louder so that they would take up more space in the groove while making bass signals significantly quieter, taking up less space in the groove. Turntable amplifiers also had circuitry built in to reverse the RIAA equalization, returning bass and treble to their proper levels.
As the popularity of LP records faded out at the end of the 20th century, manufacturers stopped building a turntable amplifier into receivers, integrated amplifiers, and preamplifiers. Listeners who want to continue playing LP records now need a separate device to both amplify the signal and to remove the RIAA amplification. These devices are frequently small boxes with a pair of phono jacks as an input from the turntable, a pair of phono jacks as an output to the preamplifier or receiver, and a power cord. Once connected to a turntable and to a modern receiver or preamplifier, they bridge the gap between the Edison-invented phonograph and today's high-tech audio equipment.