An electronic circuit that amplifies and equalizes the analog output of the cartridge in a phonograph turntable. The output is boosted to a level equivalent to other audio sources such as tapes and CDs, and RIAA equalization is required to restore the original signal. Typically built into an audio or A/V receiver, phono preamps also come as external devices for units without phono inputs as well as for audiophiles who want the highest-quality restoration. External phono preamps are also used for turntable-to-computer applications (see USB turntable).The RIAA "Curve"When vinyl masters are cut, frequencies below 1 KHz are attenuated (reduced) to prevent the stylus from crossing over into the previous groove. In order to eliminate noise from the disc surface, higher frequencies are amplified. The phono preamp's RIAA equalization boosts the lows and attenuates the highs to recreate the original analog signal. See turntable, phono input and microphone preamp.