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microphone preamp

An electronic circuit or stand-alone device that boosts microphone input. A mic preamp is used to adjust the volume of the signal sent to powered speakers or an amplifier. Unlike a phono preamp, there is no standard equalization stage, although there may be a gain control to balance different inputs to the same level. See phono preamp.

Single-Channel Mic Preamp
Because microphones have different output levels, the GAIN dial is used to balance various inputs so that the OUTPUT volume will always be the same. At the very left is a high impedance (Hi-Z) input port, typically for a guitar or bass instrument. (Image courtesy of Warm Audio LLC,

phono preamp

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.

High-End Phono Preamp
The PH-1 from Grado Labs is used by audiophiles to restore the frequencies in the vinyl record as close to the original as possible. As is evident from the jacks on the back, a phono preamp does a straighforward job: signal in - restore - signal out. The power supply connects to the four-prong jack, and the turntable is grounded to the post in the middle. (Image courtesy of Grado Laboratories,

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