Microphone preamp

Microphone preamp (Microphone preamplifier) (is a preamplifier used to increase a microphone's low output voltage to a stronger, more usable level. A microphone preamplifier must provide stable gain for small signals without being sensitive to induced noise from cabling and without distorting large amplitude signals. Some microphones must be used in conjunction with a preamplifier to function properly.

A microphone is a transducer and, as such, is the source of much of the coloration of an audio mix. Most audio engineers would assert that a microphone preamplifier also affects the sound quality of an audio mix. A preamplifier might load the microphone with low impedance, forcing the microphone to work harder and so change its tone quality.
A preamplifier might add coloration by the nature of its electronic circuitry. Different combinations of microphones and preamplifiers can achieve a wide range of tone, character and mood. Microphone preamplifiers come in many shapes and sizes, and vary greatly in price from a few dollars to many thousands of dollars. Most audio mixers have microphone preamplifiers built in. External preamplifiers are available for adding a different characteristic than the audio mixer's built-in preamplifiers.

Some preamplifiers exist as one part of a channel strip, which can include other kinds of audio recording devices such as compressors, equalization (EQ), noise gates, and enhancers.
Technical details
The output voltage on a dynamic microphone may be very low, typically in the 0 to 100 microvolt range. A microphone preamplifier increases that level by up to 70 dB, to approximately 0 to 10 volts. This stronger signal is used to drive equalization circuitry within an audio mixer, to drive external audio effects, and to sum with other signals to create an audio mix for audio recording and for live sound.