As can be seen from the term preamplifier, preamplifier or preamp, it is an amplifier that amplifies the signal for a downstream amplifier or mixer circuit. The reason for this may be level or impedance matching.
In audio technology, we know the microphone preamplifiers and the AF preamplifiers, which provide the level matching to the power amplifiers. They are characterized by excellent frequency response over the entire low-frequency range up to 100 kHz and by high sensitivity, which can exceed -20 dBu (Decibel Unloaded). With built-in microphone preamplifiers, these can have a sensitivity of less than -60 dBu. Decisive for the quality of LF preamplifiers are not only the gain, which can be up to 80 dB, but also the signal-to- noise ratio and the freedom from distortion.
Functionally, LF preamplifiers offer, among other things, several inputs, including at least one microphone input and high-impedance instrument inputs( Hi-Z) with input resistances of 400 kilo-ohms and higher and a line-in input with more than 10 kilo-ohms, filter functions for low-cut, also known as low-cut, adjustable gain, phase rotation for the channels and phantom power for condenser microphones.