Preamps

A preamplifier, or preamp, is an electronic device that increases the amplitude of a weak audio signal from sources such as microphones or instrument pickups to a level suitable for processing or recording. In audio systems, preamps precede power amplifiers and other gear. They aim to maximize signal-to-noise ratio while preserving tonal character. A key spec is input impedance to avoid loading the source; output is typically balanced line-level to feed next stage. Gain is adjustable, often tens of decibels.

There are several types: microphone preamps, instrument preamps (or DI preamps that convert high-impedance instrument signals to low-impedance microphone levels), and line preamps designed to boost line-level sources. They can be standalone units, rack-mounted, or built into mixers and audio interfaces.

Design approaches include solid-state (transistors, FETs), vacuum-tube (valve), and transformer-coupled circuits, each imparting different character. Some preamps prioritize transparency and low noise; others color the sound for musical effect. Phantom power (typically 48 volts) is commonly provided to power condenser microphones.

Performance considerations include noise floor, dynamic range, total harmonic distortion, and headroom. Users consider gain range, available impedance options, pad or filter features, and connector types (XLR, 1/4 inch). The choice depends on the source, desired sound, and workflow in studios or live settings.