preamplifiers

Preamplifiers, often shortened to preamps, are electronic devices that amplify very weak electrical signals to a level suitable for processing, recording, or further amplification. They are typically the first stage in an audio signal chain and are designed to preserve fidelity while providing adequate gain.

Common types include microphone preamplifiers, line or instrument preamplifiers, and phono preamplifiers. Microphone preamps boost mic signals from millivolts to line level and often provide input impedance suitable for microphones, along with optional phantom power for condenser mics. Phono preamps apply RIAA equalization and adjust vinyl playback to correct the frequency response introduced by the record groove. Instrument preamps are used with guitars and basses, often providing high impedance inputs and tone controls, or serving as the front end of guitar amplifiers.

Modern preamps may be standalone units or integrated into mixers, audio interfaces, or preamp pedals. They convert very weak sources to line-level signals, typically providing gains from around 10 to 70 dB depending on type and design. Input impedance is chosen to avoid loading the source; microphone preamps typically present a relatively high input impedance to preserve mic signals, while line inputs expect lower impedance.

Quality characteristics include noise performance, linearity, headroom, and bandwidth. Good preamps minimize noise and distortion and maintain a flat frequency response within their operating range. Tube-based preamps add harmonic coloration, while solid-state designs emphasize transparency.

Important considerations include phantom power, impedance matching, maximum output level, and whether a preamplifier meets the needs of a specific source, such as a dynamic or condenser microphone, a vinyl record, or a guitar pickup. In professional contexts, preamps are chosen for noise floor, gain, and compatibility with downstream equipment.