Microphone preamplifier
A device that boosts weak microphone signals to usable line level.
Last updated
A microphone preamplifier is a sound engineering device that boosts a microphone's signal so other equipment can use it. Microphone signals are typically too weak to travel to devices like mixing consoles or recording gear without losing quality.
The preamplifier raises the signal to line level—the strength those devices require—by applying stable gain and preventing induced noise that could distort the sound. This term can refer to the internal circuitry inside a microphone itself, or to a separate device or circuit that the microphone plugs into; in both cases, the purpose is the same. Colloquially, it is called a mic preamp, micamp, preamp (not to be confused with a control amplifier in hi-fi gear), mic pre, or simply pre.
Technically, a dynamic microphone’s output voltage can be as low as 1 to 100 microvolts. A preamplifier boosts that by up to 70 dB, reaching as high as 10 volts. This stronger signal then drives equalization circuits in an audio mixer, powers external audio effects, or combines with other signals to create a mix for recording or live sound.
Beyond providing gain, a microphone preamplifier—whether built into a mixer or as a standalone component—typically supplies power to the microphone, usually 24 or 48 volts of phantom power. A microphone is a transducer and contributes much of the coloration in an audio mix; most audio engineers believe the preamplifier also affects sound quality. It can load the microphone with low impedance, forcing it to work harder and altering its tone.
It might add its own coloration, different from the mixer’s built-in preamps. Some microphones, like condensers, require an impedance-matching preamplifier to function properly. Certain preamplifiers are part of a channel strip, which may also include compressors, equalization, noise gates, and enhancers.
Quick Facts
- Output voltage range
- up to 10 volts
- Typical gain
- up to 70 dB
- Dynamic microphone output range
- 1 to 100 microvolts
- Phantom power voltages
- 24 or 48 volts
Facts from the source article.
Lore & Background
The term microphone preamplifier can refer either to the electronic circuitry within a microphone or to a separate device or circuit that the microphone is connected to. In either instance, the purpose is the same: to increase a microphone signal to line level. The output voltage on a dynamic microphone may be very low, typically in the 1 to 100 microvolt range, and a microphone preamplifier increases that level by up to 70 dB, to anywhere up 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 or for live sound.
In addition to providing gain, a microphone preamplifier as found in a sound mixer or as a discrete component typically also provides power to the microphone in the form of either 24 or 48 volt phantom power. 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. 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.
Reader's Guide
The microphone preamplifier is a foundational component in both recording and live sound, as it bridges the gap between the weak electrical signal produced by a microphone and the line-level signal required by mixing consoles, recording devices, and other processing equipment. Without it, the inherently low output of dynamic microphones—often in the microvolt range—would be unusable for further processing. The preamplifier's ability to provide stable gain while preventing induced noise is critical to maintaining signal integrity. Additionally, the preamplifier often supplies phantom power, enabling the use of condenser microphones that require external voltage to function.
The preamplifier's influence extends beyond mere amplification; it can load the microphone with low impedance, forcing the microphone to work harder and change its tone quality, or it can add coloration by introducing a different characteristic than an audio mixer's built-in preamplifiers. Some microphones, such as condensers, must be used with an impedance matching preamplifier to function correctly. As a result, the choice of preamplifier is a significant factor in the overall sound of an audio mix, and it remains a key element in the signal chain for both professional and project studios.
More in Headphones, Mics and Mice
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Microphone preamplifier (CC BY-SA 4.0).
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced