Microphone preamps are designed to boost microphone signals so they can be recorded or amplified via a PA. Mixing consoles and audio interfaces usually come pre-fitted with microphone preamps, which can also be picked up separately when you're looking for a specific sound or timbre.
Microphone Preamps vs. Standard Amps
Microphone preamps are not to be confused with regular amplifiers. Preamps simply boost weaker signals to 'line level', while standard amplifiers or power amps are powerful enough to reproduce the sound through a speaker system. In a way, amplifiers take over from preamps, boosting a 1-Volt line signal to several tens of Volts.
Valve and Solid State Microphone Preamps
Before the invention of the transistor in the sixties, all microphone preamps came fitted with valves that added colour, smoothed out any sharp peaks and left a warm, organic sound. Transistor-preamps generally sound cleaner and pack extra punch since any sonic peaks are 'preserved' rather than rounded out. That said, there are ample solid-state classics that sound anything but sterile, in fact, the preamps made by brands like SSL, API and Neve can be overdriven to satisfying effect. While both valve and transistor preamps are widely used these days, one kind isn't necessarily better than the other - it's simply a matter of taste. Mixers and audio interfaces often feature what's known as IC preamps: integrated, circuit-based preamps designed to boost the signal without adding any colour to the sound.
Preamps with Phantom Power
Condenser microphones as well as active dynamic microphone and active ribbon microphones require phantom power. Most external preamps offer a phantom power function (labelled something like '+48V' or 'Phantom'), but if your preamp, mixer or audio interface doesn't, you can always grab an external phantom power supply. A phantom power converter that turns +48V phantom power into 5V 'plug-in' power is only required when you want to connect a clip-on microphone or headset microphone to a standard microphone preamp instead a bodypack unit.
Microphones with a Built-In Preamp
Microphones with a built-in preamp are called active microphones. While condenser microphones feature a preamp as standard, there are also active dynamic microphones and active ribbon mikes, so some active microphones will need a preamp. In practice, the built-in preamp only lowers the impedance so you can use longer cables and need less 'gain' from your mixer or interface. It's kind of like a pre-preamp. When it comes to passive microphones, a similar result can be achieved using a microphone booster, which technically turns a passive mike into an active one. Active microphones always require a power supply and, in most cases, this will come in the form of phantom power supplied by a mixer or audio interface. In addition, there are microphones available that can run on batteries, as well as fuss-free USB microphones that can be plugged directly into a computer without the need for an external preamp.
Frequently Asked Questions About Microphone Preamps
Why do I need a microphone preamp?
Before you can record or amplify a microphone signal, it needs to be boosted to line-level. This can be done using a microphone preamp. These preamps often come built into audio interfaces and mixing consoles but you can also pick up an external preamp.
Which microphone preamp should I buy?
Mic preamps made by brands like Warm Audio, BAE, Heritage Audio, Rupert Neve Designs and API offer a specific colouration of the sound - in other words: a unique timbre. A cleaner sound is offered by preamps from makers such as Focusrite, PreSonus and Audient. Before you continue your search, figure out the number of preamps you need and whether or not you want access to digital outputs.
What's a preamp?
Preamp is short for preamplifier: a specially-designed device that's able to raise weaker microphone signals to line-level for recording or amplification. Record players also use dedicated preamps, but these are slightly different phono preamps.
