In short a Microphone Preamplifier is a device used to amplify the voltage from a microphone, which is extremely low, and increase it to a level that is usable for recording or live sound.  This acceptable level is commonly referred to as line level also known as +4db.

There are many different methods employed to achieve this voltage amplification that is performed inside the microphone preamp and each one has an impact of the signal or sound quality that is a result. Many microphone preamps are vacuum tube based, transformer based, or even based on transformer less op amp designs. Some mic preamps even use a combination of technologies and offer the ability to switch transformers in and out of the signal paths needed. Each design has it own use and is a personal choice as to which sound is preferred.

The Micphone signal can never be improved upon rather it can only be degraded by the least amount, Which is why Class A equipment made only with the highest quality components are so highly sought after. The desired effect is to bring the microphone level up with the least amount of noise, static,  and unpleasant coloration as possible.

Many audio interfaces come with preamps built into them but they are created with cost savings in mind which often produces and inferior flat sound that is dull and lifeless. These differences may seem subtle to the untrained ear or when compared with an inappropriate monitoring source (such as head phones or a stereo system). Once multiple tracks are recorded with different instruments and all are played together the subtle differences become night and day transformations and each tracks dull and lifeless sound becomes amplified by the next track. This is the primary reason many home recording enthusiasts become discouraged and are unhappy with the results they achieve. By purchasing a professional quality microphone preamp they are in effect lifting the veil from their music and sound quality.

Originally Microphone Preamps were confined in large mixing consoles made by such companies as Neve, Amek, Api, Focusrite and others. As digital recording has become more prevalent the need for stand alone high quality microphone preamps has also increased. Many companies offer great class A equipment these days for much less than the large mixing consoles. These external mic pres come in a number of different channels or number of preamps for simultaneous mic recording. Common configurations include single channel, 2 channel (dual), 4 channel (Quad), and 8 channel preamps.

With the ability of over dubbing, just 1 single channel botique microphone preamp is needed and each and every track that is recorded from vocals to guitar to bass can all benifit from the superior sound quality of that preamp.  Purchasesing a nice used microphone preamp is almost always a better decision than buying an equally priced new unit. One can often score deals on vintage equipment that has been restored or mixing consoles that have been parted out and racked into dedicated preamps.

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