The purpose of a preamp is to amplify a weak signal to a linear level, that is, a standard level of recording systems. There are two types of preamps: a circuit inside larger equipment (for instance, audio interface) and an individual device. Therefore, the availability of a preamp is critical for the smooth operation of any microphone, but it is not obligatory to buy a separate unit.
This article overviews the main features of external devices.
Improving sound quality
This bonus is most noticeable with high loudness. Often, built-in circuits sound good at 40-50 dB. But the sound worsens noticeably if loudness is increased. High-quality external preamps have more complex amplification schemes and cope well with the whole loudness range.
Embedded preamps rarely can ensure gain higher than 60 dB. 70 dB or more may be needed for many dynamic microphones, while condenser models have a large output and level the discrepancies between built-in and external models.
Built-in preamps often have a good level of a useful signal in comparison to noise. At the same time, if you record quiet source and/or use a mic with small output, external devices would definitely ensure a better result.
Changing sound character
This is probably the most common reason for buying external equipment.
As a rule, internal preamplification schemes provide a sterilely pure signal. At the same time, specific types of sound “coloring” are often viewed as an important part of audio recording.
“Dirty” tube preamplifiers characteristic to the 60s or smooth “vintage” sound of the classic 70s transistor devices – all we have heard these terms and should admit that they make sense.
Providing advanced features
External models usually have advanced functionality compared to built-in options. The most common additional functions are phase change, low cut, as well as gain step switch (pad).
Therefore, do not cut corners on the best microphone preamps. They would improve your musical experience tremendously, especially if you are a professional singer or work in your own recording studio and want to create top-notch audio products.