Most current audio interfaces come integrated with mic preamps, such as the popular Focusrite Scarlett range 🙌 Generally speaking, any interface with XLR mic inputs will already be a microphone preamplifier as well! But beware – the cheaper the interface, the less inspiring the preamp, because most of these interfaces will have a pre-amplifier section simply as a matter of necessity, not because they were designed to be a great preamp in the first place 🔥 And it doesn’t work the other way round – mic preamps are not audio interfaces, and you’ll need to use one if you record to a DAW. 
Microphone signals are usually way below the nominal operating level, so a lot of gain is required, usually around 30-60 dB, sometimes even more. Guitars and basses don’t require quite as much gain, but often around 20-30 dB. Even line sources such as synthesizers may require some amplification to match studio level, because there are various standards. The old standard for home audio and semiprofessional devices is (or was) -10 dBV while professional devices operate at +4 dBu (due to different voltage references, the difference is not 14 dB but roughly 12 dB). Today, even inexpensive home studio gear is usually designed for a nominal level of +4 dBu, but electronic instruments still often work at -10 dBV or thereabouts. 
One is that you just need more preamps — perhaps your interface only has two mic preamps, but you want to record a drum kit. The second reason for adding another preamp is if the preamps in your interface are of less than optimal quality and not up to the job. You’re trying to record the sound of a field mouse scratching its leg, you have the gain all the way up, and you still aren’t getting enough level into your computer. Or you are trying to record a drum kit, your gain’s turned all the way down, and it’s still clipping. Finally, the third reason for adding another preamp is to get that magical classic retro vintage warm, liquid up-front, punchy solid, vibey 3D sound that certain preamps are supposed to have. (last modified 65 days ago by Nisa Muller from Ho Chi Minh City, Vietnam) 
You’ve heard about famous preamps such as the Neve 1073, API 312, or the REDD.47. You’ve heard they make your signal sound warm, thick, fuzzy, crispy, airy… You own an ok mic, but what you really need is an awesome preamp, right? Wrong.Many popular audio interfaces contain at least one mic preamp, and many companies claim that these built-in preamps are all you need for perfect audio. In this article, you’ll learn why an external preamp could be a good investment for your particular situation. Additionally, you’ll learn how to choose the ideal preamp, what a preamp does, the limitations of the preamps on your audio interface, and the pros and cons of plugin emulations of preamps. (revised by Timithy Esposito on September 6, 2020) 
According to the specialists at forum.cakewalk.com
, in the latest issue of Computer Music Special, “Singer Songwriter Production Guide” it illustrates a mic preamp in the signal chain that leads up to an interface. The thing is, my interface has built in Phantom power which I assumed was the mic preamps. I wasn’t aware I needed a separate mic preamp unless CM is giving us outdated or inaccurate info. I thoughtughtught an interface with built in phantom power and a mic was all that was needed. What’s the deal with mentioning the mic preamps several times in their article? They even stated their interface has phantom power, but yet use a mic preamp. So everyone with an audio interface now has to go out and buy a mic preamp?