Mic Preamps Explained: What is a Mic Preamp?

pre ampIf you’re just starting to get into recording, you’ve probably heard or read that a mic preamp is the key to increasing the quality of your sound. Now it’s time for you to understand why and begin navigating the options. Microphones are notorious for low-voltage output, often in the range of 1-100 microvolts. The problem is that the signal level is too low for the next pieces of equipment that need to work with the sound, such as a mixing console or recording device. A microphone preamplifier (also called a mic pre) is a device used to boost the signal coming from the microphone, increasing its level to one that can be processed by a variety of equipment. The usability threshold is called line level, so the ideal mic preamp boosts the mic signal to line level while at the same time minimising any additional distortion from its own noise or other factors.

As with many other pieces of sound equipment, you have to pay a premium price for the most amazing, mind-blowing quality. Luckily, there are less expensive options that will serve many people just fine. In this article, though, I want to focus on the different kinds of mic preamps, their features, and what it is they can actually do beyond just boosting your mic levels.

Pre Amp Starting Kit

People who are dead-set on professional-quality recording are going to spend big bucks on several different pieces of equipment, including a preamp, a converter, and audio interface, and of course the microphone(s). You could easily drop a good $10,000 dollars just on that stuff. If that makes you want to flee screaming, there are plenty of workarounds that are a lot cheaper.

You can actually get really great results with even a mediocre preamp or a fairly standard consumer interface that serves as a preamp as well. An audio interface is the piece of equipment that bridges the analog-digital divide. Your microphone is probably producing an analog signal, and if you want to use your sound in the digital environment (i.e., your computer), an audio interface is the missing link. The idea with an audio interface is that you can plug all sorts of things into it, including microphones and instruments. It allows your computer to handle sound at a much higher quality that it could without the interface. Your computer will typically have just one audio input port, when you might need several more options, which is exactly what an audio interface can do.

You can get an audio interface that has the mic preamp capability built into it, effectively taking care of two different audio needs with one piece of equipment instead of two, but you’ll be even better off if you can invest in a decent mic preamp as a standalone. Whichever plunge you decide to take, you have to be willing to put the time and effort into getting the levels set just right. Be vigilant about the quality of the recording environment (reducing ambient noise and the room’s tendency to reflect sounds) and experimenting with different placements of the microphone in that environment and in relation to the vocalist or instrumentalist. Once you’ve taken care of those environmental factors, then you can spend time experimenting with different gain settings and trim levels until you get the kind of sound you’re looking for.

Number Of Channels

One of the basic choices in a mic preamp is to go for either a single or dual, referring to the number of channels it can handle. If you’re only recording a vocal or solo instrument, then a single will do. If you want to simultaneously capture two vocals or a vocal combined with an instrument, or two instruments, then the dual preamp is the one you want, although it comes at a higher cost. And of course there are multi-channel preamps with more than two channels that cost even more.

Pre Amp Important Features

Now, what about the features? This is important to sort out because they range from “none” to “more than you can make sense of.” The absolutely most simple of all mic preamps are those that just provide the phantom power needed to boost the signal from the microphone. That’s the most basic feature of all. The boosting of the mic signal is called applying gain. Ideally, it does this without adding any of its own “noise” in the form of a hum or other distortion. If a mic preamp sucks, you’ll know it as you turn up the gain all the way to 60db and hear a lot of internal hissing. You want an absolutely minimal amount of this hiss. This is the one problem with units that are doing double duty as mixers and preamps – they can pick up noise from other parts of the system. A good preamp will also reveal other environmental sources of noise by amplifying them, and then you can go ahead and do what it takes to eliminate or reduce those environmental factors. And that phantom power feature is a must if you’re using condenser microphones, which you can read more about in articles on this site. Some condenser mics operate on batteries and won’t need the phantom power. Dynamic mics also usually do not require phantom power. Make sure you preamp supplies 48v of phantom power – if it only supplies 30v, it might not be enough to properly power your condenser mic.

Read our Reviews of Condenser Microphones Under $100

Yes, you can get preamps with all kinds of other features, such as peak-stop limiters, compressors, eq, de-essers, various filters, scoopers, harmonics shifters, and on and on and on. But all those extra features come at extra costs that you can avoid by keeping it simple. With these basics in mind, you’re ready to read my reviews of a few great mic preamps you can get for under $500 that will get the job done for you.