What Is a Preamp, and Do I Need One?

Looking for ways to improve your sound? Of course you are — who isn’t? You’ve likely heard about the benefits of upgrading your preamps: the sweetening effect of classic components, the added clarity of low distortion, and the increased dynamic range of high headroom circuitry. It all sounds fantastic, right? But what does it all mean? What exactly is a preamp, and do you need one to get better sound? Here’s Sweetwater’s two cents on the subject.
What Is a Preamp?
Despite all the hype you may hear about preamplifiers, they have one fundamental job: to increase gain — taking a weak signal and boosting it up to a line-level signal. Here’s how it works:
Mic- or instrument-level signal -> Preamp = Line-level signal -> Power amp (or outboard gear)
Every time an amplifier is used in the signal path, it is referred to as a gain stage. Every gain stage boosts the volume of the signal so that it’s useful to the next device in the signal chain. For instance, that weak signal coming from the moving coil in your dynamic microphone’s magnetic field is WAY too low to run into your DAW or processing gear. To boost its voltage (get it loud enough), you need to run it into a mic preamp.

Pro Tip: Every gain stage introduces noise into your signal. Preamps feature line-level outputs, and if you run that signal into your interface’s preamps, you’ll not only add unnecessary noise to your signal, but you’ll probably also overload the input and cause the signal to distort. You’re going to want to plug that pre into your line inputs.

What a Preamp Isn’t
Let’s start with the obvious one: a preamp isn’t a magic bullet that will solve all your audio woes. In fact, a preamp generally won’t solve any problems you have with your sound — a quality preamp will let you get even more out of the good audio you’re already getting. It’s the icing on the cake, and if the cake isn’t good, even the best icing isn’t going to fix it.

Pro Tip: You can get a lot more out of the preamps you already have by being diligent about keeping the gain in the sweet spot, with the input gain just low enough to keep the signal from clipping. That will provide you with the cleanest and clearest signal you can get from your preamp, keeping your signal above the noise floor. It’s often the solution to your basic gain staging issues.

First Things First
One of the accepted truths about signal quality is that the biggest improvements in audio quality happen on the extreme ends of the signal chain. For example, here’s a basic signal flow layout:
Singer -> Mic -> Preamp -> Processors -> A-D converter -> DAW (plug-ins) -> D-A converter -> Powered studio monitors
Just as having a great singer makes everything else sound better, getting a better mic makes a vastly greater improvement in your sound than upgrading your digital converters will. So if you’re looking for the best way to improve your sound, then you’re probably better off investing in a great microphone than in a preamp. Need help finding a great mic? Don’t worry — your Sweetwater Sales Engineer will happily help you out with that.
Once you have a great mic, then it’s time to shop for a better preamp.
Types of Preamps
Got a collection of quality mics? Sporting a set of accurate studio monitors? Still need to step up your game? Now may be the time to pick up that preamp you’ve always wanted. While you can separate mic pres into more classifications than there are music genres, they can all fit into one of two categories: clean and colored.

Clean microphone preamplifiers, such as the Grace m101 or Millennia HV-3C, are designed to take the incoming signal and boost it dramatically (up to 75dB of gain in the Grace), while introducing as little coloration (harmonic distortion) as possible. Basically, you get the input source sound, and it’s loud enough to work well with the rest of your outboard gear or drive the line input of your interface. Good deal, right? Recording a clean, uncolored signal is perfect if you are doing additional processing in the box via plug-ins.

Colored microphone preamplifiers, such as the BAE 1073MP (or virtually any preamp with “73” somewhere in the name) or the Universal Audio SOLO/610, have a characteristic sound to them. This means they alter the incoming signal by introducing some form of harmonic distortion, whether through the electronics or the use of transformers. These harmonics often sweeten the sound, making it slightly more complex and allowing it to find its place in the mix more easily than a cleanly boosted signal. True, this pre-coloration will influence your future signal processing options, but these preamps sound great, and they save you a ton of mixing time.

Pro Tip: If you’re already in the market for a new preamp, then you may want to take the next step and grab a complete channel strip, such as the Rupert Neve Designs Shelford Channel or the Avalon VT-737sp. These handy boxes not only include high-end preamps, but they also come with in-line processors such as EQs and compressors. Generally each section of a channel strip imparts its own unique character on your sound, providing you with impressive ways to improve your sound.

What to Look for in a Preamp
Look at the specs for any preamp, and you’ll get bombarded with tech specs that very likely don’t mean a thing to you. You may find yourself wondering, “What the heck is THD+N Ratio?” That’s okay — many professional engineers don’t really look at that stuff anyway. Here are some of the things you really want to look for:

Number of channels — do you need one, two, eight, or more channels? Be sure to get as many as you need
Type — tube and FET preamps tend to be highly colorful, while many solid-state models (particularly transformerless ones) are cleaner and less colored
Maximum gain — while condenser mics may be fine with 30dB–50dB of gain, low-output/high-impedance mics such as old dynamics and ribbon mics typically require lots of gain (50dB–70dB)
In-line processing — the onboard EQ and compression you typically get from channel strips can be really handy
I/O — of course you need to be sure you can hook up your gear, but things like onboard digital conversion can be really handy, especially for 8-channel preamps that connect via ADAT optical

Consider the API 500 Series Format

One last shout out to the API 500 Series format. Although it’s been around for a long time, this modular platform has gained surprising popularity in the past decade as more manufacturers have adopted it. The 500 Series format consists of small modules that slide into a chassis that supplies power and sometimes I/O. The major benefit of the 500 Series platform is that each module is significantly more affordable than its standard rackmount counterpart. Ultimately, this lets you assemble a mix-and-match collection of preamps, EQs, dynamics processors, and other outboard gear in a portable and affordable format.

If you need help selecting the right preamp for your studio, give your Sweetwater Sales Engineer a call at (800) 222-4700.
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