“Preamp,” short for “preamplifier,” can be a nebulous term, whether your goal is recording/production or live performance. While a preamp is essential for anyone who wants to get full use out of their electric guitar, microphone, or even phono turntable, chances are you may already have one. Most audio interfaces, equalizers, and mixers include some sort of built-in preamp, which does the job of most preamps you would purchase separately.
In this article, we’ll take a look at exactly what a preamp does and whether or not you actually need one.
What is a preamp?
A preamp is an important part of the signal path for microphones and certain instruments, like the electric guitar. If you’ve ever plugged a microphone into an audio interface, or an electric guitar or bass into an amplifier, then you’ve already used one. They can be fairly pristine sounding or have a lot of character for colorful recordings.
What do preamps do?
The initial signal generated by a microphone or the pickups in a guitar is low-output. It’s much too quiet to be recorded or heard in any significant way, so what a preamp does is boost low-output signals up to line level. Line level indicates the strength of an audio signal as it passes from component to component in a signal chain.
Guitar pickups are simply passive electromagnets, and microphones produce their signals by way of tiny vibrating diaphragms. Phonographs use tiny needles reading grooves on records.
None of these low-output signals are “line-level,” which is the bare minimum needed for a computer’s sound card, an equalizer, or a video camera. If you’ve ever tried to plug an electric guitar or microphone directly into your laptop, even with the right cable adapters and converters, you’ll realize the need for a line-level signal immediately.
A preamp uses transistors, or less commonly old-school vacuum tubes, to boost these analog low level signals up to line-level. Even line-level signals are not enough to drive loudspeakers. For live PA systems, you’ll need to add a power amplifier to your signal chain, too.
How do I know if I need a preamp?
Well, if you own an XLR microphone and want to record with it or use it to amplify your voice for live streaming, you’ll need a preamp. The good news is they’re already baked into basic digital recording equipment, like audio interfaces. They’re also built into guitar amps. So whether you were fully aware or not, you may already own a preamp.
Types of preamps
Now that we know what a preamp is, we can briefly discuss the different types. Without getting into the electronics and circuitry that differentiates preamps, we can lump them into three broad categories: microphone preamps, instrument preamps, and phono preamps.
Preamps for instruments
The preamp occupies a specific role in the signal chain of instruments, like electric guitars. Yet there’s usually a preamp already built into whatever amplifier you’re using. As we’ve explained, your guitar’s signal goes straight to a preamp, which amplifies its weak magnetic signals to line-level.
But this is only the beginning for the magic of guitar preamps. Good preamps built into guitar amplifiers, like this tube-driven Vox 15W model. also shape the tone of the line-level signal, adding a bit of gritty overdrive or distortion. Those add-ons prepare the signal for subsequent effects like reverb and compression before it hits the power amp and speakers.
Guitar preamps are so essential for tone that many guitarists prefer to have additional external preamps in pedal form, like the Boss Acoustic Preamp or a high-end tube-driven model by Koch. Either one can make your small amp sound like a booming Marshall stack.
Mic preamps
Guitarists love different preamps for how they shape tone coloration. They’re able to adjust highs, mids, and lows, and boost classic rock-style harmonic distortion. But mic users typically want sound quality with more transparent clarity and cleanliness.
Getting a good, clean line-level from your microphone takes some tweaking. Most performers do the tweaks with the “gain” control on a preamp, audio interface, or equalizer. Dynamic and condenser mics may need a bit less gain than weaker ribbon mics. If you turn the gain up too much on a condenser mic, you’ll wind up with distortion. And not the good kind of guitar distortion.
The gold standard for mic preamps is ample “headroom”. That’s the ability to crank up gain without deteriorating the signal into distortion. The Focusrite Scarlett Audio Interface is particularly well-known for its preamp’s headroom as it boosts mic levels for use in your computer’s digital audio workshop (DAW).
DAW audio interfaces are not the only devices that feature mic preamps. If you’re a videographer, consider a standalone, minimal mic preamp.
Phono preamps
Record players continue to enjoy a resurgence in popularity and use. Unlike mp3 players, iPhones, or CD players, which send out digital signals that are already line-level, a record player’s signal chain begins just as weak as that of a mic or an electric guitar.
If you want to incorporate a record player into your home audio system, you may not need a separate phono preamp. A quality stereo receiver may already have a phono-specific input with a preamp ready to go. But if you plan to do some DJ work and you’ll send phono signals into different effects processors, you may need a phono-specific preamp like this Rolls Bellari.
Benefits of a preamp
Once we understand what a preamp is and what a preamp is used for, it becomes clear how beneficial they are. Most importantly, a preamp makes low-level signals louder. It’s essential for recording, broadcast/streaming, and live sound reinforcement. Without a preamp, we ultimately have no useable signal.
There are tonal benefits with preamps, too. Certain famous microphone preamps, such as the ubiquitous Neve 1073, have an undeniable character that people love. The preamp section of a guitar amplifier plays a huge role in shaping the tone as well, providing things like distortion and equalization.
Preamp vs power amp: What’s the difference?
Unfortunately, line-level signals still aren’t strong enough to drive headphones or speakers. That’s where a power amp comes into play. Power amps provide a later stage of amplification, which boost line-level signals up to speaker level.
Guitar amps have a power amp section that drives the speaker cabinet, and active speakers have built-in amps. Passive speakers require dedicated power amplifiers to drive them.
Hypothetically, let’s say you have an audio interface and pair of active speaker monitors. The speakers connect to the line outputs on the interface; the speakers receive the line-level output of the interface, and their internal power amps bring it up to speaker level for amplification.
Features to look for when buying a preamp
General features to look for when buying a microphone preamp are the number of inputs, whether it has phantom power for condenser microphones, and how much clean gain it has on tap. Lower output microphones require more juice, so you want to be able to drive the signal without introducing a bunch of noise.
Next, there are select microphone preamps designed for videographers, and then there are those used for studio recording. Many preamps for videography attach to the camera itself. In terms of function, they aren’t any different than those used in the studio, though they’re more affordable and have less “mojo” than sought-after studio preamps.
Studio mic preamps usually have a color, or tone, that recording engineers like. That’s the most important feature to keep in mind when shopping for a studio preamp; does it have the sound I’m looking for? From there, you’ll be able to find the best preamp for you.
