A microphone preamplifier (or mic preamp) is one of the many things you’ll need to equip yourself with before recording anything with a microphone.
To put it simply, a mic preamp amplifies the weak signal coming from the microphone and boosts it to line level, so the audio can be recorded onto your recording device.
The sounds you record via the microphone won’t be distorted and will be loud enough to register on most recording devices.
What Exactly do Mic Preamps do?
In essence, a mic preamp works to increase the line-level while also providing a stable gain.
Using a microphone without a preamp and then trying to record will result in either very low levels of recording or nothing at all. The signal is just too weak to be usable and might end up distorting the sound so much that it becomes unrecognizable.
Most mixing consoles and recording devices won’t produce an adequate return if the mic is not connected to a preamp. But, it’s not always a simple task to find a preamp that is right for your particular mic.
Choosing the Best Mic Preamp
Choosing a mic preamp really comes down to compatibility and what kind of sound you want to get out of your mic. You have three options at your disposal:
Tube mic preamps are based on vacuum tube technology and have been around since the beginning of recording technology. Even though they represent old technology, they are still preferred by a variety of different musicians. These preamps have a built in tube which amplifies the signal.
Solid state preamps are newer pieces of technology and are transformer-based. They add less character/colour to the recorded sound and are more accurate. The major difference between the mic preamps is the distortion they add to the recorded signals.
Obviously, hybrid preamps are a combination of the two technologies.
Distortion can be a key issue in determining what preamp is right for you.
If you run out of headroom on the circuit (a condition in which the output voltage extends beyond the power supply voltage), you’re going to encounter some distortion. For the most part, the distortion with solid state preamps is not going to be pretty. Indeed, it is a highly unpleasant sound that can end up ruining a recording if you’re not careful.
On the flip side, the distortion that tube preamps cause is actually quite pleasant to the ear. It adds a natural character to the sound. It’s a big reason why many people gravitate to the older style because it’s been proven to deliver high-quality sound even at high voltages.
That being said, many musicians have certain preferences, especially if they have a choice between two high-quality options. For the most part, vocalists prefer tube preamps because the sound produced is much richer and fuller. There is also increased clarity. By contrast, solid state preamps might tend to make vocals sound thin and flat.
Musicians who play instruments like the drums or the guitar often prefer solid state preamps because they can catch each individual snare hit or guitar pluck in rapid succession. Although tube distortion can be pleasing with vocals, it often tends to garble the sound of any speedy instrumental playing.
Other Technical Considerations
This might sound like a television question, but, in fact, it describes the ability to record a certain amount of tracks.
Each preamp will have a set amount of channels and each channel will correlate to the amount of tracks one can record simultaneously. Obviously, a single-channel preamp allows you to record only one track at a time. This is ideal for those one-man bands that need to record everything separately.
There are dual-channel and multi-channel preamps that provide exactly what their names imply. But, some preamps come with a device referred to as a channel strip which provides a number of different features on top of the ability to record multiple tracks.
You’ll also need to take into account something called impedance.
This is basically a holistic measure of the restriction in alternating circuits (AC). Every microphone has its own range of impedances generally ranging from around 50 ohms to 2,000 ohms. You’ll want to find a preamp that “harmonizes” with your microphone in this sense.
If the preamp has a limited range (or the microphone’s ideal impedance output is somewhere outside that range), you’ll probably want to look elsewhere. As a rule of thumb, the mic preamp’s input impedance should be around 10 times greater than the microphone’s output impedance. So, if the mic’s output impedance is 100 ohms, then the preamp should be able to accommodate up to 1,000 ohms.
If you are going to use a condenser microphone, make sure the preamp has Phantom power to power up the mic. Condenser mics will not work without Phantom power.
How much noise is the preamp adding to the overall sound? It is very important to check this, not on the paper, but by actually recording a test audio. The preamp should be very quiet and shouldn’t have any noticeable noise even at very high gain.
As a rule of the thumb, high-quality preamps will always outperform lower quality preamps. For example, if you’re using a mediocre solid state preamp and you get a chance to switch to a better tube preamp, then you should probably do it. The same is true for the opposite. A cheap tube preamp will sound worse than a better designed solid state preamp.
Overall, finding the best mic preamp has a lot to do with tweaking it and discovering the right settings for your particular microphone.
Rajiv Agarwal is sound designer, music composer and mastering engineer. His studio Audioshapers delivers professional audio mixing, mastering and audio post production solutions.