Do Condenser Mics Need a Preamp?

Hack the sound quality for a better understanding of how a preamp works.

A condenser microphone typically records the sound signal at about -60 to -40 dBU, which is not loud enough in terms of signal level for recording instruments. It requires amplification of the signal so the recording instrument can identify different frequencies and reproduce the results, which is carried out by a pre-amplifier, also known as a preamp.

Without a microphone preamp, the mic signal cannot be augmented to a line-level signal, which is what most studio equipment is designed to work with.

You can either get a dedicated preamp or an interface to provide the gain to mic-level signals, both of which have their own benefits and disadvantages. We’ll get into their details later on, but let’s first discuss;

Why Do Microphones Require A Gain In Signal?

A microphone converts sound waves into electrical signals, which are then transferred to different equipment for further processing. However, the intensity of the electrical signal recorded by the microphone is weak, which cannot be identified by the other equipment in the studio. The signal must be amplified to line level, which starts at about -10 dB, for other audio gear to function appropriately.

The difference between mic level signals, which typically fall in between -60 to -40 dB, is compensated by an external device called a preamp. Using a preamp does not meddle with the frequencies but only boosts the voltage of the signal so it can be identified easily.

How Does Mic Preamp Work?

A microphone preamp is made up of several electrical components, including transistors and vacuum tubes, which require power to work. These components use external power to boost the electrical signal coming from the mic, which is then sent to the amplifier. The point where the preamp amplifies the signal is also known as the gain stage because it increases the signal for the next device in line.

That said, it is important to remember that each gain stage imparts loudness into the signal, and if a preamp goes through a preamp interface, it will double the loudness, causing distortion in the sound. Thus, you must plug the preamp signal into the line and not to any other device that amplifies the signal.

Mic Preamp Vs. Phantom Power For Condenser Microphone

Preamp is often confused with phantom power, mainly because both provide voltages to the microphones, but their functions are entirely different from one another. Condenser mics require phantom power because their circuitry requires external power of about 24-48V to work.

In simple words, phantom power essentially turns the condenser mic on. Whereas, a mic preamp ensures the signals it transmits can be read by other devices.

Microphone Preamps: Dynamic Vs. Condenser Microphones

Almost all condenser microphones require phantom power and a preamp, whereas most dynamic microphones only require a preamp. The signal recorded by dynamic microphones is even lower than that of condenser microphones, meaning it requires more gain from the preamp. In contrast, their circuitry does not need phantom power to work.

Some dynamic mics, especially those that offer USB connectivity or a plug-and-play option, have built-in preamps, so they do not require external pre-amp devices to boost the signal for recording devices.

Types of Mic Preamp

Principly, the two types of mic preamps have different circuitry and applications from one another. These include;

Tube Preamps

Tube preamps use thermotic tubes, also known as valves, to produce a gain in sound. In addition to increasing the voltage level, such preamps also modify sound quality to a certain degree. They add a deep bass, airy high and a certain flavor to your line level signal.

These preamps also improve the depth of sound, especially in mid-notes, because the tubes experience a mild distortion owing to loud volume. The distortion is gradual and reasonable in magnitude, ensuring you get a perfectly audible and pleasing sound.

Tube preamps also impart color to the sound because of the natural compression owing to their circuit designs. While ordinary ears may miss it, audio engineers aspire to bring the completeness it provides to their sounds.

You can also use tube preamps as low-pass filters to reduce high-frequency notes and smoothen the high distortion. Such preamp designs are usually preferred by sound engineers and studio owners for recording vocals.

Solid State Preamps

Solid-state mic preamps are typically used when you want transparent sound, such as while working with instruments like acoustic guitars and drum kits. Unlike tube preamps, these do not add any color or flavor to your sound and keep it as transparent as possible. It is because of the transistor in the circuitry, which operates in a consistent manner as the gain increases, thereby reducing distortion.

The only downside to solid-state mic preamps is the production of odd harmonics, which are not as pleasing as the harmonics of tube preamps.

While these are the two basic types, there are subtypes within them. You can get a preamp tailored for your purpose. There are preamps designed to improve vocal and instrument quality, and there are even preamps designed specifically for different instruments to ensure studio owners get the best possible sound quality from their microphones.

How To Use Preamp and Audio Interface Together?

If you decide to get external dedicated mic preamps, you will most likely have to use it with your existing audio interface. While doing so certain precautions are required to ensure your sound is not overly amplified. 

You must always connect line outputs to line inputs and the mic input to the microphone preamp output. If you plug an external mic preamp into your audio interface, you will have to ignore microphone interface inputs and plug line output directly into line input. Failing to do so will increase distortion as the signals will be amplifying at two different points.

It does not render your interface’s mic inputs useless for those who need a mic because it allows you to expand your recording studio setup. It will come in handy during music production as you can connect the mic of the main vocalist with a dedicated mic preamp and use the interface’s inputs for instruments and backing vocals.  

In essence, you will use dedicated mic preamps for your primary sound, while the other inputs on the audio interface can be used for supporting elements while producing music.

Benefits of Dedicated Microphone Preamp

Using an external mic preamp will offer a number of benefits, which will reflect in your overall audio production. The most important of them include;

1. Improved Gain

Some condenser mics, such as Shure SM7B, require more gain than what a budget audio interface can offer, warranting a dedicated mic preamp for best results.

2. Low Noise

Using a low-output mic to record quiet signals often introduces noises to the signal, which can be fixed with a good preamp.

3. Extra Mic Inputs

Using a dedicated mic preamp frees up ports for those who need a mic and other microphones in the audio interface. You can get another condenser mic to complete your studio setup.

4. Sound Coloring

The sound coloring induced by tube mic preamps allows you to experiment with different techniques to get the best results from your condenser mic. The depth produced by such a preamp also improves the quality of vocals.

Frequently Asked Questions