Microphone preamps are an essential piece of equipment in any recording studio. They’re also used to boost signals from other audio sources, like a guitar amp or turntable. Microphone preamps amplify low-level voltage from a microphone and send it to the power amplifier to drive loudspeakers, headphones, or other electroacoustic transducers.
Preamplifiers do more than increase sound levels; they can add coloration to the signal as well. In this article, I will discuss what a microphone preamp is and how it works. I will also cover some of the various types of microphone preamps and their benefits.
What is a Microphone Preamp?
A microphone preamp is an audio amplifier that boosts the low-level voltage from a microphone to the level needed by a power amplifier for driving loudspeakers, headphones, or other electroacoustic transducers.
Basically, it takes the tiny signal from your mic and amplifies it so you can hear it better when recording in a studio with proper equipment. Unfortunately, if you don’t have a preamplifier, your signal goes straight into the mixing board, which has serious limitations on how much input is possible.
A good preamp should be transparent at least up to its highest gain setting; contribute no noise of its own unless that noise is part of the desired sound; react quickly and accurately to control signals (tuning, volume); never change the sound of the input signal, and have relatively high input impedance.
How does Microphone Preamp work?
A microphone preamplifier boosts a weak microphone signal to line level, allowing you to connect it directly to the mixer or other recording device without requiring an audio console with balanced inputs designed for use with professional microphones connected by XLR or 1/4″ cables.
Preamps come in both analog (tube or transistor) and digital varieties, although most of them are based on transistors. Some offer additional features like pads, filters, delay, and reverb effects tailored to specific applications. The following are some common types of microphone preamps:
- Solid-state preamplifiers
- Tube preamplifiers
- Active direct boxes (“DI” or “Direct Injection”)
- Condenser pad/filter boxes (sometimes called ‘preamplifier boxes’ or just ‘pads,’ and sometimes with a built-in compressor function as well).
Benefits of Microphone Preamplifier:
A high-quality condenser microphone requires higher input voltages than those that are typically available from mic-level outputs on your mixing console. This means that you need a mic preamp to boost the signal from your mixer or another recording device up to line level.
You will also benefit from using a quality microphone preamplifier if you have sensitive microphones that are prone to be overloaded by strong external sounds like air conditioners, traffic, nearby conversations, and loud music in bar and discotheque settings.
A good bit of extra gain can keep those levels where they belong without distortion or clipping. This is especially true when recording quiet sources such as an acoustic guitar.
- Microphone preamps can boost the signal from a microphone to overcome noise
- A good quality mic preamp should be transparent at least up to its highest gain setting; contribute no noise
- They are useful if you have sensitive microphones that are prone to be overloaded by strong external sounds
- A microphone preamplifier is useful in the recording studio and live sound applications, especially in situations where there is a lot of background noise or other sounds that could overload the microphone
Difference Between A Preamplifier And An Amplifier
While it’s true that a preamplifier boosts the amplitude of an audio signal, its purpose is not to generate loudness. Instead, it ensures that the amplification process doesn’t change the nature of the source sound at all—not even with gain settings as high as 20 or 30 dB.
In contrast, an amplifier performs additional operations like filtering and equalization to make a source sound louder without altering its basic character. In short:
- A preamp (microphone) increases voltage before amplifying the signal
- An amplifier (speaker) increases power after boosting voltage
For example, if you connect a microphone directly to an amp through one of its inputs, you should notice no difference in volume or tone. The same goes for a mixer input with the proper preamp—the mix should sound the same as before.
What is Microphone Preamplifier used for?
The main function of a microphone preamplifier is to make up for any volume loss caused by long mic cables and increase the signal to line level so that you can connect your microphones directly into your audio interfaces without using an external preamp. This way, you don’t have to be concerned about balancing levels between channels during recording.
This also eliminates noise, distortion, and hum when using long mic cables in live performances such as speech or vocals at weddings and parties. Moreover, it provides more headroom on the console output if you are driving long cables to a PA system where the levels can be set too high at times.
A quality preamplifier will also have an input pad that you can use if your microphones need lower gain or are susceptible to overload from external sounds like air conditioners, traffic, nearby conversations, and loud music in bar and discotheque settings. If the preamp has an output pad, it goes towards making up for any extra level loss caused by long cable runs between the console and mixer.
Common Mistakes To Avoid When Using Microphone Preamps:
Many people assume that they should buy any microphone preamplifier if their mic cables are too short or too thin, which would solve their problems. However, this is not always the case.
If you think about it, there are actually two ways that a microphone can be overloaded:
- First, by too much voltage in the first place, such as what happens when you connect the output of an external preamp to line-input on your audio interface or mixer
- Second, by too much power, applied to it, such as when you overdrive your recording console’s input stage into distortion
Do I need a mic preamp if I have a mixer?
The first point is a big problem for churches, discotheques, or other places where the sound engineer can’t control ambient noise levels, and there is no isolation with a booth.
A live mixer solves this issue because its inputs are designed to accept several types of microphones without extra amplification—such as acoustic guitars, electric guitars, vocals, and drums.
The disadvantage is that you have to match gain levels when mixing different channels, which may be difficult in situations like speeches where the participant’s voice volume varies greatly from one second to another.
A better solution would be an external microphone preamp with adjustable input sensitivity plus an output pad for running long mic cable runs. This way, you can get higher-quality recordings by not having to worry about overloading the inputs on your mixer.
How to Choose a Mic Preamp?: Buyer’s Guide
If you’re buying a microphone preamp, consider it for the following features:
Inputs and Outputs
- Number of Inputs: This refers to how many microphones you can connect to the preamp without using an external mixer.
- Outputs: The number of outputs dictates how many channels you can send through your audio interface at once. It is very convenient if you have a few sources or headphones that you want to monitor (for example, backing vocals).
Input and Output Levels
Most preamps output a balanced (XLR) signal, but some may be unbalanced RCA connectors instead. Ensure that they are compatible with your recording equipment and cables so that you don’t have any unpleasant surprises after running long mic cable runs in live applications.
You should also check the input sensitivity of the microphone preamp because if they are too high, your microphone will get overloaded.
Tube Preamp vs. Solid State Preamp
A solid-state preamp is a lot less expensive than a tube preamp, and they usually sound better as well. It’s also more reliable because there are no tubes that might blow out over time, which means you save money in the long run when you don’t have to replace faulty equipment.
However, some people prefer tube preamps because they feel like they get better results on guitars or vocals that need some colouration from the tubes to sound right. But, again, this is just personal preference – it all depends on what your needs are as an artist or engineer.
Hybrid Mic Preamps
Many of the preamps that are on the market these days have both tubes and transistors. These devices provide tube-like warmth plus all of the reliability of a solidly built solid-state circuit. This is because even if one or two tubes go bad, they can be replaced without having to change out an entire vacuum tube when just one drops out.
Single-channel, Dual channel, or Multichannel Mic Preamp?
A single-channel preamp has one input with its own level of control. A dual-channel preamp has two inputs, a pair of knobs to adjust them individually and a switch in the middle so you can choose which one is active at any given time.
Single and dual-channel preamps are much more affordable than multichannel ones, but if you want more setup flexibility, then multiple channels might be for you. There is no general rule about how many channels you need because it depends on your recording needs. Still, if you know that you’re going to want multiple tracks during most sessions, it will probably make sense to get something larger like this now instead of upgrading later.
Mic Preamp Features
Here are a few of the features that you might want to check out when you’re comparing microphone preamps:
Built-In Microphone: It’s not going to be practical to have one around all the time, but at least it gives you an idea of what each preamp sounds like. They can perform differently from one another in some cases, so it is better to know this upfront instead of having to guess. Most high-end preamps have them.
Adjustable Input Impedance: If you know your mic has low impedance, then adjust it accordingly, or if your mic has high impedance, then make sure that the input impedance is set just right for optimal sound quality. This feature isn’t commonly included in preamps, but it’s a fantastic feature to have if you can get one.
Adjustable Low Cut Filter: This filter is great for eliminating low-end rumble (plosives) and hissing noise that emanates from air conditioners, fluorescent lights, etc. Deactivating the filter will capture more detail in your recordings, but you should always try to avoid unwanted noises as much as possible by keeping these things out of the recording room.
Conducted Emissions Filter: If you’re picking up on 50 Hz or 60Hz hum from nearby electrical equipment, then this filter will help isolate your audio signal so it won’t be affected at all.
Impedance Matching Pads: Match signals with different impedances by using pads. This is helpful if you have a signal with an impedance over or under the system limit.
Adjustable Gain: Some preamps have a gain control knob for fine-tuning while others might not. If they have it, then all of your levels will be as accurate as possible, but if not, then your recordings might end up being quieter than intended when played back on other devices with different volume settings.
Phantom Power: Phantom power supply allows condenser microphones to operate on a higher voltage than is normally available from their batteries, which helps them achieve their excellent sound quality characteristics and improves transients in the audio output.
5-way Channel Mixer: A bonus feature allows adjusting signals to reduce noise interference and distortion dramatically without sacrificing warmth or quality.
Low Noise High Performance: Great for recording vocals, guitar cabs, and many other sources that can produce a lot of noise. This feature ensures that you will capture all of the output from your instruments while preventing them from being over-amplified due to background noises.
Power Source Selection: Some preamps can be powered by a battery and others by an AC adapter. Choose which one is best based on how mobile you plan to be in the studio. For example, if it’s going to be hooked up 24/7, then you might prefer DC power instead of using batteries because they generally last longer and are not susceptible to failure as often as alkaline batteries do.
Direct Microphone Input: Connects directly into the amp, which removes the need for an additional DI box.
Output Impedance: Most should say “high impedance” (10k) or “low impedance” (500-600 Ohm). Low impedance is usually better if you’re using a microphone to record an instrument because a mic needs less power than speakers do to get louder. This means that you won’t be overdriving your preamp as much when recording guitars’ other instruments.
Good Quality Faders: Some of these contain resistors that deteriorate with repeated use, so look into the overall durability of each one before settling on it.
Ground Lift Switch: If you have multiple microphones connected via their XLR cables, then there might be interference between them. A ground lift switch can help prevent this by essentially eliminating the Earth connection between your various channels so that you can keep them isolated from each other more effectively.
6-8 analog inputs: This will allow you to connect various devices like microphones, guitars, keyboards, and even DJ mixers. The number of digital inputs shouldn’t affect your decision because most modern-day preamps have them anyway.
Integrated Headphone Amp: It’s unnecessary, but it is very convenient for monitoring what you’re recording or mixing as it saves space if you don’t need to use headphones with another device in the control room.
Best Microphone Preamp
Here are some of the best microphone preamp on Amazon
Now you know enough about microphone preamp to make a great and informed decision like any smart audio enthusiast should. As always, feel free to post your questions or comments below, as I am more than happy to help out anyone who might need advice when it comes to picking one of these for themselves.
If you do have any other suggestions, please let me know about them in the comments to help out even more people with their research! Again, thanks for checking this article out; stay tuned for our next guide.
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