This is a question I asked myself a long time ago and I assume that many of you have the same question now, so, I did a lot of research on the matter and I intend on sharing what I found out!
In this post I will explain exactly IF you need one, as well as giving you a good idea of what a microphone preamp does, how much it costs, how to use it with your audio interface, etc.
Microphones usually have low output, which means that in order to be able to record properly you need a preamp to boost their signal.
All Audio Interfaces come with preamps built into them and if you are recording at home, they are probably good enough for you.
But this doesn’t mean that you may not need an external, higher quality one, down the line.
Let’s get right into it!
What is a preamp?
A preamplifier is either the circuit within a device (Microphone, Audio Interface) or it can also be a dedicated external device that has the same circuit inside.
The objective of a preamp is to increase the level of the signal coming from the microphone, since they are usually too weak to be transmitted to a recording device with adequate quality.
The level of signal required by these recording devices is called line level. So, you could say that a preamp increases the signal to line level by also providing stable gain and reducing noise that could be harmful to the signal.
A mic preamp not only provides gain for the microphone’s signal, but it can also provide 48v phantom power for condenser microphones.
Preamps of audio interface.
Every Audio Interface has preamps built into it. That’s why they have a gain knob, to be able to increase or decrease the microphone’s signal.
Note: Most Audio Interfaces, even the inexpensive ones, have the XLR inputs in the front (which have a preamp) but also other inputs in the back which are Line-in and Instrument inputs.
The line-in is the highest signal level and doesn’t require a preamp.
It should be used when connecting a non-instrument piece of hardware (external preamp, compressor, EQ, etc.) or instruments that have a line output level (Keyboards, synths, etc.).
The instrument input is the most variable signal and does require a preamp to be raised to line level.
Here you connect instruments such as Guitars and Basses.
Benefits of a dedicated external preamp.
As I stated above, all Audio Interfaces come with integrated preamps and depending on the sound quality you are going for and also, your ability to really notice a difference between those integrated and really good external ones, you might consider an upgrade.
Having a dedicated external amp can;
- Increase the Gain level: This is by far the most important function of a preamp.
Many microphones, such as the Shure SM7B, have a very low output and often require more power than the preamp of an Audio Interface can provide. Having an external one will give you the power the microphone needs.
- Improve the sound quality: The improvement in sound quality may not be noticed as much at lower levels, but as soon as you increase the gain, like you would on low output microphones, there will be a noticeable difference.
This is because the circuitry of external/dedicated preamps is a lot more sophisticated.
- Lower the noise: Most preamps, even in budget Audio Interfaces, are actually really quiet. So, if you are recording a loud source or if you use high output microphones, there shouldn’t be any issues.
The problem arises when you are using a really low output microphone and recording a quiet source.
This is where getting an external preamp can do a big difference.
- They give character to the sound: I personally think that this is the main reason to get an external preamp, aside from the Increasing the Gain level of course.
The preamps in most Audio Interfaces sound very clean and crispy, which isn’t bad at all! But it all depends on what you are looking for, if you want a dirty tube sound you can get that by using an external preamp.
- Allows for extra Mic Inputs: Using your mic with an external preamp will allow you to the connect it to the Audio Interface. But don’t use the XLR inputs on the front of the Interface, use the Line Inputs in the back.
Note: Use XLR cable on one end (or on both if your setup will allow it) and TRS on the other. These are balanced cables (Stereo).
- Extra features: Some features that external preamps offer in comparison to most preamps in Audio Interfaces are; Phase Reverse, Low cut (High Pass).
Phase Reverse: This reverses the polarity of the signal. It’s especially useful when recording instruments with two or more mics (like snare drums). You revert the phase on one mic so that it aligns with the other one.
Low Cut: Allows for lower frequency attenuation. This helps getting rid of boominess and rumbles.
Types of preamps.
There are lots of different kinds of preamps available on the market and each of them will fulfill certain needs and have specific features. They can add color or be designed to deliver a transparent signal.
The ones that add color generally are: Tube and some Solid-State Preamps.
While the ones that fall under the “Transparent” category are: Digital and some other Solid State Preamps.
Note: No preamp type is better than the other, it all comes down to your own preferences and needs.
Many Engineers prefer the Digital Preamps because they want to capture the performance exactly the way it’s being performed, while other like to add color or warmth.
These preamps use Valves or Vacuum tubes to create Gain. They will color the sound significantly, they aren’t “transparent” like some other preamps.
Tube Preamps are known for adding warmth to the mids, especially, but also body to the bass and creating open highs.
This warmth is added when the signal increases, because tubes tend to distort the sound a bit but in a “pleasing” way. The circuit of a tube preamp also tends to create some slight compression, which adds color.
Solid State Preamps:
Transistors are great at creating gain with less heat, which means that as the gain increases, they can maintain very low distortion until they reach the maximum level. At which point the distortion will be extremely noticeable. This is also known as clipping.
Digital preamps take the analog signal and convert it to a digital signal, adding their own sonic flavor in the processing before the signal is sent to the DAW.
These preamps are useful because they allow you to bypass the Audio Interface’s built-in audio conversion which tends to be inferior.
Technically you could refer to these as Audio Interfaces, since they amplify the signal and also convert it to a digital format so that your PC can understand it. BUT their main focus is on the preamp!
These are all Microphone specific preamps, but there are also Instrument specific ones which are designed to optimize the tone of a specific instrument, such as Bass Guitar, Electric Guitar, etc.
How to use the Preamp and Audio Interface together.
I already mentioned this earlier in the post, but I’ll give you a better explanation on how and why to do it.
When using an external preamp, you don’t want to send that signal into the preamp of you Audio Interface since it will affect it.
So, what should you do instead?…
- Connect the microphone to the XLR Input on the external Preamp.
- Connect a cable either an XLR or TRS cable to the output of the Preamp.
- That same cable should be connected to the Line inputs on the Interface (usually on the back).
What is a TRS cable and why use it?
The difference between TS and TRS cables is that the TRS ones carry a stereo signal, while TS is only mono. This is because they use an extra third conductor, which is referred to as the “ring”, allowing them to carry that extra signal.
A TS Cable carries the Audio and the ground signals alone, which makes it really susceptible to noise and interference, while in a TRS (also XRL) cable you have 3 cables instead of two. One carries the ground and the other two are actually two copies of the same signal.
The cool thing about these cables is that, let’s say you sing into a microphone and the signal gets sent into the cable, the phase of one of those signals actually gets reversed.
Once it reaches the end of the cable, the polarity of that same signal gets flipped again, now being in phase with the first one.
Why is this so useful?…
Because all the noise picked up from the cable itself (outside interference) will end up being out of phase and cancelled out once it gets flipped back. Pretty cool right?
The longer the cable, the more unwanted noise it will pick up, so make sure to use XLR and TRS.
If you want a complete explanation on how these cables work, here’s a post about this exact topic.
Who could benefit from a Microphone preamp?
If I’m completely honest here, the only reason you should get a microphone preamp, especially if you are building a budget home studio, is if you have a really low output microphone that your Audio Interface can’t possibly handle.
I wrote an article about both the Heil PR40 and the Shure SM7B, both of which actually need a bit of help boosting their signal. I also mention the Cloudlifter CL-1, which will take the phantom power of your interface (make sure that it’s on) and feed it to the dynamic mic.
Preamps have a huge range of prices, but there is a common theme among all of them… none of them are actually cheap.
If you want one that can actually give you a really good performance, you’re looking at least a $300-dollar product and they can easily reach the $2500 mark.
Some good options would be the ART Pro MPA II, which is a 2 channel Tube preamp and for the price you can’t really go wrong.
Another cheaper option is the ART TPS II, which also is a 2 channel Tube Preamp. According to loads of reviews online, it is a great value.
If you are just starting out, I’d say you should forget about external preamps and actually invest a bit more in a powerful Audio Interface with decent preamps already built-in.
Even though investing in an expensive preamp might do wonders for your recordings, I don’t think it should be one of your primary focuses, since they aren’t particularly cheap.
Also, the difference in quality might not be as obvious to the untrained ear.
Note: Make sure you have great microphones (like the Shure SM7b, which really needs a preamp), otherwise you will be running a bad signal into a great preamp… not ideal.
So, if you feel you need something that improves your recording quality and budget is not much of an issue, buy one! They are worth it! But again, I wouldn’t worry about investing in a preamp until I really need to.
Hope this information helped! See you on the next one.