Audio Interface Tips

How to Connect a Preamp to an Audio Interface?


New podcasters usually have many questions regarding equipment setup. One of the queries they often have is how to connect a preamp to an audio interface.

A pre-amplifier converts weak mic-level signals into strong line-level signals. And an interface connects a mic to a computer. You have to connect the preamp to the mic using an XLR cable, and the preamp to the interface using a TRS cable. This connection allows for a strong and noise-free output.

To help you master the basics, I am going to talk about preamps and audio interfaces in this post.

What is a Preamp?

A microphone consists of tiny vibrating diaphragms, which produce very weak analog signals. These weak signals, called mic signals, are in the range of 0.001 to 0.01 Volts. A preamp is a device that boosts the microphone signals and brings them to the same level as the other signals in the system. A preamp inputs mic signals and outputs line-level signals.

Line level signals are what you need for your computer’s sound card to understand and play the sound. If you connect your mic directly to your computer, it won’t reproduce an audible sound. That’s where preamp plays an important role- by boosting the signals. The line-level signals are around 1 volt that is 1000 times more powerful than mic signals.

A preamp utilizes vacuum tubes or transistors to turn mic signals into line-level signals. There are in-built preamps that are a part of interfaces, mixers, or amplifiers. Otherwise, one can connect an external preamp for the same purpose.

Recommended Simple Mic Preamps

Presonus TubePre v2 Focusrite ISA OneGrace Design m101
Customer rating4.6 out of 5 stars4.9 out of 5 stars5 out of 5 stars
Presonus TubePre v2 mic preampFocusrite ISA One mic preampGrace Design m101 mic preamp
Typesingle-channelmulti-channelmulti-channel
Device classbudgetmid-tierpremium
Phantom poweryesyesyes
High-Pass Filteryesyesyes
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What is an Audio Interface?

The job of an audio interface is to connect your computer to your microphone. Audio interfaces have a D/A converter, which converts the analog signals of a microphone to digital signals. You can store, mix or edit this digital sound on your system. Now you can understand why having an audio interface is necessary for podcast recording. The audio interface has one more job- to convert digital sound into analog sound that your speakers can broadcast.

These days, when you connect an audio interface to a computer for the first time, the drivers are automatically installed. However, if you have an older version, you might be asked to download the driver and install it.

If your audio interface does not have an in-built preamp, you would need to connect a preamp externally to it before recording your podcast. Many artists also use an external pre-amp to complement the one that’s already there inside the preamp.

Here are related posts I’ve written that cover this topic more broadly:

How Does an Audio Interface Work

Connecting a Preamp to an Audio Interface

Mic, Preamp, and Interface

If you are using an audio interface with a built-in preamp, you just have to connect your mic to the interface. The built-in preamp does the same work that an external preamp set does, that is converting the mic level signals to line level. However, sometimes podcasters use an external preamp when the interface lacks a pre-built one. To connect a preamp from outside, you have to follow one extra step here.

First, plug your microphone into the external preamp’s mic input. For connecting the mic, you should always use an XLR cable to keep the sound quality high. XLR cables have one longer pin- the earth pin, and two shorter pins that carry the mic signals. The earth pin connects first, which is why you can connect or disconnect the cable with the preamp without picking external signals that create noise or distortion. This is very useful when you do a live podcast show. Additionally, the external locking mechanism on XLR wires is great for safety reasons.

Then use a TRS cable to connect the preamp into an available line input on your interface. A TRS cable is a balanced 1/4 inch cable, with a Tip (T), Ring (R), and Sleeve (S). The tip has a positive wire while the ring has a negative wire, so the opposite polarities cancel out any noise in the system. (The sleeve is the ground wire). As a result, you get a clean and strong audio signal.

Proper Gain Staging

If your mic runs on phantom power, choose that option on the front panel of the preamp. After you connect the mic, preamp, and the interface together you have to take care of the gain staging. This is a fairly simple but crucial step of setting the volume at the right level. The volume should be loud and clear so that whatever you record is audible, but it shouldn’t be so loud that it gets distorted. 

Now if your interface has an in-built preamp, it has a gain knob for gain staging. But after you connect a preamp (external) to the interface, you don’t have to use this knob. In this scenario, you have to completely turn down this knob. And then, you need to adjust the volume carefully using the input knob that’s on the external preamp. There is also an output knob on the mic that you might need to use. Just remember, you have to do gain staging just once, on the microphone.

Scarlett SoloScarlett 2i2Scarlett 18i8
Customer rating4.7 out of 5 stars4.7 out of 5 stars4.8 out of 5 stars

Podcast gear - Audio Interface - Focusrite Scarlett SoloPodcast gear - Audio Interface - Focusrite Scarlett 2i2Podcast gear - Audio Interface - Focusrite Scarlett 2i4
ConnectivityUSB Type-CUSB Type-CUSB Type-C
Mics XLR Combo124
Mic Preamps built-inYesYesYes
Ins / Outs2-22-218-8
MIDINoNoYes
OpticalNoNoYes
Max sample rate192kHz/24-bit192kHz/24-bit192kHz/24-bit
Phantom PowerYesYesYes
Direct MonitorYesYesYes
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Comparison between Scarlett Solo vs Scarlett 2i2 vs Scarlett 18i8

Benefits of Using an External Preamp

You might wonder why not skip the entire hassle and just rely on the in-built preamp. Yes, it’s convenient to do that, but there are many reasons why pro podcasters prefer to use an external preamp. Let’s discuss that more-

Superior Sound Quality – Any audiophile can tell you that the sound coming from an external preamp is way better than that produced by the in-built preamp in an interface. The external preamp has just one function, and it performs really well on that count. You get a crystal clear voice even at high gain levels. People who care about sound quality definitely invest in an external pre-amp.

High-Quality Internal Components – External pre-amps are made up of high-quality components. Their resistors, capacitors, and other parts are superior in quality. This means they add less noise to the sound, and they are very durable too.

More Features – External pre-amps come with more features like pad switches, phase reverse, etc. These features are not present on devices with an in-built pre-amplifier.

Sound Character – Many artists use a pre-amp to lend a special character to the sound. In fact, tube pre-amps are used to give a 60s style flavor to the sound.

Upgradability – Having a separate pre-amp allows you to buy a new one later if you ever want an upgrade. This is something that you can’t do with an in-built pre-amp. You can also buy a pre-amp from one brand and an interface from another if you feel that it’s going to give better results.

Connect inline preamp using 2 XLR cables

Good mic preamps are expensive. Mid-tier devices start above $400 and premium devices are often above $1000. Cheaper and much simpler alternatives are mic activators, known also as inline preamps. You simply add one between the mic and your audio interface and that’s it.

If you are using a microphone with a high sensitivity of around -50 dbV/Pa or higher you most likely won’t need a mic activator. Rode NT1-A (check current price) has a high sensitivity of -31.9 dbV/Pa while our overall top pick, a dynamic Shure SM7B has a very low sensitivity of -59 dbV/Pa. With Shure SM7B (check current price) a mic activator is a highly recommended addition.

Our favorite mic activator is Cloudlifter CL-1. Our second best choice is FetHead, which comes in 2 configurations – one is not passing phantom power so it’s safe for a dynamic mic, while other FetHead Phantom passes phantom power and is appropriate for condenser mics.

Cloudlifter CL-1FetHead PhantomFetHead
Customer rating4.8 out of 5 stars4.6 out of 5 stars4.6 out of 5 stars

Cloudlifter CL1FetHead PhantomFetHead
Best suited fordynamic miccondenser micdynamic mic
Form factorstand-alone devicedirect mic plugindirect mic plugin
dB gain added+25 dB+18 dB+27 dB
Phantom power passingnoyesno
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In Conclusion

If you have just dipped your toes into podcasting, an in-built pre-amp is good enough for you. You can get a good quality interface that has a decent in-built pre-amp. If you are using a condenser mic, this entire set-up would suit you fine. You can get an external pre-amp when you become confident about your podcasting abilities and want to spend more time and money on it. For ribbon mics, I would suggest using an external pre-amp from the beginning.

When using an external pre-amp, please remember to use the right cables when you connect a preamp to the interface. It ensures top-notch sound quality and protects your equipment from any long-term damage.

About the Author

Chris Land

I'm the owner and creator of ImprovePodcast.com, the site dedicated to providing actionable solutions for podcast creators. My goal is helping people to develop their podcasts into effective marketing and sales tools.


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