2143443898_5c1e3c9f6d.jpegAfter posting the review of the Presonus Eureka, several of you asked me how to exactly connect an external preamp to an audio interface.

While this may seem simple enough, a lot of home studio owners are doing this wrong. It’s not the end of the world, don’t worry. However, you need to know the proper way to connect these things, since it might adversely affecting the quality of your recordings.

Mic Input vs. Line Input

What is the purpose of a preamp? Why does it exist? As I mentioned in Intro to Preamps, microphones produce a very low-level signal. Without a microphone preamp, the signal remains unusable.

A microphone preamp amplifies the signal from mic level to line level.

Most audio interfaces include anywhere from one to eight preamps. The inputs to these preamps are 3-pin XLR connections. You simply connect the microphone directly to the preamp via the mic input.

Most interfaces also include a number of line inputs. These accept line level signals.

Line level signals don’t need to be amplified by a preamp. They are already at the appropriate level.

Examples of devices that produce line level signals:

  • Microphone preamps (more on this below)
  • Compressors
  • EQs
  • Rackmount effects units (reverbs, delays)
  • Mixers
  • Keyboards
  • CD player/recorders

Connection Clarification

There are essentially 4 types of connections you’ll deal with in your studio: XLR, 1/4″ TRS, 1/4″ TS, and RCA. Any of these can be line inputs.

XLR and TRS are balanced connections. Most line inputs on audio interfaces are 1/4″ TRS connections.

TS and RCA are unbalanced connections. (More on this another day.)

Here’s the tricky thing. Mic inputs are also XLR connections. You can see how this could easily get confusing.

Hooking Things Up

Here’s a general rule of thumb: Connect microphones to microphone inputs, and connect line outputs to line inputs.

Let’s take the Presonus Eureka, for example. It has an XLR mic input, and that’s where I connect the microphone (obviously).

The Eureka also has both XLR and TRS line outputs (you can use either one). The back of my 003 has XLR mic inputs and TRS line inputs. Which should I use for the Eureka?

Answer: One of the TRS line inputs.

So, I use a standard 1/4″ TRS cable to connect the line output of the Eureka to one of the line inputs on the 003. If I wanted to, I could a cable that has an XLR female connector on one end (for the Eureka’s XLR output) and a TRS connector on the other (for the 003). Either one of these would work.

Line Output + Mic Input = Trouble

A lot of people run the line output of their microphone preamp into the mic input of their audio interface. This is unnecessary, because you’re essentially running the signal through two microphone preamps. This can result in distortion and a degradation of the sound.

I recently saw someone post on Twitter that they tried running their preamp to the line input instead of the mic input, and that it made an amazing difference.

It’s true, using the proper connections and gain-staging is very important when recording. Go check your rig and make sure you’re connecting everything properly.

Did this help? Got questions? Leave a comment.

[Photo by jennie-o]

  • Enrico


    Thanks a lot for the article.
    I have a Studiolive 16.4.2 and a Manley Force. Today I tried to connect it with a xlr trs cable to the line in on the StudioLive but it wont work. If I put the TRS cable half way into the Studiolive Line In I get a signal but the quality is really bad. Do I need a different cable? If I plug in my UA 6176 into the StudioLive it works perfectly with exactly the same cable.

    Thanks for your help.



  • tyra

    I just bought a focusrite solo interface and a baby blue bird microphone for studio use but I’m not sure which preamp is good for me? I’m also going to be using FL studio 11 as my DAW, can i get some suggestions?

    • http://www.homestudiocorner.com Joe Gilder

      How much time have you spent using the preamp on the focusrite? I’ve not used it, but it might sound great.

  • Zeph

    I have a question… I know this is a rather old feed though.

    I have a preamp with only XLR outputs. And the only way to bypass the preamps in my interface is by going in with TRS. Should I really just get a XLR to TRS cord? Or should I use a direct box? Or are those both terrible ideas and I should figure something else out? Thanks for the help :)

    • Kamp

      Get an XLR to TRS cord. Double check your interface’s manual for using the XLR inputs. I don’t have much experience with interfaces, but i do with mixers. most have a switch (sometimes called PAD or mic/line) to select between mic and line level signals for the XLR socket. Others have a gain control with additional resistance for a line input at the socket.

      Hope that helps!

      Additional, but probably unnecessary info: The mixer I’m using at home also has a switch on the back next to the XLR main outs to switch between mic level and line level output for when it’s used as a mic monitor mixer (TRS line-level main outs for the monitors) while sending mic-level signals to the main mixer via the XLR main outs.

  • Hagensen

    Hello, I have a problem. First of all, I want to start by saying that I am not a sound engineer, I am a voice over talent who recently is planning to go into the VO bussiness very soon. But I have a problem with my recording setup, namely that I get some sort of electronic buzz on my recordings. I am sitting inside a whisperroom that is treated with acoustic froam, I record through a Neumann U87 and I’m using an Avalon 737 preamp. Now, my interface, wich I believe is what causes the problem, is a Yamaha MG10XU mixer that has a usb connection and also works as an interface. However, I think its the yamaha that is causing the buzz, but I’d like to know what you think? Should I ditch it and get a proper interface that can be used for the sole pupose of being in a chain like this? Are there any good, quiet interfaces you can recommend that doesnt cost way too much? Or is it just that I’m doing something wrong in my ignorance and that whatever is causing the buzz is easy to fix by pressing/turning some button? I’m kinda desperate, I want to be able to record as soon as possible.

    • http://www.homestudiocorner.com Joe Gilder

      Hi there. It could be the mixer. It could also be one of your cables.

      But yeah, I’d be hesitant to run thousands of dollars of mic/preamps into a cheap mixer.
      I love stuff from Presonus. I’d start there.


    • Kamp

      Like Joe said, check your cables. Make sure their not running parallel to any power cables (Cross at 90 degrees), including usb. Very, very small chance, but noise could enter the signal chain from the computer that way if your not using balanced cables. That’s what I would think if you don’t here the noise through monitoring. If you’re serious about this career path, invest in balanced cables wherever you can use them as you can afford to.

  • vpvpvpvp

    I have a Presonus Audiobox that I want to connect to a Rockman Ultralight. The Rockman is a pretty rare preamp and I haven’t recieved it yet in the mail, but if you could give me any help at all with connect the two together and into my macbook, I would appreciate it greatly. Thanks for posting this page!

    • http://www.homestudiocorner.com Joe Gilder

      Sorry, but I’m not familiar with that piece. But any advice I would give you is in the article on this page. You should have everything you need to figure it out.

  • Ben

    Hello Joe, I completely understand the best way to connect the pres to my studiolive. Thanks for your advices..

    Now i need your help/opinion. I’m in a “kind of” related project, I’m building a desktop panel to bring all the XLR and 1/4″ inputs from the back of the studiolive to the front, and i can’t stop thinking the following:

    – I know (it’s in the manual) when you connect a 1/4″ line, lets say “bass” into one channel (into the LINE input), the preamp on that channel is bypassed, and obviously the built in preamp doesn’t affect the signal. All clear here.
    – Now, I’m thinking to install a couple of “Combo XLR/Jack” female chasis connectors on my new front panel to save some space, but here is the thing: Does the pre “bypass” effect comes from the mechanical inserting of the 1/4″ line? or it activates/deactivates automatically depending on where is getting “signal” from?

    I would like to keep all the conections at the back of the mixer in place, not move them, and combine the XLR and 1/4″ inputs of each channel in one single Combo Jack per channel in the front panel (Obviously, combo xlr/jack have separate pins for each connector)
    Would this work?? Or is it going to keep “bypassing” the mic preamps because there are 1/4″ plugs always inserted on every channel??

    Great videos, info and blog. Excellent job!!
    Thanks a lot, from Chile.

    • http://www.homestudiocorner.com Joe Gilder

      Great question. First off the preamp isn’t completely bypassed. You can still adjust the gain up and down with the preamp knob. Just if you set it at unity it doesn’t add or take away volume.
      But I’m guessing you knew that.

      To answer your question it doesn’t matter what’s on the other end of the cable. All that matters is which input is being used on the back of the mixer, line vs mic.

      • Ben

        Hey! thanks for your answer.
        Well, if I get it right, then it will work to use the combo xlr/jack..
        It will be pretty cool to have them on the front panel, and plug a mic xlr or line in the same connector. Im thinking on make a 12 COMBOS multipar..

        Thanks again and, a thought.. Have you ever think on put all your posts together in one single “book” ?? I’m very happy trying to read every single post you have made, and it’s being very helpful to get better every day.


        • http://www.homestudiocorner.com Joe Gilder

          Y’know, I have thought about it before. Then I’ve thought I want to write a book from scratch. Then I get distracted by some shiny object.

  • matt

    I don’t fully understand, I have a mic plugged into my presonus studio channel and it into my mbox mini….am I wrong email me more of so. Squaredrecords125@gmail.com

    • http://www.homestudiocorner.com Joe Gilder

      Yup, that’s right!

  • Ej

    Phantom power 48v are required for condenser mic

  • Codi

    I have a M-track 2channel interface, with blue bluebird mic, everything seems to be setup properly but the vocals recorded seem to make everyone sound like a chipmunk, could this be cause i need a preamp? or is either the mic, daw, or interface deffective?

    • http://www.homestudiocorner.com Joe Gilder

      Hey Codi,

      It’s not a preamp issue. Something’s wrong with the interface or a software setting. Sounds like a tech support call is in order.

    • Crookid

      It’s a driver issue. This happens to me when I put a compressor on only one track in my DAW then try to record to a track without a compressor plugin.

      Try updating the drivers and/or calling support.

  • Cole

    Hello Joe! So I realize this is a super easy question. So a TR doesn’t have a plastic shielding covering the soder points and a TRS does have the shielding, right?

    • http://www.homestudiocorner.com Joe Gilder

      No it’s not really about shielding. a TRS has 3 conductors. A TS has two.

      • Kamp

        S=Shield (the longest metal part)



    • http://www.homestudiocorner.com Joe Gilder

      You don’t “need” one. But you certainly can use one to give you different sounds.

  • Faiz

    I want to know that can i connect two microphone in my audio interface ( for example focursite 2i2 or maudio 2 channel) and at the same time connect my guitar through line input ?

    • http://www.homestudiocorner.com Joe Gilder

      If it’s a 2-channel interface you can’t connect 3 inputs simultaneously.

  • Tommy

    I just bought a dbx 286s and I have a focusrite saffire6. The saffire 6 only has 2 inputs. Both being mic inputs. What do I do in that situation? Run a trs out from the pre to the xlr mic input in on the interface? Let me know please. Tomrao4@gmail.com

    • http://www.homestudiocorner.com Joe Gilder

      I don’t know that specific unit, but I’d be surprised if it doesn’t have line inputs somewhere…

  • Dayne Meyerink

    I am trying to connect a studiolive 32.4.2AI to my laptop with an RCA cable into StudioOne but studio one opens and says that there isn’t an interface.

    • http://www.homestudiocorner.com Joe Gilder

      You need to connect it via firewire, not RCA.

  • https://vimeo.com/107771503 Gilbert

    Hi – thanks for this helpful very useful advice. Is it possible to directly connect the output from a preamplifier (eg a TA 2021 type stereo amplifier) directly to the microphone input on a high end DSLR camera where I have the ability to set the digital and analogue gain levels? I appreciate your help. Thankyou.

    • http://www.homestudiocorner.com Joe Gilder

      I would think that’s possible with the right cables…but I would check with someone who knows cameras. I don’t.

  • Serkan

    Hi. Now I have an m-audio audiophile sound card on my computer. (It doesn’t have XLR inputs or outputs.) And I use my behringer xenyx2222 as a preamp. (2 Line outputs to the sound card’s input.) But I want to buy presonus studio channel to have a better sound. ( And I noticed that I don’t need a multichannel preamp after a four year experience at home:) When I have Presonus Studio Channel, how should I connect it to the computer. Should I connect it to the other preamp’s XLR channel or directly to the sound card’s main input. If directly to the sound card, which output should I use on Presonus?