How to Connect a Headphone Amplifier to an Audio Interface

We often hear from musicians and recording engineers who need to boost listening volume of their headphones. I recently tried a set of Sennheiser HD-650s using the headphone output of a Focusrite Scarlett 2i2 interface and completely agree. Volume on the interface can be turned to 100% without threatening my ears. A headphone amplifier is the answer.

Alas, mating pro audio gear with typical headphone amplifiers is less than straightforward. Audio interfaces are built to accept balanced inputs and outputs. Headphones and most headphone amplifiers are designed for unbalanced connections.

What are Balanced and Unbalanced Connections?

Unbalanced audio consists of a signal conductor and a ground conductor. Thus, an unbalanced stereo audio signal requires only three wires: +L, +R, and ground.

Balanced audio contains an extra inverting signal for each channel. Balanced, stereo audio requires at least five wires (excluding shielding): +L, -L, +R, -R, and ground.

The equal and opposite signals in a balanced connection are subtracted at the receiving end, so that the signal level doubles and any symmetrical noise cancels out. Noise cancellation is why balanced output is standard in pro audio. Long cable runs and a plethora of devices need all the help they can get to keep a mix noise free.

Connecting Headphones to a Balanced Interface

You have a few options to drive headphones from your interface. Diehard audiophiles will hold strong opinions as to which method is best. In no specific order, you can:

  • Make peace with your interface’s headphone output – It may not be loud, but it is free.
  • Double amp to an unbalanced amplifier – Connect a stereo patch cable from your interface’s headphone output to the input of an ordinary headphone amp. This will boost listening volume, but is generally frowned upon by the HiFi community.
  • Connect balanced line-outputs to a balanced amp – Depending on the model, a balanced headphone amplifier may require a balanced headphone cable as well. JDS Labs currently produces no such design.
  • Connect balanced line-outputs to an unbalanced amp – The majority of interface owners we hear from wish to use the balanced line-outputs of their interface with a popular headphone amp, such as Objective2. To do so, you will need two TRS to RCA adapters (one per channel). Remember, balanced wiring differs from unbalanced wiring, so pay careful attention to the drawing below! Notice that only the positive (+) portion of the adapter is accessed, and we do not connect the inverting (-) signal. After connecting the TRS adapters to your interface’s Left and Right TRS outputs jacks, simply connect an RCA cable between the adapters and the RCA inputs of your amplifier as shown:

 

 

Selecting Maximum Gain

To achieve more volume than your interface’s own headphone output, it’s important to customize your new headphone amp with optimal gain. You will need to refer to your interface’s specifications. Assuming you use its balanced outputs with Objective2, use the following equation:

Maximum Gain = 14/(VRMS of Balanced Output)

For example, Focusrite’s Scarlet 2i2 is listed with a Maximum Line-Output of +10dBu, which converts to 2.45VRMS. Your new Objective2 should be configured with high gain of 14/2.45 = 5.6x. Low gain can be left at 1.0x. Since a configuration of 1.0/5.6x is unlisted at jdslabs.com, please mention your special request in the Order Notes field during checkout.

Feel free to reply below or reach out if you need more help!

48 thoughts to “How to Connect a Headphone Amplifier to an Audio Interface”

    1. I use cables similar to this, which I think it’s better:
      https://www.amazon.com/Hosa-CPR-201-Stereo-Interconnect-Cable/dp/B000068O16/ref=pd_sim_267_2?_encoding=UTF8&pd_rd_i=B000068O16&pd_rd_r=3B510QNBCMKZ14ET2PPF&pd_rd_w=LXfBw&pd_rd_wg=hO3qc&psc=1&refRID=3B510QNBCMKZ14ET2PPF

      However, I think there can be a THD+N penalty with the 2i2 when using unbalanced connectors. An active balanced to unbalanced solution might be better. However, most off the shelf ones are worse than the cable solution. There are some ebay bare board solutions though.

      1. That is true, and we have an active balanced-to-unbalanced design in the works. @Jude will be seeking beta testers ASAP.

        1. What does the THD+N penalty mean in the case of connecting the amp (unbalanced) to an balanced output on the audio interface? Will I experience more noise? Losing clarity?

  1. Hi, thanks for the article it’s teally helpful.

    I’m a little confused however on whether to buy the leads as suggested in the article or whether to pick up the kind as suggested by ‘ULTRABIKE’ above?

    I’m not technically minded enough to understand the talk re the ‘penalty’ he referred to.

    Thank you

  2. Hey, thank you for this amazing article but my knowledge in this area is limited.

    I have the Topping Dx3pro amp/dac for my Sennheiser HD 58X and Behringer UMC22 audio interface to record from Audio-Technica AT2035. Can i connect the amp/dac with the audio interface ? If so, is there any advantages of doing that ?

    Thanks !

    1. If I am understanding your question correctly, no, there is no ideal way to use your amp/DAC and interface simultaneously as an *output* device driving headphones. You must pick one or the other. An interface is an amp/DAC with ADC. You can rely on an interface for input, and a separate amp/DAC for output, if you wish.

  3. Hi there,

    This was very informative! I have a 2i2 that I currently use to drive my studio monitors through the line outputs on the back of the interface. How would I connect a headphone amp to my interface while still using my monitors?

    1. @Andrew – While it may be considered ‘double amping’, you can use the interface’s line outputs for your monitors and rely on the interface’s headphone output to drive your external headphone amp. This works well for interfaces with good noise performance.

  4. I am not very technically inclined when it comes to this and I am just getting started so pardon my ignorance. I have a scarlet 2i2 interface and ah400 behringer. I wanted to be able to use multiple headphones but the output from my interface isn’t putting out a proper signal as I can only hear the left side on the headphone. It was also my understanding that the signal should be much cleaner but i am hearing quite a bit of distortion. Any suggestions please?

    1. Raza – Hearing only Left channel output suggests wrong cabling or connectivity between your interface and amp. If the above article does not bring you clarity, you may reach out to Focusrite. It’s probably easiest to run a TRS 1/4″ cable between the interface’s headphone output to the input of your amp. Using an incorrect TS cable may create the problem you’ve described.

  5. Can i connect my soundblaster x7 and focusrite 2i2 3rd gen like this way? Im not happy about the headphone output of the focusrite 2i2

  6. i connected my soundblaster x7 with my focusrite scarlett 2i2 ,like in the picture above. But im facing an issue and im not good in those kind of things so i dont know how to fix it. so maybe someone in here as the solution for me. But when ive connected my headphones and my XLR mic into the scarlett everything is working fine, when im switching over my headphones to the soundblaster my mic shows levels but im not able to hear the quality of it anymore myself. ive checked the in and outputs on my pc and those were correct.

    1. @Mart – Not sure I follow. Can you share pictures of the connections? The Scarlett 2i2 is a source, as is your Soundblaster X7, so I’m not sure what connection you are attempting to make.

  7. Really good post.
    Im sure this is the 3rd Gen Focusrite Interface because it has Balanced Line Outputs.
    I have the 2nd Gen Version with RCA Line Outputs. Can i connect the Headphone Amp just with normal RCA Cable to my Focusrite 2nd Gen or what is the best solution for me?

      1. My Problem now is, there are 2 different RCA Cables. Digital RCA Cables and Analog RCA Cables. Which one How can i know which one i need for my Setup?

        1. Any RCA cable can be used for analog input. “Digital RCA” implies a coaxial S/PDIF connection with a specific impedance. These are individual cables, usually indicated by an orange connector.

          Analog RCA cables are sold in pairs, with white and red connectors.

          1. Ok, ty so much.
            I have a last question.. The “Line Out” from the Scarlett has 430Ω. Compared to the Headphone Output <1Ω , it is rlly high.
            Is this a problem?

      2. In the JDS Atom page says: ” Unplug your headphones and Atom Amp’s knob adjusts volume of its RCA preamp outputs, so that you can control volume of your powered speakers.”

        Can I connect my 2i2 the way you did and then connect my active monitors (yamaha hs5) to the rca outputs of the Atom via RCA/Jack 6.35 (or XLR, you have to tell me which is better). I’m not talking about listening on the headphones and monitors at the same time, I’m just asking if is possible (and secure) to have connected both to the Atom and when unplugged the headphones off the Atom, can I hear music on the monitors.

        Thank you.

  8. First of all thank you for this.. Funny enough we both have the same brand of interface and I just got my 650s and was wondering how to achieve this. Question tho and forgive me for my lack of knowledge…

    Do you LOSE any sort of quality by doing it this way? I have a monoprice headphone amp and I’m able to switch between AUX IN and Usb DAC. As I’m switching back and forth between these 2 I’m noticing volume changes and I’m wondering If USB DAC is the better one since its Digital to Analog conversion…

    1. There should be no loss of quality using an external amp with your interface.

      As for your “AUX” device vs USB DAC, it’s difficult to know which is better. There are poor USB DACs out there, and excellent 3.5mm (aux) sources, and vice versa. Use what works best for you!

      1. Thank you for the fast reply!!!

        To be specific, this is my amp – https://www.monoprice.com/product?p_id=11567

        I hope this amp isnt poor!! It is only about $130 (canadian dollar) but I thought it did the job with my sennheiser 650. I just get a lil finicky when it comes to quality. Because while I’m on Cubase, I would want to use my Focusrite ASIO driver. Only way to do this is the current method that I have now..

        Focusrite – Line Out (Unbalanced) > Headphone Amp AUX IN > Sennheiser 650 headphone

        I ask about the USB DAC because when I switch it to that mode, I CAN’T use the Focusrite ASIO driver while I’m IN Cubase. Rather I’m forced to switch to the generic ASIO driver which doesnt run as smooth.

        Anyway I hope there are actually no loss of quality… it is hard to differentiate. I appreciate your reply and the blog.

  9. Hi John, excellent guide thanks!
    Quick question, if one were inclined to run a condenser mic through a 2i2 into an Xbox (or any other console) for voice chat, would running the unbalanced RCA jacks into a dual female RCA to 3.5mm TRS splitter work? Basically, the mic input can only be a mini jack.
    Thanks

    1. @Lukas That is an RCA cable (no TRS connection?).

      THD+N will depend on the specific interface; there is no way to give an exact answer without conducting measurements.

      1. @John that’s right, no TRS connection, however I was thinking plugging these onto a TRS -> RCA male (instead of female as in your initial post). This because it is very very hard to find the ones you suggested here in The Netherlands.

        About the THD+N: an exact answer is not necessary, to know some possible risks/effects will do, for now it doesn’t mean anything to me and I can’t make any sense of the technical information I find on the web.

  10. Great article! Helped me a ton recently when I was purchasing an amp to go with my interface to properly power my HD600’s. Just curious — what should the gain staging look like? Should I just simply max the monitor level on the interface and then adjust the amp gain to taste? Does any changes in gain staging make much of a difference? Thanks!

      1. I bought an O2 amp off of ebay with a high gain of 3.3x. What exactly does that mean and would that have any negatives for sound other than max volume? Ps: thank you for this article it has been a lifesaver so far…

          1. Awesome! Also what was that about thd+n penalty with this setup? Will it be a lot or not even an audible difference and how would this most likely manifest itself (distortion, noise ect.. ). I was considering a modi 3 but it’s technical specs don’t look all that much better than the scarlett’s dac. I was wondering if the balanced to unbalance cabling thd + n penalty would be enough to make the purchase worth it. Btw it’s so cool that you’re still replying to this thread you’ve probably helped a ton of people.

          2. Ok so just clarify there should be no loss in quality…
            I’m so sorry but I’m pretty OCD.

  11. What if I want to output to both a headphone amp and my studio monitors, but remain balanced for the monitor connections? I guess the headphone output is probably the way to go, unless I get some sort of mixer. I wonder if there’s a studio subwoofer with those kinds of extra outputs, that I could output to a headphone amp from it. I might try that route if nothing else presents itself.

    What I really would like to see is a small, simple device with a set of L/R balanced inputs, L/R balanced outputs, and L/R RCA outputs. Then I could just leave my interface with TRS to the device, out of the device to my monitors, and out of the device to my tube headphone amp.

    Does something like this exist?

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