Asus Xonar Essence STU – Review

I’ve heard only good things about the headphone related products from Asus, especially the  Xonar Essence One and its Muses Edition. So, in that direction, I hope that I will get to review them soon.

Meanwhile, I’ve got my hands on the little brother of the line-up, the Xonar Essence STU.

More than 5 years ago I had the Xonar Essence ST sound card and this is the external usb version of it. I am quite curious on it’s performances, so let’s get a closer look.

Looks, Build Quality and Specs

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The STU is quite small. I can easily insert it in my laptop bag and take it to work for example. The case almost fooled me at first, as I thought it was metal, but it is a very hard plastic. The overall build quality is quite ok, but it would have been better if the case was metal, as with plastic, it can pick up some interferences on the way.

Let’s take a closer look at the specs.

Asynchronous audio transfer

Asynchronous USB transfer mode separates unstable and noisy clocks generated by the computer or its USB interface logic, maintaining sync with master clock circuitry on Xonar Essence STU.

This should be an important step up from the internal sound cards like Essence ST and STX, as this should isolate it much better from the noisy pc environment.

Digital-to-analog converter (DAC)

High fidelity Texas Instruments PCM1792A DAC delivers accurate digital-to-analog conversion, sensational audio clarity, and low distortion.

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In the above picture you can also see the swappable op-amps : NS-LME49720 and NS-LM4562NA.

Audiophile-approved capacitors

WIMA FKP2 and Nichicon Finegold capacitors deliver balanced and rich sound.

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The headphone amplifier is based on TPA6120A2 and it supports up to 600 ohm impedance.

It has the C-Media CM6631A High-Definition Sound Processor .

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It supports up to 24 bit and 192 khz and it has an impressive 120 dB Signal to Noise Ratio (A-Weighted) on the front  out and  >0.00036 %(-108 dB) Output THD+N at 1kHz .

One thing to remember is that the headphone output has 10 ohms impedance, so it wouldn’t be the best choice for IEMS or low impedance headphones.

The Essence STU has 2 rca outputs and Aux, toslink, coaxial spdif, usb inputs.

You can also set it on low/high gain depending on your headphone needs.

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Tests and Listening Impressions

The tests have been done with Decware Taboo MK3Audeze LCD-X with Toxic Silver WidowBurson ConductorAudiobyte Hydra-X, Sennheiser HD800 and AG500 Power Regenerator, Focal Spirit Classic.

The usb implementation from the STU is quite good, but adding Hydra-X on the SPDIF input improved the sound in a lot of ways, making it more detailed, natural, spacious, with better transients, better layering, imaging,  etc

While it drives Audeze LCD-X in a decent way, the the 10 ohms impedance was felt a little bit, as it  took a little from the clarity and transparency of the sound. HD800, on the other hand was a very good match for it.

Another thing I liked about it was that the drivers were easy to install and stable, as I didn’t stumble upon any errors or bugs while testing it. The drivers have ASIO support and worked from first shot with foobar2000. The STU has a led on the front panel that shows you if the stream is bitperfect.

Pink Floyd – Money

I have been pleasantly surprised by the details the STU was capable of. The bass had a good punch, even on HD800. The guitar had  good texture and was well extended. When the passage got crowded, I think the STU handled it very well showing good layering and PRAT.

Paco De Lucia – Al Di Meola – Passion, Grace And Fire

The STU managed to surprise me again with a good performance on this song too. The soundstage was spacious and the guitar was very nicely reproduced with good details, texture and a holographic feel that showed  the size of the room.

Bon Jovi – Hey God

When the song starts, the sound of the match burning is very detailed and very well reproduced by the STU. Throughout the song it presented itself with a very good PRAT, showing a lot of energy that makes you head bang. Also the bass  has a very good and pleasant punch. Bon Jovi’s voice has good, natural texture, especially with Hydra-X attached to it, and is very fine layered between the well textured and heavy guitars.

Coldplay – Speed of Sound

I also found that the voice had a very natural and pleasant tonality attached to it.  The drums had a very good impact and were very punchy throughout the song, creating an energetic and catchy vibe.

Carol Kidd – My Funny Valentine

Carol’s voice is playing with a with grace between the sparkly guitar. Again a very good example where STU manages to bring a very good song presentation.

Infected Mushroom – Project 100

The song begins very strong with exploding energy and a very engaging and punchy bass. The drums and the heavy guitars are very impressive and made  me love the STU.

Vivaldi – Concerto No. 3 in F major, “L’Autunno” (Autumn), RV 293. 3. Allegro. La Caccia

I’m listening to the Chesky version of the song. I must say that Essence STU did not disappoint here either. On the contrary, it made quite a good impression. The soundstage was  spacious and had good positioning. The instrument separation was quite decent and with hydra attached it got very good.

The instruments were very well layered and presented a lot of details.

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I found the bass to have a very good punch and depth, making the drums, heavy rock guitars, cellos very enjoyable.


The mids are quite good making the instruments and voices very noticeable. Actually the voices had a very good, natural tonality and a decently detailed texture.


After my experience with the Essence ST sound card, I expected harshness from Essence STU. I was pleasantly surprise to see that this wasn’t the case, as the treble is well extended without being bright, not even on HD800.

Soundstage, layering and instrument separation

While it’s not the best soundstage i’ve ever heard, considering the price range, the STU behaves very well here showing a spacious and well layered scene. I’ve enjoyed classical music and other music types that need these qualities very much with it.


On some songs, the STU becomes very energetic and sometimes can make you headbang or dance along.

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Asus Xonar Essence ST was my first good soundcard / dac when I started with this passion. It was a big step up from my older soundcard, but I felt that it was a little unnatural and harsh sometimes. Considering the STU should be an external version of it, I expected similar sound.

Well, it was a good surprise, as the sound wasn’t bright at all and had quite a pleasant & natural tonality.  The isolation from the noisy computer environment was felt quite easily. Combined with the async usb, the jitter must be a lot smaller than on ST/STX leading to better transparency, less harshness and more naturalness.

Adding Audiobyte Hydra-X on SPDIF improve things a lot in the direction mentioned above.

Another thing that was impressive about the Essence STU, is the fact that it drove the Sennheiser HD800, even in the bass department and was overall a very good match for it.

Considering what it is offering and at what  price, I find it very easy to recommend it. Actually, this is the best option i’ve stumbled upon until now at this price.


  • good punchy bass with good depth
  • good layering and instrument separation
  • spacious soundstage
  • good prat & energy
  • well extended treble
  • natural and pleasant voices
  • quality components
  • a lot of inputs
  • gain selector
  • good price
  • sturdy build quality


  • the input selector is quite slow
  • the case made of plastic and could be influenced by external interferences

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