Household & Living

Review: Asus Xonar Essence STU headphone amplifier

Review: Asus Xonar Essence STU is a great slim device but small size cause some drawbacks like lack of high-end audio equipment
Review: Asus Xonar Essence STU

Review: Asus Xonar Essence STU – After quite a few years of CDs, music seems to have deteriorated a bit, at least in quality. If you’ve bought a lot of CDs, you’ve probably heard how good they sound, and MP3 can be a bit of a disappointment as a result. Of course, MP3s usually give us good access to huge amounts of music, and that’s their value.

But the tide is changing. At this point, we are just starting to see lossless music and even “studio master” quality tracks being sold online. If you happen to like high-quality audio, this will likely appeal to you – and you need a way to listen to this music. Your computer may be playing high bit rate audio, but your hi-fi system may not.

Whatever you need, the Asus Xonar Essence STU is designed to deliver truly great quality music. How does it hold up?

What is Asus Xonar Essence STU?

For computer users who want a much improved sound quality, including support for higher bit rates that give a better sound than CD quality, the Asus Xonar Essence STU offers its services as a sound card for laptop or desktop. It is happy to accept 24bit / 192KHz inputs from USB sources.

Review: Asus Xonar Essence STU

Connect your PC or Mac via USB and it will show up as an audio device. From there you can use it like you would any other sound card. Your PC can send music to it, but you can also connect inputs from other devices that use digital RCA or optical connections, or even a smartphone or tablet that you can simply use via the 3.5 mm jack input.

You can then choose to listen through headphones – this is ideal if you have a decent pair – or pass the sound through to an amplifier to listen through speakers. No amplification is built into the Asus, which significantly increases the cost of installing it in a system.

In audiophile circles, the digital to analog converter (DAC) is a long-cherished tradition. When the CD came out, the purists – as soon as they said they preferred vinyl – bought their CD ‘transport’ separately from the DAC. This meant that your hi-fi became a lot of speakers. The CD transport would be connected to the DAC via a digital cable, which would decode the digits and relay them to the amplifier via analog RCA jacks or the like. Most of us only used microsystems and were done with them.

The truth is, the best solution lies somewhere between how most people did things and how high-end users did it. However, decoding from digital to analog has to be done properly, and that’s what the Asus wants to do.

To run the Xonar Essence STU on a PC, you need to install a simple driver, which takes a few minutes. You can get this from the Asus website, but without it you won’t be able to run the device as a sound card, although you could send music to it via digital connection.

Design of Asus Xonar Essence STU

The Xonar Essence STU is very small. Just big enough to have a few volume controls on the front panel – one for headphone output, another for output to your amp. There is a small power button and an input selector. There are also some status lights to let you know which input you are using.

Apart from the volume control, everything is small. Neither button is particularly difficult to press, though, and there’s a tiny click from inside the machine that signals it to turn on. There’s a headphone jack that also uses the larger 3/4-in jack, so whichever pair of headphones you want to use with it isn’t a problem.


One problem we noticed after using the Xonar Essence for some time was a weak glitch that would repeat during a cycle. It was a kind of static sound, but one that repeated itself on a regular basis. We had our test sample replaced with a new unit and the problem went away for a while. When we put a DECT home phone near the Xonar, the whole thing erupted with noise.

So, what can we conclude? Things that transmit radio waves are bad. In your home, there are things like home plugs, microwaves, Wi-Fi routers and so on that are all causing interference. But it is also an inevitable part of modern life. If you could see radio waves, you would see that the world is full of them. So we’re a little disappointed that the Xonar was not better able to handle this particular malfunction.

Once we removed this sound source, the Xonar became brilliant again, with no sound issues.

Sound quality

Regardless of the interference issues, we quickly fell in love with the sound quality of the Xonar Essence STU. We used all of our best headphones, from high-end Denons to Calvin Harris tuned Sol Republic studio tins and some Focal Classics. The results are indeed very gratifying. The quality of the sound produced here cannot be disputed, and you would have to spend a lot of money to get it on a hi-fi component.

You hear the cleanest possible sound through headphones. Only the way your headphones are designed and tuned changes the sound you hear.

Output to an amplifier is much more complicated. We used two different amplifiers during our test. The first was a very flat sounding system that again didn’t add a tone of its own and left the sound as it was recorded. The second thing we had was a system that was less audiophile-oriented, and it gave us a little more control over the output.

We like this neutral approach because the Asus gives the best possible quality that you can then tune to your ear with the rest of your equipment. Interestingly, you also get dual volume controls so you can adjust the output level through the rear mounted RCA jacks, as well as the headphones.

Usually we prefer the RCA output to be just a “line” level, with no option to increase or decrease, but you get this extra control here. It may be helpful for some who wish to increase or decrease levels to match their other equipment. The only problem is that the watch faces are the same so you can sometimes get confused and adjust the wrong thing.

Review: Asus Xonar Essence STU

On the back you can also flip a switch that allows you to amplify the output to your headphones. This is very useful if you have cans that require a lot of force to drive them, as is sometimes the case with larger home headphones. It’s a nice feature, but be careful not to use it with smaller headphones.


The sound issues on the Xonar Essence bothered us initially, but once we figured out the source of interference, everything was fine. Do we expect this on audio equipment? No not really. The problem is, Asus has gone for a small device, which is great, but with that, you lose some of the shielding that makes high-end audio equipment much less prone to such things. There’s also no way to ground the device, so if mains hum was an issue – it shouldn’t be as it has DC power through a transformer – you’d be stuck with that too. But when it comes down to it, wireless things can interfere with a lot of other things, so keeping them away from the Asus is a must.

When you do, the sound quality of the Xonar Essence is fantastic. We’ve heard a kit that costs a lot more and doesn’t really sound any better. What you get on your headphones is clear and wonderfully flat sound. We paired it with three of our favorite headphones and they all sounded great. From our clean monitors to our more bass-weighted everyday looks.

For computer users – and that’s what this product is really about – this is a great way to get great quality audio. There are now some music streaming services that offer music that makes buying good audio hardware like this Asus worthwhile. And most importantly, if you pair the Asus with a high-quality amplifier and speakers, you get fantastic sound.

It’s not without its issues, but overall we enjoyed using the Asus Xonar Essence STU. It has become an important part of our home audio system, which largely revolves around the PC.

In favor of buying Asus Xonar Essence STU

  • Great sound
  • Compact design
  • User friendly
  • Reasonable number of entrances
  • An ideal solution for laptops or desktop computers with terrible built-in audio

Against buying of Asus Xonar Essence STU

  • External interference can affect sound quality
  • Quite expensive