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Asus Xonar STU DAC and Headphone Amp Review

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by Ed Selley
Home AV Review

5

Asus Xonar STU DAC and Headphone Amp Review
SRP: £270.00

Convention dictates that the hi-fi market is in decline and this - in a numbers game at least - is true. Behind this rather depressing factoid are some interesting other elements to consider though. The first is that exactly what constitutes a piece of Hi-Fi equipment in 2013 is open to debate. The laptop I’m typing this on would never be classified as audio equipment but as well as acting as a work platform, it can also effortlessly stream a bewildering variety of audio files to suitable hi-fi equipment. Likewise, the boom in headphone sales has seen a ‘hi-fi’ category expand enormously mainly to exploit something that isn’t.

With the margins becoming distinctly blurry, the appeal for certain companies about the hi-fi category is that while it might notionally not be growing, compared to some other parts of consumer electronics, it looks like an oasis of calm. The sales figures for desktop computers are not so much in decline as they are in freefall of late and the figures for laptops look less rosy too as tablets continue to eat away at the roles and responsibilities we once assumed were the sole preserve of conventional computers. This being the case, if you are a computer manufacturer, all of a sudden, hi-fi doesn’t look so bad.

Asus is a case in point. As a company invested in computer construction, they have taken the logical decision to take their soundcards and turn them into standalone DAC’s. We have already seen the Xonar Essence One which while not a perfect performer, showed some commendable abilities when used as a headphone amp for digital sources. This has now been joined by the Xonar STU which is another DAC and headphone amp and intended to fit in below the Essence One. This is a category where conventional hi-fi companies have plenty of offerings - can the Asus take the fight to them?

Design

The STU is a USB headphone DAC in a similar vein to the Essence One which means that it isn’t completely normal in design. Like the larger model, the STU has separate volume controls for the analogue output and the headphone output which represents an unusual degree of complexity at the price - most of the competition effectively shares a circuit for the two functions. This means that the headphone socket is impressively beefy - Asus claim it has the gain and current handling to do justice to 600 ohm headphones. Given these generally cost a fair bit more than the STU does, it is an impressive achievement.

Asus Xonar STU

The STU is also fitted with a feature that wasn’t present on the bigger Essence One. The main volume control that affects the audio output can be switched out of the circuit so that the STU runs as a line level device. Actually making the change though means taking the lid off and fiddling with the innards rather than the less involved process for the Cambridge Audio DacMagic Plus or Audiolab M-Dac- although both of these models are more expensive than the Asus. This is still useful to have though if you are connecting the STU to something with its own volume control.

Internally, the Asus is built around a Texas Instruments/Burr Brown PCM9211 chipset and a C-Media USB interface. The volume control and variable output means that the internals of the STU are more complex than some rivals like the Micromega MyDac which can generate an output from the DAC chip alone. The STU is fitted with what seems to be becoming an industry standard for affordable DACs, one optical, one coaxial and one USB input. The USB is similar to the one fitted to the Essence One in that it is an asynchronous design with a dedicated driver that supports ASIO playback with suitable software. What is absent on this less expensive model is the separate upsampling circuit and any upsampling takes place in the DAC chip. The specifications do state that both 44.1 and 48 kHz multiples are supported though.

Asus Xonar STU

The aesthetics of the STU are slightly confusing. When I first saw a picture, I assumed absent mindedly that it was of a similar sort of size to the Essence One. The styling looks vaguely reminiscent of 70’s Japanese brand gear with separate chassis and glossy front plate. The packaging and the unit itself were a bit of a surprise when I took delivery of them. The STU is actually very small indeed. It stands no more than five centimetres tall and it is roughly the size of a hardback book. This means that the controls are rather smaller than you might think. I rather liked the styling of the larger Essence One - it looked different to most of the competition and the curved top plate is visually a bit different. I’m less convinced by the STU - it doesn’t quite pull off retro look because it is so small and the result is going to look a bit odd in the context of a system.

The overall construction of the STU is satisfactory but not great. It is interesting to compare the overall feel of the Asus with the Micromega. Both are light, small and predominantly made from plastic but while the Micromega feels like this was what they set out to do from the outset and is quite a cool thing as a result, the STU feels like Asus wanted to make it out of metal and other exciting things but couldn’t due to the price. As such, the STU doesn’t feel completely convincing. The quality of the buttons and controls is not hugely substantial although in fairness, neither do they feel like they will come away from the unit. The power supply is external and the Asus has a block PSU into which a figure 8 mains lead connects. This means that you get a long cord but the arrangement is bulkier than either a wall wart or internal PSU.

Asus Xonar STU

The USB input needs a driver to function - it wouldn’t work on the default driver on either machine I tried to connect it to. The good news is that the Asus driver installed in a logical and straightforward fashion and worked flawlessly after I did so. It also had no adverse effect on other USB devices I connected after installation.

Setup

The Asus was connected to my Lenovo T530 and my wife’s Packard Bell unit - both Windows 7 machines. This allowed for audio software such as Songbird, Spotify and Foobar to be used as well as music competition software including Ableton and Kontact. Partnering electronics included, the Naim UnitiQute 2, a Cambridge Audio 851A integrated amp and Neat Iota and Audio Note AN-K loudspeakers. The headphone amp was tested with the PSB M4U1, Sennheiser PX360 and Final Audio Design Heaven IV. The conventional digital inputs were tested with a Cambridge Audio Stream Magic 6.

Sound Quality

With the USB driver installed and connection made successfully, the Asus revealed some distinctive performance traits from the outset. There are some aspects of performance in common with the larger Xonar and in some ways these are amplified by the STU. The Asus is a powerful and frequently exciting performer. The potent and sparse recording that is Boards of Canada’s Tomorrow’s Harvest has well extended and powerful bass and an impressive sense of air and space to it. The treble that the Asus has is well lit but avoids becoming actively bright or harsh- provided that the recording is good.

Asus Xonar STU

The initial listening I did with the Asus comprised music that was largely well recorded - this was more by accident than design. When I switched to Love’s 1967 masterpiece Forever Changes, the Asus was rather less happy. The recording is not a bad one - it has plenty of dynamic range and care was taken in the original mastering - but there is a thinness to some parts of the frequency spectrum that can sound a little strident (this is one of the reasons why the vinyl copy is so sought after as it doesn’t suffer anything like as badly). The Asus unfortunately locked on to this thinness and at various stages sounded positively screechy with certain instruments. Investigating this further with other less than perfect recordings revealed that the STU is able to do some wonderful things with well mastered material but is merciless with less brilliant ones.

The interesting part of this is that like its bigger brother, the STU is less concerned about the actual resolution of the file being played as the original level of effort that went into mastering it. Well sorted albums sounded fine on Spotify while a poorly sorted piece of high res - Nirvana’s Nevermind for example - just sounded thin and angry. In partial defence of the Asus, this recording is thin and angry but while the Micromega could point this out while still keeping the basic passion and intensity of the recording in focus, the Asus just strips it bare.

Asus Xonar STU

The partial upside of this is that from a semi pro perspective the Asus is potentially useful. If you are working with digital files and the end results sounds good on the STU, the chances are you have done a good job on it and that it is likely to sound good full stop. My wife felt that this was potentially useful in her studio work but as a result, it is a bit of a stretch to describe the Asus as ‘fun.’ Switching to the other digital inputs suggested that this particular performance trait is present across the digital board as a whole so bypassing the USB connection (which bypasses quite a bit of the total functionality of the DAC) won’t alleviate it.

The biggest strength of the larger Essence One was the headphone amp which was hugely powerful, extremely transparent and generally fun to listen to. The STU manages to retain some of these admirable traits. For under £300, this is a powerful and well implemented headphone amp with a low noise floor and the ability to drive some tricky pairs of headphones to high levels without breaking sweat. The only problem is that the same merciless and slightly steely performance remains over headphones as it does over the analogue outputs. Given that some pairs of headphones are more revealing than similarly priced speakers, this can be a bit of a recipe for disaster although using the STU with the PSB M4U1 created a combo that was still fairly revealing without being quite so aggressive.

Asus Xonar STU

Using the preamp of the STU into a fixed input on the 851A didn’t change too much either but did at least show that the volume ramp is linear and free of imbalances or other nastiness. The rather small size of the volume knob meant it wasn’t the most satisfying device to use as a preamp as very fine volume adjustment was a little fiddly and hard to sort. As a desktop stereo system with active speakers, it would work reasonably well and the gain involved should be ideal for the task but as with other aspects of the STU, you would need to choose your active speakers with some care. Anything as merciless as the Asus is likely to result in a system that is going to shred quite a bit of music.

Verdict

6
AVForumsSCORE
OUT OF
10

The Good

  • Potent headphone amp will drive most designs
  • Well implemented USB driver
  • Can sound good with well recorded material

The Bad

  • Can be strident and thin with less than perfect recordings
  • Slightly lightweight build
  • Odd appearance

Asus Xonar STU DAC and Headphone Amp Review

The Asus Xonar STU is something of an oddity. The styling suggests it might be a lifestyle orientated product but the performance isn’t really in keeping with this. When you play high quality material through it, this is a very capable DAC that can sound genuinely engaging. The problems arise when you play music that isn’t as well produced. It isn’t right to say that the Asus is ‘too revealing’ - the Micromega MyDac is the same price, capable of similarly excellent results with good recordings without being anything like as tough on poor ones. When it comes to the Xonar STU, it simply seems that less high quality recordings provoke some bad habits in the Asus that are present all the time. It has a good headphone amplifier for the asking price but for the price of a good night out, you can have the Essence One which is better still, more forgiving sonically, comes with more pleasant controls and offers better connectivity into the bargain. The Xonar STU is not quite one thing or the other and as such it is not something I can unconditionally recommend.

Scores

Build Quality

.
.
.
.
6

Connectivity

.
.
.
7

Ease of Use

.
.
.
7

Features

.
.
.
7

Audio Performance

.
.
.
.
6

Value for Money

.
.
.
.
6

Verdict

.
.
.
.
6
6
AVForumsSCORE
OUT OF
10

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