Review Work (Headphone Amplifier)

Stoner Acoustics UDXA – Done it again

DSCF8657I really like Stoner Acoustics’ products and they definitely have made their name throughout the audiophiles community especially with their excellent DAC that blend good price with good performance, I thoroughly enjoy their products and to be honest, these two years of my inactivity in review job I actually use their products during my personal music listening session, not that I don’t have another higher price DAC or amplifier lying around but I just like their products and the sound of their products are truly excellent, I can’t stop the amber in my heart when I realize they have released their latest DAC/Headphone amplifier, the UDXA (that obviously, I am reviewing today)

They have released two latest product, the UDX (Pure DAC) and UDXA (basically the UDX with built in headphone amplifier)


DSCF8661Stoner Acoustics UDXA (450 USD)

This device is definitely not a portable DAC/Headphone amplifier but it is very transportable, not really heavy and I don’t mind to bring it to travel if I would like to have some serious listening in the hotel (but who will), one thing that make me prefer the UDXA than the EGA (Stoner Acoustics previous flagship full balanced headphone amplifier) is that instead of only a full balanced DAC and headphone amplifier output, UDXA is capable of provide single ended output for both the DAC and headphone amplifier, this is really a nice touch since buyers able to have choices in hand instead of limited to just balanced output, this is the reason why I don’t really use the EGA after reviewing it because not every headphone able to modify to balanced easily, and thanks God Stoner Acoustics finally able to correct this and make UDXA a more flexible DAC/Headphone amplifier in a box.

Speaking of input, UDXA is still quite limited and it is not difficult to see that Stoner Acoustics are focus more on computer and smartphone audio users, it is just offering USB input which worked fine for both the computer and Android phone, no problem here. However, it is important and crucial that if we can add an optical input as this will make the DAC/Amp much more flexible, for example I can’t use the Chromecast Audio to connect to the system with just the USB input, not a big issue and I believe majority of the audiophiles here use just the USB input but for some and the ever developing headfi world, with more choice of the input will just give more option and future proof.

Stoner Acoustics are confident with their DAC part of the UDXA and I am glad that they provide a RCA jack/XLR (for full balanced audio) at rear panel to let user use UDXA purely as a DAC only and connected to another amplifier, in fact it has a XLR output too at the rear and this is such a rarity in this price range, if you would like to try full balanced system in the future, especially those with headphones that can easily modify to full balanced (those Sennheiser HD58x/HD600,650 6xx and Hifiman series immediately come into my mind), it is so much fun that you can experienced more with just one single device and I think Stoner Acoustics have just made the right move to offer both single ended and full balanced output, the best thing is, UDXA sounded excellent with both of the option.

However, I am not fully satisfied with some of the design of the UDXA, particularly the volume control there is no display for easily tell you what mode you are in now and your volume level. If you want to adjust the volume of UDXA you need to press the A or B button to either lowering or raise the volume of the UDXA, this is not the problem but UDXA provide 256 step of volume controlling and there is such a long press for you to adjust from minimum volume up to maximum volume although you can fine tune the volume, but for me the hardest part is that you don’t know your current volume level without a proper display, for example if you play some hard to drive headphone and at the next time you switch to an easy to drive IEM, the high volume will just blow your ears to deaf. I believe (but not yet asking Stoner Acoustics) that their choice of using such volume controller is because they want to maximize the sound quality of UDXA, previously Stoner Acoustics did tell me using the usual volume controller will degrade the sound, I am not much a technical guys and this is just my wild guess but as an end user, it is quite a pain to not able to see the volume level of the UDXA.

Operating the UDXA is quite simple, for PC users we need to download the dedicated drivers (which is the same driver for EGD) and install it, then you are good to go, DSD format is an easy task and UDXA can play them flawlessly, let alone those high bitrate audio files format, UDXA can play everything that I throw at it, UDXA is small enough that you can place them and not obstructive on your table, to be fair the finishing is not top notch like those big brand capable to offer you but the build quality is good enough and that should be no issue.


Sound Quality

I have tested the Stoner Acoustics UDXA mainly with Sennheiser X Massdrop HD6xx, Philips Fidelio X2 and ZMF V1, connected to a PC with Foobar2K (Lossless music files) and Spotify Premium. When I want to compare the amplifier section, I will connect it as line out to Teac HA501


As DAC/Amp : If sound quality is what you are pursuing then you will leave nothing to disappointment. The sound character is very ‘Hi-Fiish’, it is impressively balanced and neutral (tilt little to warm) with very nice soundscape/soundstage and imaging, all of these topped with clean and reasonably transparent sound. Honestly, I actually quite enjoy it, thoroughly, using it as a DAC/Amp in a box and found using an external amplifier a little unnecessarily and just caused hassles. When you have a built in headphone amplifier this good, why bother? It is really good.


When I played the ‘Joan Baez 75th Birthday Celebration’ live album (if you not yet listen to this album then you should), the sound reproduced with surprisingly realms and you definitely can tell that this is an album tailored with good recording technique, the soundstage is wide and at the same time is deep and you can immerse yourself in great imaging. Vocal of Joan Baez is Godsend and I really love it (Can’t believe Joan Baez still have her amazing voice even when she is in her 75th), UDXA played it with how it should be, no, it is not liquify nor thick nor excessively warm that added ‘taste’ to the vocal, no, it is just neutral (Slight warm) and balanced, play it like how it should be played, you just revel in the music.


The album ‘Communique’ by Dire Straits, guess everyone should be familiar with this album, the vocal of Mark Knopfler is amazing and the recording is equally nice too. UDXA put space for every instrument and music to breath, it is a clean presentation and I can see UDXA didn’t add up too much to the music reproduction, I see this as a good thing and it is very easy for you to pick your headphones, just pick the headphone that is to your taste and you should good to go.


You can select multiple type of filter when you press the ‘C’ button, honestly the differences among them are quite subtle, I mostly just use default filter, among them are:


Filter Type Display Colour Remark

Sharp Roll-off RED

Slow Roll-off BLUE

Short Delay Sharp Roll-off OFF* Default Filter Setting

Short Delay Slow Roll-off GREEN

Super Slow Roll-off PINK

Super Extra Slow Roll-off YELLOW

Low Dispersion Shot Delay CYAN


In my opinion, using it as a DAC/Amp combo is truly nice experience and using it in such way is very convenience, it is such a small device and have some really nice sound quality keep you wanting to listen to it more and more.


As DAC only (Connect to TEAC HA501) : I am quite satisfied when using UDXA as a combo, but when I start to hook up the DAC of UDXA to TEAC HA501, I immediately noticed the improvement of the external headphone amplifier bring to the equation, to be frank, HA501 (Listed at 999USD, selling for 532USD now at Amazon) is a headphone amplifier sell more than 450 USD price tag of the UDXA, so it will be relatively absurd if UDXA’s headphone amplifier section play better than the HA501 (a dedicated headphone amplifier), with HA501 as headphone amplifier and UDXA solely as DAC only, the music has much greater definition, more nuance and better define staging at it, it is no contest and the music/instrument simply have more space to breathe, a simple vocal track such as ‘Swing low sweet chariot’ and ‘let it be’ from Joan Baez’s ‘Diamonds and rusts in the bullring’ are able to revealed more and the definition squeezed out of it are simply amazing, but man, the HA501 carried listed price tag that double the UDXA (a DAC and a headphone amplifier in a box), so it is really no surprise here, however, for the price alone, if you are not making any A/B comparison, UDXA itself is good enough and taken the price into account, it is even more impressive, impressive enough that I will not hesitated to use it as DAC/Amp combo.


Equally impressive is UDXA is powerful enough to power up the HD6xx and Fidelio X2 to hazard volume level, with good control and good body, what I really like about it is the UDXA never sound thin and analytical in anyway, the musical factor is great and everything sounded so ‘Hi-Fiish’, which I really appreciated. The output impedance is low enough for me to play some earbud easily on it too, such as the Venture Electronic Monk Lite (40 Ohm) and some other earbud, versatile enough for your headphone collection.


Final Thought

Sometimes it is a little sad that seeing something that is very good but just can’t meet the sales figure to continue the company operation. I never questioned Stoner Acoustics’ sales achievement per month, but headed to the forum and you rarely see people discussing their products, are they product bad? No, not really, in fact they are quite good and certainly super good and always provide excellent price to performance ratio, it is just they are not that expertise in product marketing, however in term of product design that can give good sound, they are expert. I really hoping they can start to do some product that keep the good sound formulae but give a better fun, for example an DAC/Amp similar to UD125 but improve the sound and provide a bass boost option, a mobile friendly DAC/Amp such as the Apple Lightning audio adapter that are reasonable cheap and give better sound to the onboard DAC, or maybe even a Bluetooth enabled and battery powered DAC/Amp, give more option to the buyers and try to provide more feature for the price instead of just only concentrate on ‘Hi-Fi’ factor. It is almost 2019, I believe amazing sound quality is not enough to seal the deal, don’t get me wrong though, personally I like the approach and the sound quality leave nothing for me to complain but there is certainly some aspect that can be improved such as add a display, maybe change the volume knob, add an optical input etc. However, if audio quality and price to performance ratio is what you are looking for (me too), you shouldn’t look too far away, UDXA won’t disappointed you with its never tiring and ultra ‘Hi-Fiish’ sound.





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