Stoner Acoustics UD125

Link to my review and measurement index thread where one can also find a full review overview, more information about myself as well as my general-ish audio and review manifesto: https://www.head-fi.org/threads/956208/

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I only give full stars. My ranking/scoring system does not necessarily follow the norm and is about as follows:

5 stars: The product is very good and received the "highly recommended" award from me.

4 stars: The product is very good and received the "recommended" award from me.

3 stars: The product is good/very good, but not outstanding/special enough to get any of my two awards. ["Thumbs Up"]

2 stars: The product is only about average or even somewhat below that and somewhat flawed/flawed in some areas. [neither "Thumbs Up" nor "Thumbs Down"]

1 star: The product is bad/severely flawed to outright bad. ["Thumbs Down"]

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Stoner Acoustics UD125


Source:

Review sample.


Miscellaneous:

Comes with a very nice storage case and cable.

It’s great to have the user manual basically printed onto the case’s top plate.
Compact design.
I sort of like that aside from a graphical operation manual, the top also features a simple schematic graphic of the internal sound-related component.
Made of metal.
Build quality seems really good.
Surprisingly light.
Unfortunately the DAC doesn’t have any rubber feet.

3.5 mm headphone output on the front, along with a status indicator LED (different colours for the digital filters as well as minimal and maximal volume warning) and a joystick-like digital volume rocker that can be pushed in to change the digital filters.
Mini USB input on the rear.




Sound:

AKM AK4490 DAC chip; Texas Instruments TPA6120 amplifier chip.

Volume Control:

Digitally controlled volume with 256 attenuation steps with precise 0.5 dB per step along the entire attenuation range result in the ability of listening just barely above the audible threshold even when using extremely sensitive in-ears is possible, which is very nice.

While it is nice that the last volume (as well as digital filter) setting is remembered, there is unfortunately no volume indicator, which is somewhat sad.
No accelerated volume adjustment wherefore large adjustments take some time.

Pushing in the volume rocker for at least one second mutes the output.

Hiss Performance:

There is some clearly audible hiss with very/near extremely sensitive in-ears (e.g. Ostry KC06A, Shure SE846, Pai Audio MR3) and fairly high amount of hiss with extremely sensitive in-ears (Campfire Audio Andromeda). Ultimately less hissy than the iBasso DX50, HiFime 9018D, Shanling M2 or iBasso DX80, but also not nearly as quiet as devices such as the iBasso DX200, iBasso DX90, Cowon Plenue 2, Cowon Plenue D or FiiO Q5.
Using still sensitive but less extremely sensitive in-ears such as my Ultimate Ears Triple.Fi 10 or Ultimate Ears Reference Monitors, hiss becomes very little, but is still audible.

As a result, I wouldn’t recommend the UD125 for sensitive in-ears.

Frequency Response (no Load):


FR unloaded

Flat and linear as it should be, but with a small roll-off towards 20 kHz that is however negligible.

Frequency Response (no Load; all of the four Digital Filters):


FR unloaded Digital Filters

Output Impedance (Ultimate Ears Triple.Fi 10 as Load):


FR loaded – Ultimate Ears Triple.Fi 10

Based on the frequency response deviation, the UD125’s output impedance is calculated to be around only 0.1 Ohms, which is truly excellent.

Subjective Listening Impressions:

Nothing bad to report here.

Subjectively a bit of softness in the lows and perceived “smoothing” of the high frequencies when using in-ears; likely caused by the high noise floor.
No audible difference to other flat measuring devices anymore to me when used with full-sized headphones.

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Comparisons:

HiFime 9018D:

Neither DAC has got any rubber feet.
The 9018D is slightly more compact and even features a digital output whereas the UD125 comes with a practical storage case.
While the 9018D has got two digital filter settings that can only be switched when turning on the device, the UD125’s digital filters can be changed any time.

Whereas the Stoner Acoustics DAC doesn’t have any sort of real volume indicator, the HiFime has got a very convenient LCD screen that shows the volume and sample rate (and even the screen’s backlight brightness can be adjusted).

Both feature 256 precisely digitally controlled volume attenuation steps à 0.5 dB.

Both have got a perfectly low output impedance of around 0.5 Ohms.

Neither DAC comes close to hiss-free perfection with sensitive in-ears, but the UD125 is ultimately somewhat less hissy (audible hiss with my Ultimate Ears Reference Monitors on the HiFime and only very mild hissing the Stoner Acoustics).

Subjectively when using in-ears, the HiFime appears a bit “harder”/”more direct” in the highs compared to the softer/smoother UD125. The Stoner Acoustic’s low-end presentation appears slightly softer when used with multi-BA in-ears.
Perhaps very slightly larger (especially deeper) soundstage rendering on the UD125 with in-ears.




Conclusion:

Perfect output impedance, highly precise digitally operated volume control that also allows for listening just barely above the audible threshold. Unfortunately quite hissy with sensitive in-ears. A volume indicator would have been nice as well.


Photos: