Stoner Acoustics UD125

General Information

https://stoneracoustics.com/ud125/

Description​

Fellow friends and fans, thank you all for your support on our UD series DAC. This product remains an important identity and staple of our company.

Over the years, the UD has always been designed primarily to function as a pure line out DAC and requires an external amplifier for demanding applications. We understand the need for flexibility and so during the next design phase we asked ourselves an important question, can we actually produce a convenient product that can cover all bases (both line out and amplification) without sacrificing performance and cost? The UD125 was thus created.

Dual Use
The UD125 output is dual use. The output is designed to function as a line out for external amplifiers and to drive most modern demanding headphones.

High Power Output
The UD125 is powerful and goes up to 350mW each channel.

Precise and Accurate Digital Attenuation
The UD125 uses a very precise and accurately tracked digital volume control and allows for minute adjustments on even the most demanding IEMs. You can even use it as a pre-amp for your larger speaker amplifiers.

Selectable Digital Filters
We understand that you enjoy tweaking your sound, so we are offering up to 4 digital filter settings for you to tune your system with.

Plug and Play
No messing about with drivers and settings. You can carry the UD125 alongside with your favorite headphones and enjoy high quality sound from any supported digital medias.

Android USB OTG Support
The UD125 works with your modern Android Smart Phone too! Just make sure that your phone has sufficient current support for USB OTG. (Contact us for more information)

Specifications​

Features:
Savitech SA9037 USB Audio Processor
AKM AK4490 High Performance DAC
TI TPA6120A Dual Channel High Power Amplifier
USB Audio Class 1.0 24 Bit/96 KHz
High Voltage Output at 4.88 Vrms Line Output
High Power Output at 2 x 350mW Low Impedance Output
0.5 dB/Step Digital Attenuation
Selectable Digital Filters (4 settings)
Credit Card Sized Chasis

Package Includes:
1 x Stoner Acoustics UD125
1 x USB 2.0 Mini USB Cable
1 x Carrying Pouch
1x 1 Year Limited Warranty

Weight and Dimensions:
58mm (Width) x 89mm (Length) x 17mm (Height)
90 grams

Latest reviews

CK Moustache

100+ Head-Fier
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/




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"]





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.

- - - - - - - - - - - -

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:

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