Audio science review SMSL SU-9n Review (Balanced Stereo DAC)
This is a review and detailed measurements of the SMSL SU-9n balanced USB stereo DAC with Bluetooth support.
From the outside, the SU-9 looks like the recent DACs from SMSL:
And from the back side for that matter:
A side story. When I started to test the SU-9n, I could not get one unbalanced channel working. I tried everything but one channel would not work. Balanced was fine. Later on I went to test the Coax input and it was then that I figured out that the “non working” channel cable was hooked up to the Coax digital input! I had hooked it looking from above and just assumed the RCA connectors would be next to XLR connectors.
Anyway, good to see in-built AC mains power supply despite the small form factor.
SMSL SU-9n Measurements
Starting with XLR balanced output, there was more output than my standard 4 volt so I adjusted the volume to get it close:
This is exceptional performance with distortion almost shrinking down to -140 dB! This places the SU-9 in #3 position of some 350 DACs tested to date:
Performance using RCA out is almost as good:
Distortion is even lower but noise is a bit higher and hence slightly lower SINAD.
Since there is more output to be had at full volume, I ran a level sweep:
Performance keeps improving so if your amp can take it, let it go to max volume!
Dynamic range is superb:
Linearity is exceptional:
Multitone performance follows the same:
Jitter performance is just as good with USB but there is a bit of jitter over coax:
Don’t ask me about optical input. I sent out my Toslink cable to the store to get some milk and it has not come back….
I was surprised to see two new “Customized” filters in the already large set provided:
I have no use for them though give the fact that they roll off early and don’t cut out much. I looked in the manual but there is no documentation on them.
The filter choices makes a difference in THD+N vs frequency due to it measuring “out of band” spectrum of the DAC:
Lastly here is our IMD vs level:
The classic signature ESS DAC chip IMD “hump” is there, albeit, very much reduced to be a non-issue.
Conclusions
Yes, yet another exceptionally good DAC. I know some of you are going to complain about us testing so many of them. Imagine if the situation was reverse and most of what we tested was junk. Would you be happier then? I don’t think so. 
Count your blessing that you have so many choices and how barriers are being broken every few weeks and months in lowering noise and distortion.
I am happy to recommend the SMSL SU-9n.
