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Amirm M400 DAC Review
Release Date:2020-06-06 Views:3167

This is a review and detailed measurements of the SMSL M400 balanced and unbalanced DAC. It was kindly sent to me by the company. The M400 costs US $810 from prices I see online.

The M400 design has been upgraded with a larger, more clear display and a Plexiglas upper cover:


There is the usual remote control you see across a wide range of products from China. I like it normally but in this instance, it did not have proper key debounce and as such, it would repeat the key someones making it harder to make selections.

The back panel is as you expect with the exception of missing AES/EBU balanced digital XLR input:


There is good bit of heft to the unit, giving a feeling of quality.

As you see there is also bluetooth input which I did not test.

MQA decoding is included although I did not test that.

DAC Audio Measurements
As usual we start with our dashboard of 1 kHz and to be fair, with devices that output more than 4 volts balanced, I adjust the output down to get 4 volts:



Wow, this is excellent performance. Noise floor is about to fall off the chart on FFT. Distortion is less than -135 dB and as low as -140 dB in one channel. With best case hearing threshold being around -115 dB, we are way, way past transparency here.

SINAD which is a score that sums distortion and noise is much lower than the distortion, limited by the noise output of the M400 and my analyzer at 121 dB. Still, we have a tie for top spot of all DACs ever tested regardless of price or configuration:




Letting the DAC go to its maximum output improves the SNR of both the analyzer and DAC allowing even better SINAD:



We can see it also as we step through the levels:



RCA output is almost as good:




Signal to noise ratio as stated, is more or less at the limit of what we can measure:



Linearity is absolutely perfect even if I reduce the output to 4 volts:



Multitone follows suite with also superb level of intermodulation distortion:



IMD is also excellent as well:



The very low noise though allows us to see a tiny step up in intermodulation distortion at levels higher than -40 dB.

Jitter over USB is excellent:



Toslink is not in the same league though:



Company says this is due to the connector and better ones are no longer in production. Coax input is better with far less jitter although still a step behind USB. Either way, don't let the graphs mislead you into thinking there is an audible problem here. Even with Toslink it should not reduce audible performance.

Using 90 kHz bandwidth so we can capture harmonics of 20 kHz tone, we have very good performance but not perfect:



Reason for that is that the reconstruction filter while better than many DACs, still allows out of band signals bleed through:





Nothing audible to worry about but my plea continues for DAC chip companies to provide better attenuation of out of band signals.

Output Impedance
I did not get a chance to measure output impedance but from data I have seen elsewhere, it rises to well over 1000 ohm. This is about 5 to 10 higher than it is normally. An output buffer stage has been eliminated to improve measured performance with the cost being that output impedance goes up. When you think of pairing this DAC with headphone and power amplifiers, make sure their *input* impedance is at least 10 times higher or 10 kHz and above. You should be OK with many products but with others, you may see a voltage drop. Seeing how M400 has more than 4 volts output anyway, maybe this is not a concern in practice.

Conclusions
We have another "instrument grade" DAC here from SMSL in the form of M400. Performance is beyond question, landing at the top of the class. Price has gone up with it as well but there is no free lunch. 

On a slightly down note, it seems the race for the top place in our ranking is resulting in some design decisions such as removal of output buffer and increase of output impedance. I am not too happy about this but haven't decided what to do about it.

Anyway, I am happy to recommend the SMSL M400.

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As always, questions, comments, recommendations, etc. are welcome.


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