SMSL M400 Balanced USB MQA DAC Review

[JohnYang1997]

Ah..as we see APx555 is not good enough for these devices. Performance is limited by AP's noise performance now.

 

[wwenze]

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.

Less of a voltage drop issue, more of an uneven frequency response issue if the load impedance isn't flat.

Also, more of a noise issue. Compared to e.g. 50ohm output-z this will give 26dB more noise from airborne radiation.

 

[amirm]

Forgot to post thermal stability:

 

[amirm]

Less of a voltage drop issue, more of an uneven frequency response issue if the load impedance isn't flat.

Hard to imagine load impedance in pre-amp not being flat in audible band but I probably should measure to be sure.

 

[wwenze]

Probably not an issue in majority of cases

But mix it with more chi-fi, or should I say ebay-fi or aliexpress-fi and the chances of problem becomes higher. Like this aliexpress-fi power amp based on IRAUDAMP7S which the reference design manual stats no more than 600ohm of source impedance.

https://www.aliexpress.com/item/329...earchweb0_0,searchweb201602_,searchweb201603_

 

[Music1969]

Uhh what? This sounds concerning. Don't most DACs have a similar output impedance? This one is 5 to 10 times higher to hit better numbers elsewhere?

Do we have the output impedances of all the other >110dB SINAD devices?

 

[xarkkon]

Not catering to me personally but rather, trying to produce absolute lowest noise and distortion.

Too humble! I do think that you're one of the few reviewers out there that call measurements for what they are. It's so easy for companies to slide poor designs under marketing bs (ESPECIALLY for dacs). This place is the first place (that I know of) that called dacs out for what they are and helped me to make some really good purchasing decisions (Topping!) that I otherwise would not have known about.

 

[amirm]

Do we have the output impedances of all the other >110dB SINAD devices?

I have measured a couple in the past and it is usually in the 100 to 200 ohm range.

 

[3125b]

Impressive results.
Regarding the impedance question - thats the same thing that came up in the A90 thread all over.
Isn´t it normal at least for headphone amps to have 10 (Atom) to 25kOhm (Schiit Heresy) input impedance?

 

[amirm]

There are no standards for input or output impedance. It is just assumed that designers play nice with each other by making output impedance low, and input impedance high.

 

[vkvedam]

IMD is also excellent as well:

Thanks @amirm, nitpicking, did you mean to say <-140dB for spurious tones ;-)

 

[digicidal]

Thanks @amirm, nitpicking, did you mean to say <-140dB for spurious tones ;-)

I caught that too... not that -104dB would be "bad" or anything... but clearly this is far below that for anything but the signal tone.

 

[evrial]

Any audible difference with DX3Pro?

 

[Eetu]

Any audible difference with DX3Pro?

With DACs as good as the DX3Pro & M400 it's very hard to find audible differences. I would upgrade only if you want some extra features or if you're not satisfied with the usability etc.

In my opinion, the $800 would be better spent on upgrading speakers/headphones, room treatments or getting a calibration mic (if you don't have one already).

 

[CopperFox]

This design of passive LPF is in the datasheet of ak4499. But I would argue it's for paralleling the outputs. The noise performance of this particular implementation of 4499 is not too great (1.6uV)that a opa1612 buffer (0.2uV) would cause any degradation. Not even mentioning half of 4499 seems to be turned off (lacking half of the components for a complete 4499 implementation).

Anyone know if any of the desktop 4499 DACs uses both halves of the chip? How would it be on the Topping or Gustard dacs?

 

[JohnYang1997]

Anyone know if any of the desktop 4499 DACs uses both halves of the chip? How would it be on the Topping or Gustard dacs?

Everyone else it seems.

 

[escalibur]

@amirm Will you measure M200 as well?

 

[wargreymon]

@amirm For the output impedance part, do you mean that it will be harder to pair with another amp due to the 1000ohm? I am planning to get this DAC and later on ELAC Navis ARB 51 active speaker to pair with it. Not too sure if this will be a problem.

 

[sq225917]

No issue for me playing redbook alac on itumes and macbook pro.

 

[themystical]

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.

The output stage appears to be straight implementation of the recommendation in Figure 82 of the AKM4499 datasheet so I don’t suspect any foul play.
https://media.digikey.com/pdf/Data Sheets/AKM Semiconductor Inc. PDFs/AK4499_Feb2019.pdf