REVIEW/MEASUREMENTS: SMSL (S.M.S.L.) M100 Mk II Hi-Res DAC (USB, S/PDIF Toslink and Coaxial In, ESS Sabre 9018Q2C, below US$100)

 

[Disclosure: Over the years, I have measured and reviewed products I have either bought or borrowed from friends. The product discussed in this post was sent to me by Aoshida Audio for an honest review and impressions which I can keep to use. It would only be fair that I provide the free shipping and "lowest price guarantee" links to Aoshida if readers want to purchase this DAC or others discussed. Considering that a major part of my review process is objective in nature and standardized over many years, I trust that much of what I present will remain free of bias. Note that I will be selective of what I agree to measure/review of this nature - accessible and high fidelity products that might be of interest to readers, or more innovative devices will obviously be most appropriate for what I do.]

As you can see in the image above, today let's have a look at another very inexpensive DAC product from S.M.S.L. with high-resolution ability. Over the years, I have reviewed/measured other devices from this company including the SMSL A6 integrated amp, the SMSL iDEA DAC, and more recently I've been enjoying the SMSL SA300 Class-D desktop amplifier. These are examples of "accessible" audio products, well within the price range of basically any music lover, "audiophile" or not.

So it is with this DAC. The S.M.S.L. M100 Mk II currently costs less than US$95, needs little power, and accepts USB/TosLink/Coax S/PDIF inputs. As you can see, it's shaped as a rectangular prism. The size is smaller than the photo might suggest measuring at about 2 1/8" x 2 1/4" x 3 5/8" long, weighing around 0.5lb (250gm). The enclosure is aluminum with shiny plexiglass front panel; the package feel solid. Inside the box is an assortment of printed manuals in English, Chinese and Japanese along with a basic white USB-A to micro-USB cable.

Here's a view of the back:

Straight forward arrangement of inputs and outputs. There are 3 input ports - "IN 1" micro-USB, "IN 2" TosLink S/PDIF, and "IN 3" gold-plated Coaxial S/PDIF. Outputs are gold-plated stereo RCAs.

There's an "AUX POWER" port for 5V input if your device doesn't have enough power (for example, if you're plugging a small portable device through OTG USB cable) from "IN 1" or you're just using the S/PDIF inputs.

Note the PSE designation beside the FCC logo which apparently differentiates this externally from the previous Mk I model. PSE is a Japanese electrical certification.

The cuboid SMSL amp and DAC stack quite nicely and is space saving like this. The M100 Mk II DAC does not have a headphone output however, unlike the Topping DX3 Pro.

You can better appreciate the size of this little DAC sitting on top of my SMSL SA300 amplifier and the Topping DX3 Pro to the left. Notice that the 3-digit blue LCD display is showing "512" in this image and you can see the single power button lit up blue. This means it's playing back DSD512 from my computer currently (PCM transcoded to DSD in Roon). When playing PCM, the power LED is off, and when the DAC is turned off, the LED goes red for standby. The LEDs are by no means bright and I did not find it distracting at all in a dark room.

All changes to input and settings are done through the single power button. Long push turns it on/off. Quick single click cycles between the 3 inputs. Double click allows you to select which DSD or jitter filter (choice of 3 DSD filter settings, 9 DPLL jitter settings!). This might sound complicated, but really isn't in actual use. The little pamphlet that came with the DAC says nothing about the DSD filter or DPLL settings (but you can see the description in an updated version online here). I have never seen a DAC with this kind of 9-level PLL jitter setting before.

Internally, the device is based on the XMOS XCore 200XU208 microcontroller which is not uncommon among modern asynchronous USB DACs and the audio converter is the ESS Sabre9018Q2C. This DAC can handle up to 32/768 PCM input, and DSD512 native mode (download the M100 Mk II XMOS driver here). The ESS chip has been around awhile now so it'll be interesting to see how well SMSL has optimized the output quality of this very low power chip in a 2020/2021 product iteration. The previous Mk I version of this DAC was using the AKM AK4452 chip and the company literature suggests that this Mk II has improved components ("ultra low phase noise" crystals, low dropout voltage regulators, metal electrode leadless fact [MELF] resistors...) and achieves measurably better THD+N performance.

MEASUREMENTS:

As usual, while I've already spent time listening to this DAC and will present my impressions in the "SUBJECTIVE" section of this post, let's have a look at the objective performance first as per my usual convention. I believe objective results are simply the more enduring and meaningful sections of product reviews.

Let's do this. For the measurements today, we'll connect this DAC to my Raspberry Pi 3 B+ "Touch" streamer as source:

Raspberry Pi "Touch" running Volumio --> stock USB cable (power & data) --> SMSL M100 Mk II DAC --> 6' shielded RCA --> RME ADI-2 Pro FS R ADC --> USB cable --> Analysis/Measurement computer (Intel NUC 6i5SYH)

Notice that I also have my old Logitech Touch out on the test bench! Let's use that as the S/PDIF TosLink and Coaxial digital source to feed the SMSL to evaluate the non-USB inputs.

Starting with default settings of DSD Filter 1 "dF1", and DPLL "dP1" which presumably is the tightest level of jitter control according to the online manual, let's plug this into the digital oscilloscope and see how 1kHz square and sine waves look:

Looks great visually. As we can see, both channels are precisely overlaid demonstrating essentially perfect interchannel balance. Output is a clean 2.02Vrms. The symmetry of the square waves suggest the use of a linear phase filter setting.

While one can adjust the DSD filter and PLL settings (we'll talk more about this), the DAC as far as I can tell has one digital upsampling filter setting for PCM playback - this one:

SMSL is using an "orthodox" linear phase steep filter and not fooling around with minimum phase stuff - this is good IMO. Note that it maintains absolute polarity (unlike the Topping D10 a couple years back which inverted).

Now let's have a peek at the "Digital Filter Composite" [DFC] (based on Juergen Reis' discussion a number of years ago):

So we see that it's a moderately steep filter as expected from the look of the impulse response with a few beats of pre- and post-impulse "ringing". Notice that with the 0dBFS wideband white noise it does "overload" (clip) - not uncommon. The anti-imaging filter works well. We can see some intermodulation and ultrasonic harmonics from the 19 & 20kHz sine signal.

This is not the cleanest digital filter and probably reflective of limitations of the ES9018Q2C DAC chip itself.

With an appreciation of the "microscopic" waveforms and frequency domain limitations of the digital filter, let's see how this DAC measures using the RightMark battery of tests which would be more reflective of music playback quality.

RightMark 16/44.1 (USB):
These days, 16-bit audio is not even challenging anymore for modern DACs! However, since most digital music is still RedBook-quality, let's just make sure it looks good:

"DX3 Pro" is of course the Topping DX3 Pro. I've been told that due to the recent AKM factory fire, this dual-AKM AK4493 DAC is currently unavailable for awhile.

Like I said, 16/44.1 is boring these days. I don't think it should surprise anyone if I say that playing standard CD-resolution music is a piece of cake for any high-resolution capable DAC. When blinded and volume matched, I doubt anyone would be able to tell devices apart. This is in fact the suggestion from the blind test a few years back.

While the old SMSL iDEA did not perform as well for the stereo crosstalk and distortion characteristics (THD, IMD+N), notice that the SMSL M100 Mk II and the old iDEA exactly overlapped in frequency response. Guess why... Yup, it's likely because the SMSL iDEA was also based on the ES9018Q2C DAC chip though of less sophisticated design compared to the M100.

RightMark 24/96 (USB):
Okay, let's talk about real hi-res - 24-bits/96kHz:

On balance, the M100 Mk II performance looks good. Distortion characteristics certainly compare well to the more expensive Topping DX3 Pro. I included the RME ADI-2 Pro FS R Black Edition for comparison; notice that the RME DAC is using balanced output hence adding to the better performance all around.

Even though there are differences, it's important not to get too worked up about small variation that simply isn't going to make a huge audible change with real music. For example, we see that there's a little more 60Hz hum with the SMSL M100 Mk II but this is still down at -135dB!

Apart from that 60Hz hum, notice that the SMSL M100 Mk II is slightly quieter than the Topping D10 through the remainder of the audio spectrum. The M100's IMD+N graph is interesting in that there's higher distortion above 20kHz - not audible of course and this is not excess noise so will not cause problems with amps or speakers.

RightMark 24/192 & 24/384 (USB):

For completeness, here are the results for even higher PCM data rates. The maximum 768kHz samplerate is not available in the testing software.

It's typical to see a bit more noise at extreme sample rates (combination of the device itself and the measurement ADC) so nothing unusual here. Looks like the DAC can maintain the high-resolution performance without issue.

Harmonic Distortions (THD+N):

Let's look more closely into the harmonic distortion produced by this DAC. With a 0dBFS (2Vrms output) 1kHz sine wave, here's the high-resolution FFT:

Better than -102dB THD+N is certainly respectable performance! As with most DACs I've seen, the THD+N tends to be lower below 0dBFS, here's the FFT at -6dBFS:

I suppose I could have captured an even better result if I ran the Raspberry Pi/DAC on batteries which would also remove the 60Hz hum. At almost -105dB already, this is impressive for a sub-$100 DAC! Notice that the 2nd harmonic remains dominant in both graphs above. We can have a look further with level and frequency step tests:

Overall the harmonic distortion pattern looks good. Mostly 2nd harmonic (which adds "warmth" like vinyl, right? :-) across the audible spectrum with a -6dBFS signal.

If we now look at the level step graph starting from -120dB of a 950Hz signal, we see 2nd and 4th order harmonics predominating throughout with only the 2nd harmonic rising above the THD nadir after -20dBFS. No unusual harmonic distortion "hump" as seen in some older ESS DACs.

From the level step data, we can extract the DAC linearity:

It's basically flat until about -87dBFS, but even then only deviating by 1dB by -105dBFS output level.

DSD Performance:

These days, I don't know how many audiophiles listen to DSD content to any substantial amount. It has been awhile for me other than playing with PCM --> DSD transcoding.

However, many modern computer USB DACs have maintained this feature and we can quickly compare DSD playback with the 24/96 RightMark test signal converted to DSD64 and DSD128 to make sure high-resolution performance has been maintained:

Remember that conversion from and to DSD will result in a very minor loss in fidelity so the DSD results will be a little lower. Numerically the results look good, and indeed DSD reproduction is of high-resolution quality.

Standard SACD-resolution DSD64 is typically noisy beyond 20kHz as shown above. Using a source 24/192 test signal converted to DSD, we can see the relative benefits of higher rate DSD128 and DSD256 on reducing the ultrasonic noise:

The M100 Mk II will also accept DSD512 data but already we can see above that at DSD256, the DAC has reached the performance of native 24/192 PCM in noise level.

You might be wondering about the 3 different DSD filters offered by the DAC, named "dF1" to "dF3". Honestly, I did not find any significant differences in the measurements using the settings! In other DACs, I've seen settings change the low-pass filtering to reduce the amount of noise getting through particularly with DSD64. For example, years ago the TEAC UD-501 already had 4 DSD filter options. As such, nothing worth reporting with this DAC and those 3 options.

S/PDIF TosLink and Coaxial Inputs:

Up to this point, we've just been using the USB interface. The two S/PDIF inputs are capable of up to 24/192. Remember to power the DAC with a 5V power supply applied to the "AUX POWER" micro-USB. I used a 5V, 3A switching power supply which is usually paired with my Raspberry Pi 3 B+ for these measurements.

Let's just compare the 24/96 measurements between USB and these S/PDIF inputs:

Not much difference although numerically it looks like the Coaxial input was slightly noisier. The graphs will show this clearer.

As you can see, with the Squeezebox Touch sending the S/PDIF digital output to the SMSL M100 Mk II DAC, we're picking up on some noise with the coaxial interface. A reminder that the coaxial interface is electrical and devices will vary as to noise sensitivity without galvanic isolation. Again, let me remind you that we're still looking at peak noise levels below -120dBFS! By all means, use the Coaxial input. In contrast, the TosLink interface tracked the USB input quite well for low noise and similar distortion levels like the IMD+N sweep graph.

Jitter:

Finally, let's talk about the objective jitter performance of this DAC. Remember that in the menu there is a setting for "dP" from 1-9 which is supposed to change the "DPLL" level, which based on the description I presume means "Digital Phase Locked Loop".  The manual says "The larger number means the stronger range to adapt to jitter. The smaller number means the better performance against clock jitter". So does this means that the smaller the number - ie. "dP1" - should result in better jitter performance? Let's have a look.

Let's start with the USB interface:

Hmmm, two observations. First, that this DAC in the asynchronous USB mode is surprisingly not as well controlled in jitter performance as I had expected. Notice the sidebands especially in the 24-bit test where ideally the noise floor should be flat. No need to get hysterical about this though because we're still looking at below -120dB sidebands in a synthetic test designed to worsen jitter effects. Regardless of "dP" 1/5/9 setting, I see no difference.

Okay, so maybe the DPLL setting is not meant to be used with USB. How about with the S/PDIF inputs? Let's start with the TosLink:

As expected, the jitter is higher in level than asynchronous USB. Notice again that changing the "dP" level made no difference to the J-Test spectrum.

Finally, here's the Coaxial S/PDIF input:

Hmmm... Unfortunately it's worse than TosLink. This is rather surprising in that typically coaxial has better bandwidth, and can be more stable at higher sample rates.

Clearly, not the best S/PDIF jitter performances I've come across. For an example of a DAC with excellent jitter rejection, fed with the same Squeezebox Touch S/PDIF outputs, check out the Oppo UDP-205's results.

With Enhanced Digital Output (EDO) installed on my Squeezebox Touch, I can confirm that 24/192kHz was supported by both TosLink and Coaxial inputs. TosLink can be more challenging to implement for higher samplerates and I did not hear any issues at all listening to 24/192 over TosLink for about an hour or so.

So, a few jitter-related technical issues to bring up which I'll highlight in the Summary below.

SUBJECTIVE:

As usual, I listen to the review device for a few evenings before running measurements on my test bench so I'm not biased by the objective results when listening. I have never found "breaking in" to be an issue with solid-state DACs like these (although warm-up can produce audible effects even with solid-state components like the Pass ACA) so no need to run music through for days on end before listening.

Here's the little DAC in my listening room, connected to and also powered by the Raspberry Pi 4 "Touch" streamer's USB port running RoPieee, streaming through gigabit ethernet from my Roon server in another rooom:

This SMSL M100 Mk II DAC is small.

Notice that it's sitting to the left of my RME ADI-2 Pro FS R Black Edition. For context, remember that the RME is both an ADC and DAC and costs close to twenty times that of the little SMSL! Underneath, we have the Oppo UDP-205 which of course has been discontinued and these days is only available at heavily scalped prices but the MSRP back in the day would have been fourteen times the price of the SMSL M100 Mk II! Both the RME and Oppo I have connected to my preamp through balanced XLR as opposed to just RCA for the SMSL. Furthermore, you can see my tried-and-true TEAC UD-501 reference with its MSRP back in the day of over six times the SMSL.

In this context, how does the little <US$100 SMSL hold up? Would it surprise any of my readers that the answer is "remarkably well!"?

I mentioned awhile back that during the pandemic, my wife got into Korean dramas... Well, the picture above shows that I was streaming the soundtrack to Crashing Landing On You (2020). Not bad at all if you're into some KPop. The track "Give You My Heart (마음을 드려요)" by IU is a sweet one. Another good Korean drama soundtrack I listened to recently is the one for It's Okay to Not Be Okay (2020). The albums sound clean, precise with good center focus for vocals. The DAC has no issues at all with full-frequency reproduction. I love the synthesizer instrumental "Her World (그녀의 세계) (Moon Young’s Theme)" (on It's Okay... soundtrack) with a combination of "clinically precise", at times jarring, even quizzical emotions the track evokes which is appropriate for the character it represents in the show.

Recently I've been listening to Bruce Springsteen's latest Letter To You (2020) which is reminiscent of "classic" Springsteen albums of many moons past. The drum intro on "Ghosts" sounds great through this DAC, temporally "tight", and reaching appropriately deep. Springsteen's vocals sound good on the slower, quieter tracks like "One Minute You're Here" (nice vocals with guitar, and piano for that first minute) and the fist part of the closing track "I'll See You In My Dreams" before the E Street Band lets loose; very good reproduction of nuances and "microdynamics".

For some DAC calisthenics, it was a blast listening to the two 300 movie soundtracks (300, and 300: Rise Of An Empire) with their Middle Eastern inspired themes (I love "History of Artemisia" on Rise...) and the at times intense, yet well-orchestrated chaos! The latter would be a track like "To Victory" (300) with its complex layers of vocals, sound effects, exotic, synthetic and sampled instruments. Poor DACs over the years muddle up the sound whereas a good DAC will lead the listener through the various parts as they enter and exit the track, maintaining good listener engagement. The sound from this DAC remained resolute throughout "To Victory" and others on these albums and I didn't get the sense of excess harshness nor feeling fatigued after listening for awhile.

If you're interested in male vocals, and enjoy a little bit of the eclectic, dramatic, even operatic, have a listen to Benjamin Clementine's At Least For Now (2015). Check out track 1 - "Winston Churchill's Boy". Awesome piano accompaniment and overall how "spacious" it sounds through a good audio system. Make sure to listen as the percussion comes in at 2:10. Very good through the SMSL M100 Mk II.

As usual, I'll also listen to some of my "audiophile" playlist songs like "Time" (Dark Side...) to have a sense of the "imaging" of the clocks and bells - yes, this DAC did a great job with maintaining the illusion of sound around the listener. The deep deep bass of "Tibetan Drama Dance" (Mystical Scent [神香]) was rendered well (make sure you have speakers/sub that approach 20Hz to appreciate the "gravity" of this music). And of course Nils Lofgren and his audiophile nugget "Keith Don't Go (Ode to the Glimmer Twin)" from Acoustic Live (1997). Great dynamics, excellent soundstage precision, nice audience participation, and of course guitar detail and speed.

One evening when all was quiet (low ambient noise) I did a volume-matched A/B comparison with the RME ADI-2 Pro FS R (switching between RCA and XLR inputs) with DSP turned off using a variety of standard and hi-res recordings. The impression I have is that the RME was able to extract a little more low-level detail and deeper spatial depth. Benjamin Clementine sounded more "present" in the room, his piano was more localized and the notes decayed with more finesse through the RME. These are nuanced and subtle, certainly not obvious differences I would notice without quickly switching and concentrating on the sound. Remember, these days frequency response is basically flat with good DACs, the differences are not to be found with simplistic claims like "deeper bass" - this is not an issue. IMO, listen for the nuances of space and low-level details.

While I found the sound to be very good, one small annoyance with the M100 I noticed was the presence of a soft "click" when the DAC switched samplerate.

Streaming the excellent Soul (2020) soundtrack.

For fun, remember that because this is a low-power DAC, one could just run the device on 5V USB battery power for hours as in the picture above. I also was running TosLink from the Squeezebox Touch to the DAC for galvanic isolation. While objectively I know that jitter is higher with the S/PDIF interfaces in general, I could not hear a significant problem.

Subjectively this is a nice-sounding low cost DAC with hi-res abilities. There is no way I would be able to tell that this DAC costs at least 6 times less than the "cheapest" of my other DACs (never mind <1/10 the price of others!) in a blind listening session. To me this is a nice example of the "point of diminishing returns" for subjective sound quality with DACs these days. I'm saying this even knowing the objective limitations above as I complete this review.

SUMMARY & THE BOTTOM LINE:

Clearly, in the last decade, the market for high-resolution DACs has changed substantially. High-fidelity sound is clearly no longer the sole provenance of "Hi-End" (High-Priced!) products.

This SMSL M100 Mk II DAC is an RCA-out, <$US100, USB-powered device that accepts USB, TosLink and Coaxial S/PDIF digital inputs performing to verifiably high-fidelity specifications although not without some technical imperfections. It can accept up to extreme 32/768kHz PCM input and DSD512 (22.5792MHz) data rates through USB and up to 24/192 over the S/PDIF interfaces. Objectively, when used as a USB DAC, we're seeing flat frequency response, verifiably better than -100dB THD+N (<0.001%) distortion and noise. Despite being an "entry level" DAC, the sound quality is certainly more than good enough for music reproduction. It reproduces standard CD-resolution 16/44.1 with ease and I would argue just as good as any other high-fidelity DAC regardless of cost. As for resolutions above 16/44.1, this will also do the job although not to the same degree as more expensive products.

At this price point and audio quality, is there anything more I would ask of this DAC? Well, as a "more objective" audiophile, here is my list of annoyances and technical findings I think SMSL should ask their engineers to review. I don't know if the firmware is upgradeable, but maybe see if improvements are possible:

1. See if there's a way to suppress that soft "click" sound when samplerates change.

2. Are the DSD (1-3) filter and DPLL (1-9) settings actually working? As far as I can tell with this unit I have, the settings made no difference.

3. Double check the jitter performance. It seems higher than what I would expect. Especially examine the jitter performance for the Coaxial input which seemed excessive. Maybe this has to do with the DPLL settings in point 2? (Remember that I don't put a lot of weight on the audibility of jitter, nonetheless I do appreciate excellence in technical performance.)

4. If there is a way, I would love to see better digital filter performance with improved intersample overload protection. Not as high in priority as the above points but nice to have on the technical wish-list.

Apart from the above, I suppose USB-C connectors would be good these days, but in practice micro-USB is fine and I suspect keeps the price lower.

Obviously, going beyond the entry-level price point, one might want to spend more money on other features like a good headphone output, maybe a DAC with physical volume controls, Bluetooth wireless, etc. These days, if one needs higher resolution performance, I would recommend getting a DAC with balanced XLR outputs, and obviously one's audio system should also be capable of the ultra-low-noise performance if doing so.

The obvious comparison DAC at this price point and feature set would be the Topping D10 which I reviewed before, and since then updated to the Topping D10s (slightly higher price ~US$110). What I like about the D10s is the ES9038Q2M DAC with to-be-expected excellent objective performance. However, when I think about what most users might need, I think the SMSL M100's TosLink and Coaxial S/PDIF inputs would be more useful than the D10(s) S/PDIF outputs. The SMSL's power button to put it into standby is nice to have, and the higher DSD512 and 768kHz PCM inputs compared to the Topping are little extras for those who want to tweak or experiment with these ultra-high-samplerates (eg. PCM --> DSD512 upsampling). Another low-cost DAC to consider would be the Schiit Modi 3+ at the $100 mark featuring the AKM AK4490 chip (max 24/192, no DSD, USB + TosLink + Coax inputs).

Remember that the DAC market is very competitive, so looking a little higher up in price, there's the Topping E30 (~US$150) with AKM AK4493 and S/PDIF inputs or the similar SMSL Sanskrit 10th Mk II with remote control both looking good.

If you look even lower down in the price range, see basically headphone DACs like this which are not up to the standard of this SMSL. Something like the AudioQuest Dragonfly Red is OK for headphone out but I'm just not a big fan of the price-to-fidelity (some Dragonflies measured and discussed here).

Bottom line. The SMSL M100 Mk II is a small form factor cuboid-shaped DAC that's sub-$100 and sounds good as a USB DAC with the flexibility for S/PDIF Toslink/Coaxial inputs. I would recommend staying with the USB input primarily if objectively lower jitter is important for you. If the unit I have here is a general indication, don't bother with the DSD filter and DPLL menu settings.

I think many budget-conscious music lovers and "beginner audiophiles" will appreciate the excellent subjective sound quality and flexible hi-res/high-fidelity playback capabilities. At this "bang for buck" price range, combined with an inexpensive Class-D amplifier like the matching SMSL SA100 or maybe their SP100 headphone amp (each around US$70), plus some good desktop speakers or headphones, I suspect one will achieve a very nice sounding mini-system.

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

Whether it's friends lending me gear or in this case Aoshida Audio sending the product, thanks for the opportunity to listen and objectively critically evaluate the gear.

I don't know if others see it this way, but in an age where purchases have become much more of an online experience, in a way, I think it's a form of "customer service" that sellers seek out independent and objective reviews especially when one is dealing with increasingly technically literate enthusiasts.

Enjoy the music and stay safe everyone...