• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

S.M.S.L PO100, PO100 PRO & PO100 AK - Measurements (Digital Interfaces & DAC)

VintageFlanker

Master Contributor
Forum Donor
Reviewer
Joined
Sep 20, 2018
Messages
5,105
Likes
20,437
Location
Paris
S.M.S.L PO100, PO100 PRO & PO100 AK Measurements

Main.jpg

Hey folks,

It is time for my very last review of the year. A very special one, as there are three products to be measured today ! S.M.S.L released earlier this year the PO100, a tiny and fairly cheap USB to S/PDIF interface. Later in 2022, they launched the PO100 PRO and PO100 AK. The PO100 MSRP is 39$, but this one seems to be discontinued by the time of this writing. PO100 Pro costs 69$, while PO100 AK is priced at 89$ (a bit more expensive in EU for each). I will cover their respective features below. I bought all three myself on Amazon.

This review has two purposes, checking the eventual presence of signal degradation that would be imputed to the interfaces themselves, and evaluating the PO100 AK as a standalone DAC. This one in particular promises a lot. AK4493 chip, with 116dB SINAD claimed, that puts it against the pricier Topping D10S: exactly the same features in a smaller form factor, with the addition of MQA support.​

Front.jpg


Each PO100 is very well-built, with body full of aluminum and only the top side in acrylic. I am not a fan of the latter, as it is a real fingerprint magnet. You can guess their very tiny form factor when looking at the size of connectors. PO100 PRO and AK are sized the same, while the AK is a touch heavier. Through S/PDIF, three support up to 24Bits / 192kHz PCM & DSD64 (DoP). The PO100 PRO adds MQA decoding, but It doesn't appear to be compatible with regular optical and coaxial outputs. Same for the PO100 AK, for which MQA seems working with its DAC only. Both PO100 PRO and PO100 AK do add UAC USB support, which means that you can plug them directly to a Sony PS5 (and PS4?) or a Nintendo Switch.

PO100 PRO & PO100 AK are advertising the implementation of a new generation XMOS XU316 USB chip, while there is no information about the XMOS in the regular PO100.​

Rear.jpg


One thing shared by all three units is the USB-C input (on the back for the PO100) and both optical and coaxial out, which by the way are working simultaneously, for those who are asking. All are USB auto-powered and OTG compatible. I personally like the choice of USB-C over regular USB-B, that helps to get very compact units and easier cables pairing for laptops and smartphones. PO100 PRO adds HDMI I2S output, that brings PCM support up to 32bits / 768kHz plus DSD512 and probably MQA. PO100 AK supports the same through its DAC and (single ended) analog outputs. At last, PO100 PRO does have two switches on its bottom, one for I2S Mode1/2, the other for UAC1/2.

I2S output will not be tested today, as my reference DAC does not have the proper input for it. However, I could try a few tests with my Matrix Mini-i Pro 3 later. Same for MQA support, as I would need proper MQA test tones to do so.​


Measurements

Disclaimer: Measurements you are about to see are not intended to be as precise or extensive than what you get from a 30k€ AP. There is obviously both hardware and software limitations here, so not quite apples to apples comparison with Amir's testing. Still, this data is enough to have a pretty good idea if the gear is bad or not, stellar, broken, or sub-par...

- ADC : E1DA Cosmos (Grade B). Minimum phase filter. Output voltage is measured separately, using a DMM with a 0dBFS 1kHz tone.
- Software : RMAA 6.4.5 PRO, Multitone Loopback Analyzer 1.0.60 and REW V5.20.13.
- Method : 8 runs for each test, then I choose the closest to the average. All regular tests are running 24bits / 44.1kHz, except for Jitter and Multitone ones.
- PO100, PO100 PRO, and PO100 AK, are all used as USB to S/PDIF converters (both optical and coaxial), connected to S/PDIF inputs of a Topping E70 balanced DAC. What is intended to be measured is their respective impact on the final analog output. All three use the same USB driver from S.M.S.L
- PO100 AK, as a DAC: Measured separately with its analog output (USB in, RCA out) at full scale: 2.11Vrms @1kHz.​

Rear2.jpg

As a reference/performance target, I use a Topping E70, through USB input, balanced out at full voltage :
Test ref 5V.jpg


Summary
Test
Reference (E70 USB)
PO100 Toslink
PO100 Coax
PO100 PRO Toslink
PO100 PRO Coax
PO100 AK Toslink
PO100 AK Coax
Frequency response (from 40 Hz to 15 kHz), dB
+0.02, -0.02​
+0.01, -0.02​
+0.01, -0.01​
+0.01, -0.02​
+0.01, -0.01​
+0.01, -0.02​
+0.02, -0.02​
Noise level, dB(A)
-125.2​
-125.3​
-125.2​
-125.4​
-125.2​
-125.3​
-125.3​
Dynamic range, dB(A)
124.6​
124.6​
124.6​
124.7​
124.7​
124.6​
124.6​
THD, % (REW)
0.00002​
0.00003​
0.00003​
0.00003​
0.00003​
0.00003​
0.00003​
THD+N, dB (REW)
-121.8​
-121.7​
-121.7​
-121.7​
-121.7​
-121.7​
-121.8​
IMD + Noise, %
0.00029​
0.00029​
0.00030​
0.00029​
0.00029​
0.00029​
0.00029​
Stereo crosstalk, dB
-126.1​
-125.7​
-125.3​
-126.0​
-125.9​
-125.5​
-125.6​

Frequency Response
fr.png


Noise Level
ns.png


Dynamic Range
dr.png


THD + Noise
thd.png


Intermodulation Distortion
imd.png


Crosstalk

ct.png


Here you go. I am pleased to save a lot of time commenting on the results, since all DUTs 100% fulfilled their task: convert USB to S/PDIF with no loss. Period. There are extremely minor to no difference at all. The minimal dissimilarities you see in numbers are most likely imputed to common run-to-run variations. After hours of repeatability, I would easily proclaim all three units to perform the same. With a bit of nitpicking, both crosstalk and frequency response did show very small changes. For the latter, we are talking about 0.04dB difference past 15kHz at both extremes. To state the obvious: no one on earth could hear that.

While I did not expect to observe much of a difference in regular tests, maybe, I could find more dissimilarities when it comes to Jitter...​


Jitter
(48kHz, 1-24kHz bandwidth, 16 averages, 262K FFT)

PO100
Jitter Optical PO100.png
Jitter Coax PO100.png


PO100 PRO
Jitter Optical PO100 Pro.png
Jitter Coax PO100 Pro.png


PO100 AK
Jitter Optical PO100 AK.png
Jitter Coax PO100 AK.png

Hum... nope! Nothing significant that could affect audibility. Coaxial brings a little more sidebands, but all three interfaces provided, again, the same performance. Or at least, we have reached the absolute limit of the E70 itself. For instance, its performance within USB is absolutely similar under my bench, if not identical.

But now, it is time for something more interesting, we have a tiny, good-looking DAC to measure...​


PO100 AK - DAC Measurements
Rear DAC.jpg

Edit March 2023: @SMSL-Mandy reacted to this review and suggested that this tested unit could be defective. S.M.S.L offered to send me another product, which I tested here:
These are the initial measurements of the DAC:​

S.M.S.L PO100 AK DAC Summary
Test
Results
Rating
Frequency response (from 40 Hz to 15 kHz), dB
+0.04, -1.28​
Mediocre
Noise level, dB(A)
-117.0​
Excellent
Dynamic range, dB(A)
116.9​
Excellent
THD, % (REW)
0.00021​
Excellent
THD + Noise, dB (REW)
110.7​
Excellent
IMD + Noise, %
0.00078​
Excellent
Stereo crosstalk, dB
-102.1​
Good
IMD at 10 kHz, %
0.00048​
Excellent

REW FFT
REW FFT THD+N.jpg

Frequency response

fr.png
Left​
Right​
From 20 Hz to 20 kHz, dB​
-5.09, +0.04​
-5.08, +0.05​
From 40 Hz to 15 kHz, dB​
-1.28, +0.04​
-1.27, +0.05​


Noise level
noise.png
Left​
Right​
RMS power, dB​
-117.8​
-116.6​
RMS power (A-weighted), dB​
-117.7​
-116.3​
Peak level, dB FS​
-97.7​
-98.8​

Dynamic range

dynamics.png
Left​
Right​
Dynamic range, dB​
+117.7​
+116.5​
Dynamic range (A-weighted), dB​
+117.6​
+116.1​

Intermodulation distortion

imd.png
Left​
Right​
IMD + Noise, %​
0.00076​
0.00081​
IMD + Noise (A-weighted), %​
0.00038​
0.00044​

Stereo crosstalk

cross.png
Left​
Right​
Crosstalk at 100 Hz, dB​
-101​
-103​
Crosstalk at 1000 Hz, dB​
-100​
-102​
Crosstalk at 10000 Hz, dB​
-108​
-109​

Intermodulation Distortion (swept tones)

imdswept.png
Left​
Right​
IMD + Noise at 5000 Hz,​
0.00043​
0.00051​
IMD + Noise at 10000 Hz,​
0.00042​
0.00050​
IMD + Noise at 15000 Hz,​
0.00047​
0.00054​


OK, as opposite to S/PDIF interfaces results, there is a lot to talk about here! We start with the REW FFT. Left channel gives me 116dB SINAD, which not only is right on manufacturer's specs, but anyway extremely good for a 89$ unbalanced DAC ! Then, we have to talk about the other channel... what the heck is going on there? First, the Right is both noisier and shows much more distortion (20dB difference at 2nd harmonic). Second, results with that one were very inconsistent runs after runs. I stuck with about 105dB SINAD as an average, but it gave me up and down FFT figures between 103 and 108dB! I did not see such instability over all the DACs I measured so far, that I even questioned a malfunction with my Cosmos ADC, my wiring or the software.... So I launched several tests with other DACs, balanced or single-ended, and got very cohesive results every time, as expected. Back to the PO100 AK, I still got the same mismatch between Right and Left over and over. Why such a difference? I have no clue. One hypothesis could be the proximity of the Right channel to the USB-C input, which would barely be any excuse and a dramatic fail in design anyway.

In fairness, we are talking about 103dB (worst case) to 116dB THD+N performance, that could be transparent enough for most people. But what about the rest? The L/R gap is indeed observable in many RMAA tests. Seeing the crosstalk performance, it remains kind of OK, but far from the best DAC I measured. But this is far from my biggest concern with the PO100 AK: The frequency response is way off. We get almost 5.1dB missing amplitude at 20kHz for both channels, which is nowhere near acceptable in my book.

After loosing a hell of a time triple-checking my data/process to investigate about the mismatch, the rest of the tests can be done somewhat faster. What about Jitter performance?​


Jitter
(48kHz, 1-24kHz bandwidth, 16 averages, 262K FFT)

Jitter Left.png
Jitter Right.png


Hum... not that great, honestly. Sure, the Left channel is again better, but I cannot ignore the spikes and sidebands which are not supposed to be that apparent in a properly designed DAC (price is not an excuse). Fortunately, these are too low in amplitude to be audible, even with the quite bad results out of the Right channel.​


Multitone 64
(192kHz, 20Hz-22kHz bandwidth, 10 averages, 262K FFT)

Multitone Left.png
Multitone Right.png

The story does not change for the last Multitone plot. The difference is extremely apparent at all frequencies, which Right channel showing a lot of distortion "grass", while Left is indeed very clean when comparing against other SE DACs I have tested.​


Conclusions
I finish this review feeling kind of exhausted. Measuring three products supposed to fill the same task, in addition to one acting as a DAC, was indeed quite time-consuming. Was it worth it? I am asking myself, as I already hear some questioning the relevance of the review... "Digital is digital", as such, all S/PDIF interfaces should give you the exact same performance. Well, yes, you are right: they should. Yet, I have already observed measured variations between other similar products, mostly audibly insignificant, but sometimes very noticeable (Frequency response and Jitter among others). With these S.M.S.L digital interfaces, there is nothing to argue any further. They all did a great job feeding a DAC with a 100% transparent digital signal. How boring it was to observe the same numbers again and again over dozens of runs... and very satisfying in the other hand, to confirm such a cohesive performance!

Back to the products: To me, the PO100 is the real bargain here. At 39$, it is way better built than its competitors. It also comes with stable USB drivers and USB-C instead of Micro-USB, which I have seen more often at this price point. As I personally consider both I2S and MQA to be useless, I would give it my highest recommendation. The PO100 PRO, while it showed no benefits for the use of "next-gen" XMOS chip, could make sense for those looking for better versatility and connectivity. As I like the format with all connectors on the same side, I will keep it for myself for measurements in the future.

At last, the PO100 AK... Well, let put it that way: Being 20$ more expensive, I see zero reason to choose this one over the PO100 PRO, if to be used as an interface only. As a DAC, though, I am really puzzled when thinking about giving it any appreciation. Yes, for 89$, you probably think to get some "transparent enough" D/A converter. Nevertheless, I just cannot ignore all the issues and dissimilarities I measured. Any audio gear should, at the very minimum, give the same performance between both channels, whatever performance that is. On top of that, the truncated frequency response is hardly forgivable. There has been a serious lack of care in design here (or maybe in quality control?) that is not acceptable, even for such a cheap DAC as this one.

Flanker rating:
PO100 / PO100 PRO: State Of The Art
PO100 AK DAC: Meh (finally Competent, after
re-measuring)
 
Last edited:

Tangband

Major Contributor
Joined
Sep 3, 2019
Messages
2,994
Likes
2,818
Location
Sweden
Thank for this extended review !

Here is the jitter comparison with toslink output between Douk U2 and SMSL PO100 pro ( Vintageflankers measurements )
SMSL PO100 pro on the upper picture.
721656ED-E2F8-415D-9DF4-B9D1E8A0F320.png
14B901B0-41AC-4C5F-8C68-241268CF0041.png
 
Last edited:

tonimccloud

Member
Joined
Jul 23, 2021
Messages
24
Likes
11
Great review! I've tried to purchase the original po100 some weeks before the release of the new ones...it was impossible. Although I don't need i2s and mqa, I bought the po100 pro for twice the price. It works like a charm with Windows and PlayStation 5
 
OP
VintageFlanker

VintageFlanker

Master Contributor
Forum Donor
Reviewer
Joined
Sep 20, 2018
Messages
5,105
Likes
20,437
Location
Paris
Here is the jitter comparison with toslink output between Douk U2 and SMSL PO100 pro ( Vintageflankers measurements )
Fortunately, that is not an apples to apples comparaison at all.;) One is done using a Matrix Mini-i Pro 3, the other through a Topping E70. In addition, this was done with an older version of Multitone, using different parameters and amplitude. There have been quite a few updates since!

I still have the Douk U2 on hands, so I may relaunch the test with the exact same conditions later.;)
 

Blumlein 88

Grand Contributor
Forum Donor
Joined
Feb 23, 2016
Messages
21,212
Likes
38,572
Well, I purchased a Douk audio unit last month. If I had waited I could have saved just a few bucks. Both are fine for my needs however. Thanks for the testing.
 

MacCali

Major Contributor
Joined
Dec 21, 2020
Messages
1,159
Likes
560
Thanks for the review, think I will buy this to replace my schitt eitr. I only paid a 100 when it was discontinued, plus it seems more convenient I can slap it onto my PC and Primo without much of a headache and have more digital outputs.

Confused though, amazon has the pro listed a dac.. it's a ddc, right? Only the AK has a dac.
 

pseudoid

Master Contributor
Forum Donor
Joined
Mar 23, 2021
Messages
5,418
Likes
3,774
Location
33.6 -117.9
At last, the PO100 AK... Well, let put it that way: Being 20$ more expensive, I see zero reason to choose this one over the PO100 PRO, if to be used as an interface only. As a DAC, though, I am really puzzled when thinking about giving it any appreciation. Yes, for 89$, you probably think to get some "transparent enough" D/A converter. Nevertheless, I just cannot ignore all the issues and dissimilarities I measured. Any audio gear should, at the very minimum, give the same performance between both channels, whatever performance that is. On top of that, the truncated frequency response is hardly forgivable. There has been a serious lack of care in design here (or maybe in quality control?) that is not acceptable, even for such a cheap DAC as this one.
Thank you for going through all the 'blood-sweat-and-tears'.
3 words :: You own it!:eek:
Hope your 2023 audio adventures find a use for that PO100 AK! ;)
 

MC_RME

Addicted to Fun and Learning
Technical Expert
Audio Company
Joined
May 15, 2019
Messages
899
Likes
3,679
The digital tests could be made in a different way, maybe more easy and even more accurate.

1. Generate a 1 kHz 24 bit ditherd sine, send it out via USB to SPDIF. Use one of your ADI-2s to receive and record that signal. Analyze the recording (or do it all in realtime with Multitone). The result should be a FFT of a 1 kHz sine full scale with a horizontally smooth and linear noise floor at about -180 dBFS, and nothing else. Any kind of bit mangling would show artefacts here.

2. Use DeltaWave to compare the original file (the played sine) with the recorded file. They should cancel 100%, proving bit accuracy.

3. In case you have any RME interface other than ADI-2 Pro/DAC you can use DIGICheck to see the Channel Status content of the DUT's SPDIF output, that way verify if that channel status includes wrong information (copy protection, bit length, sample rate, channel number, emphasis etc). Unfortunately this is a DIGCheck feature that due to technical reasons is not supported by the ADIs (they instead show Professional or Consumer status and Emphasis of the incoming signal directly on screen).

4. You could have used Bit Test to send out via your DUTs into the ADIs.

Just brainstorming...

Regards
Matthias Carstens
RME
 

AndreaT

Addicted to Fun and Learning
Forum Donor
Joined
Jul 19, 2020
Messages
617
Likes
1,197
Location
Commonwealth of Massachusetts
Excellent review. It shows there is no advantage to buy the model with the DAC due to its poor high audio frequency response from the the RCA analog outputs. The USB to S/PDIF transfer is impeccably done.
 

The Capstan

Member
Joined
May 4, 2020
Messages
65
Likes
70
Thanks VintageFlanker for this extensive review. I still think the Topping D10s is a solid choice if you need both Spdif/coax bridging and analogue out in a bit more solid enclosure. Also, Topping as a brand shows a more consistent quality throughout its product line, starting from its cheaper side, whereas SMSL here shows its limits.

On a side note, I cannot agree more on the “I personally consider both I2S and MQA to be useless” statement, especially for the MQA part. ;-)
 

phoenixdogfan

Major Contributor
Forum Donor
Joined
Nov 6, 2018
Messages
3,395
Likes
5,408
Location
Nashville
Thanks great review, VF. You have discovered an ultra cheap, completely transparent usb to spdif converter in tthe SMSL PO100. I'll probably pick up one or two b/c you never know when you might need one. The DAC unit is outdone handily by the Topping D10S which only costs $20 more on Amazon.
 

restorer-john

Grand Contributor
Joined
Mar 1, 2018
Messages
12,964
Likes
39,745
Location
Gold Coast, Queensland, Australia
Any audio gear should, at the very minimum, give the same performance between both channels, whatever performance that is. On top of that, the truncated frequency response is hardly forgivable. There has been a serious lack of care in design here...

These are the key takeways IMO.

Well done with your reviews!
 

MCH

Major Contributor
Joined
Apr 10, 2021
Messages
2,743
Likes
2,382
Thank you flanker, i like your comparative reviews, we kind of need them as Amir does not do them anymore.
This is a clear example of the smallest and cheaper of the family being the worthiest, and what does smsl about it? To discontinue it! Smart people :D
On a serious note, what would make a killer of these small converters is if they could be seen by the computer as a 4channel device (2coax+2toslink) a la digiface. Go for it smsl!!
 
Top Bottom