S.M.S.L PO100, PO100 PRO & PO100 AK Measurements
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.
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.
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.
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.
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.
- 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.
As a reference/performance target, I use a Topping E70, through USB input, balanced out at full voltage :
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
Noise Level
Dynamic Range
THD + Noise
Intermodulation Distortion
Crosstalk
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...
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
PO100 PRO
PO100 AK
(48kHz, 1-24kHz bandwidth, 16 averages, 262K FFT)
PO100
PO100 PRO
PO100 AK
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...
But now, it is time for something more interesting, we have a tiny, good-looking DAC to measure...
PO100 AK - DAC Measurements
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:
www.audiosciencereview.com
These are the initial measurements of the DAC:
S.M.S.L PO100 AK - Measurements / Round 2 (DAC)
S.M.S.L PO100 AK - Measurements / Round 2 Hi folks, This is an update over my previous measurements of the S.M.S.L PO100 family. I will focus precisely on the PO100 AK, which not only is an USB to S/PDIF converter (as are the PO100 and PO100 PRO) but also a budget DAC, that claims to perform...
www.audiosciencereview.com
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
Frequency response
| 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
| 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
| Left | Right |
Dynamic range, dB | +117.7 | +116.5 |
Dynamic range (A-weighted), dB | +117.6 | +116.1 |
Intermodulation distortion
| Left | Right |
IMD + Noise, % | 0.00076 | 0.00081 |
IMD + Noise (A-weighted), % | 0.00038 | 0.00044 |
Stereo crosstalk
| 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)
| 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?
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)
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)
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$, you probably think to get some "transparent enough" D/A converter. Nevertheless, I just cannot ignore all the issues and dissimilarities I measured. Any audio gear should, at the very minimum, give the same performance between both channels, whatever performance that is. On top of that, the truncated frequency response is hardly forgivable. There has been a serious lack of care in design here (or maybe in quality control?) that is not acceptable, even for such a cheap DAC as this one.
Back to the products: To me, the PO100 is the real bargain here. At 39$, 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)
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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!
