[Impression] S.M.S.L M3 Mini USB Powered Audio Decoder with Headphone Amplifier
Apr 5, 2017 at 1:42 PM Thread Starter Post #1 of 1


1000+ Head-Fier
Oct 20, 2013
I happened to have got given this by SMSL free of charge as they liked my review of the S.M.S.L SD-793II that I did some time ago. It was a 2nd hand item and was probably returned to the seller as it has an obvious sign of damage under the amplifier. A scratch but that is all. It hasn’t changed the function of the device so it is still fair to do a review.

Really solid construction. I don’t think anything about the build needs to be any better for the price you pay.

Powered by 5V USB.

Has 3 different inputs to convert digital audio. (Coaxial, Optical and USB)

Again, like the S.M.S.L SD-793II, it looks and feels quite a bit more pricey than it is.

Doesn’t go particularly loud compared to the S.M.S.L SD-793II and especially the FiiO E10. Considering the E10 just uses 1 USB socket to power it, it is a little disappointing that this is so much quieter even though it should be capable of using more power.

Just one button to operate everything. It has to be pushed and held to turn on or off.

(Update 6/5/17)
Whenever the sample rate changes with the coaxial or optical input, you often miss a fraction of a second of what you have just played.

Powered by USB. While I said this was an advantage, it also isn’t. I find powering things by USB all to often allows noisy interference to be heard. This unfortunately is the case with many cheap 5V USB power supplies.

Quiet PC background noise while using the digital USB input. This may be a problem with my PC, but when you pause what you are listening to, you can hear the internal parts of the PC working away. It is all extremely quiet but this doesn’t happen using the optical input.

Rather bright white lights on the front to indicate the power, input and sample rate. This may not sound like much of an issue but again, I’ll explain in more detail about it later in the review.

Like on my other review, there look to be more disadvantages. But it is the same again, most of the disadvantages are only really minor issues.

The Front:

I have it on a small shelf and it looks pretty neat. It is really solidly built and unlike the SD-793II, I think the volume control is really solid. I’ve seen several people say it is made of plastic. Well that isn’t true. It may not look like it, but it is metal. You can tell by the sound of it when you tap on it. The dial also feels nicer to turn than on the other amplifier. When your room is cold and it hasn’t been on, the dial also feels cold to the touch like metal does. The dial also feels firmer and less likely to get knocked too far suddenly. It has also got nice grooves all the way round it which make it feel nice to turn. The headphone socket is again very solid and clicks into place really well. I leave a 6.3mm adapter in the whole time. Even when you pull the 3.5mm jack out, the adapter always stays in place.

What I don’t like is that there is only one button that does everything. You have to press it pretty firmly and as the amplifier is so light weight, you end up moving it unless you hold it still while pressing the button. To chance inputs, you just press the button quickly and it will go from input 1 which is USB, then to 2 which is optical, then 3 which is coaxial then back to 1 again. The annoying thing is just that you must press it twice to get to where you want a lot of the time. You also need to need to hold the power button for around a second to turn it on or off. The other issue I have is to do with the lights which I will explain more in the pictures below.

This is what the lights are like when it is in standby. I find this a bit strange really. That light is bigger and possibly brighter and certainly more obvious than the others when it is on. It just looks strange that when it gets turned off, a big bright light turns on. I do have a small room but when it is dark, this actually lights my walls up slightly! Even if I leave it on, which I do pretty much the whole time, I still find the other lights too bright. It isn’t very comfortable on the eyes while watching a film in the dark if you have these bright white lights on all the time. I actually put some strips of green electrical tape over them to make them a lot less obvious and I’m fine with it now. Some people may actually like to have bright lights, but I don’t. It will be fine for day time or bright room use, but as I use it late in the evening, it was a bit of a pain until I did this. I just don’t think white is a good colour for lights on an amplifier. I tend to prefer red, green blue as that seems to be more common.

Another issue that I mentioned was a disadvantage was the sample rate lights not being accurate. This maybe could be my PC at fault again but for some reason, when I play a track that has a sample rate of just over 88kHz, it just has the lowest sample rate light lit which is 44kHz. When I play the same track on my FiiO X3 through the coaxial output, then the 88kHz light will light up. What I find really strange though is when I open a program such as a game I often play on or Kodi, the sample rate goes up to 48kHz on the M3. But on my PC when using USB, it won’t go higher than that until I shut my PC down! Then for some bizarre reason, the 88khz light comes on when it is receiving no audio. With the other 2 inputs, the lights that tell you the sample rate turn off when you switch your device off. With USB, it doesn’t do this so maybe it is related to the fact it provides power. But even so, it shouldn’t have its highest sample rate showing when it is turned off.

When I watch Blu-ray disks with my player through coaxial, it works perfectly here although I still haven’t seen it go any higher than 88kHz but then I don’t really know much about what stuff is that high.

This picture may make it a bit more clear how bright the lights are. Something that maybe could be improved is something to stop the light from one travelling to another when it isn’t even on. You can’t see it in the picture but when just one light is on in the dark, you can see several of the others glow slightly. To me it would be better if this didn’t happen. If they were not so bright, it probably wouldn’t happen.

Another picture of the Front:

From the Top:

There isn’t really much to see here. It feels more expensive that it looks.

The Bottom:

This is where the obvious scratch is. They clearly won’t all be sold like this! The feet on this are soft but I think the feet on the SD-793II were better. They were more like rubber and they kept it still. These are more like firm foam and it slips quite easily as it is very light. A bit annoying when you have to press and hold the power switch to turn it on or off.

The Back:

For the price of this, I think the range of inputs that is offers is very good indeed. If it wasn’t for the fact that both my TV tuner and Blu-ray player both have coaxial outputs, I would probably be using all 3 of these inputs very often. If you are using input 1, as it is USB, you don’t need anything to be plugged into the DC input. And also, if your PC permanently feeds power through the USB cable even when it is off, you won’t even need to have anything in the DC socket when using the other inputs. I just have found that for some reason, if I do power it by that too with my Anker power supply, it helps reduce the quiet interference noises I get from my PC. At the moment, I’m using all the ports other than the optical one. I just can’t get optical to work properly with Ubuntu as I mentioned earlier. I use the phono out with a splitter and adapter. One going to my Pioneer A-209R integrated amplifier to power some bookshelf speakers that I use as my PC audio and the other goes to a 3.5mm jack which I use to go to the input of my FiiO E11 or A3 headphone amplifier. If I’m wanting more volume with my headphones or some extra bass, that is what I use.

At an Angle:

Something interesting about the volume control is that you can see it has a hole in it. There is a tiny bolt inside that you can unto with a small allen key This somehow spoils the look of it a little bit but it holds it in place really well. It doesn’t wobble as much as the one on the SD-793II.

Package content:

I expect that usually, a user manual will be included but mine didn’t come with one. It did however come with 2 USB cables. One micro to micro. I assume this will be so you can use your phone to be the source. I think a phone may struggle to power it though. But you could also use a USB power bank and then power it by that. This is one reason why being powered by USB can be very handy. The other long cable is just a standard USB to micro USB. What is a nice surprise is that it includes a 3.5mm to 6.3mm adapter. But I already have about 5 of these things not in use so it is just another to add to the collection.

SD-793II and M3 comparison:

I still actually think that the SD-793II looks better. All the metal on it has a nicer looking finish on it. The M3 has more of a matt finish everywhere. But when you hold it, The M3 certainly feels more well made. I think the metal will be thicker too.

Size comparison:

I have a whole load of FiiO amplifiers and DACs. This picture shows the E11, A3, X3, D03K, E5, E10 and the 2 SMSL ones. The M3 is bigger than any by FiiO. I still think that the build quality of the E10 and A3 is just as good as the M3 though.

About the sound and inputs:
This amplifier can comfortably drive 32 ohm headphones like my AKG K550s and Audio Technica ATH-AD700s but It probably doesn’t get the most out of my AKG K702’s. They are 64 ohm headphones and are quite a bit harder to drive. I usually listen to them with the dial turned half way up. This is reasonably loud, but not as loud as the SD-793II with the dial at this position and nowhere near the FiiO E10. The other strange thing is that turning the dial to full only makes a small difference. But this will just be my headphones. I’m sure this amplifier will be good with others. It is fine with my K550s and AD700s. The sound quality is excellent for the price though. I’d say it is a little better than the SD-793II but not by that much. But I’d say it is worth the price difference because of the improvements it has even if it isn’t as good in 1 or 2 ways. I don’t think this amplifier will be a massive improvement in sound quality if you already have a very good sound card but if you are wanting to convert 3 different digital inputs to one output, then this works out perfectly. If you need more volume over a standard PC sound card, this will also do the job well too.

Something I like about this amplifier compared to the SD-793II is that it doesn't click at all when it receives or looses signal. With the SD-793II, even when I tried it with a TV optical output in another room, any time you turned the TV on or off, paused a video, skipped forwards or backwards, changed channel or any thing like that, it just made a loud click the whole time. It was fine if you left everything alone though at leased. It may not have missed out any audio, but it was very annoying. The M3 is silent and never clicks.

I have figured out though that Ubuntu doesn't work very well with the optical output on my computers. You miss a fraction of a second out every time you switch application. Eg, if someone on Skype comes online if you have been playing sound from a different application, you hear the 2nd half of the notification sound as it takes the PC time to detect the signal. I don't believe windows will have this issue. Coaxial with my Blu-ray player and USB with my PC pick up everything fine.

(Update 6/5/16)
In the paragraph above, I wasn't right about Ubuntu being the problem. I now think it is actually the M3 at fault for the delay between different applications. For example, I tested this using the my E10. The E10 uses USB for the input. It also had a digital coaxial output. I then put a coaxial cable from my E10 to the coaxial input of my M3. And now, it seems that whenever the sample rate changes, this is where it chops off the first half second or so of what you play. I know the M3 is at fault now as when I plug my headphones into the E10, there is nothing chopped off. To test the optical output too, I used my HDMI audio extractor and plugged that into my PC HDMI port. With the line out on this, there was no delay, but with the optical output plugged into my M3, there was the same problem whenever the sample rate changed. This is a pretty big problem. So now, I always am using the USB input on the M3 for my PC audio as that seems to not have any issues with skipping the start of your audio when the sample rate changes. Luckily, I have tried the optical and coaxial inputs on the M3 with my Blu-ray player and TV tuner and it seems fine with that. This will probably be because the sample rate is virtually always the same though.

Another issue I have with this amplifier is that it is powered by USB. This is useful that you can actually power it by input 1 or the separate USB DC input. So you could power it by just a laptop with one cable if you are using the digital USB input. It would be better if they included their own power supply that was 9v or 12v like the old one so it could more easily have more power and avoid the interference you get with cheap power supplies. I spent ages trying to find a suitable power supply that didn't introduce a load of horrid noise in the background. The power supply with the SD-793II made no audible noise at all and it was really clean with both the inputs. With this, I tried many and I eventually went for a USB charger by Anker and that is nice and clean. It it just so hard to find a decent one and USB power supplies are not really designed to power audio products and that is why I wish it came with its own supply!

Product description from (www.shenzhenaudio.com):
SMSL M3 mini multi-function all-in-one DAC/Headphone Amp, has excellent performance, flexible operation mode, intuitive display, delicate appearance and rich input/output interface. Digital input : USB, Optical fiber and Coaxial digital input.

Output: RCA analog output and 6.35 headphone jack. It supports OTG USB and computer USB, which can make charging more easy no matter you are in the office or in bussiness travel.

M3 can be directly powered by computer,Android tablet PC and android mobile phone(This function is not avaliable for Apple Ipad or iphone).With purified power circuit
Externally enhanded power input jack using DC 5V,Maximum power is 1.5W,Users can connect with power bank to work this product which can generate better sound quality.XIAOMI 10000ma power bank can work up to 20H with M3.
24 bit asynchronous USB input, 24bit/ 192KHZ advanced decoding chip is CS4398
Big power headphone amplifier almost can be compatible with all of Hi-Fi headphone.
Industrial design input and full frequency sampling rate is clear to see from front panel ;
High quality aluminum alloy shell, solid aluminum buttons and knobs.
The high parameters and highly integrated product will occupy it’s market for high cost performance.

It can get power supply by connecting computer, android tablet, the android mobile phone directly( not including ipad and iphone) with built-in power purification circuit.
External strengthen power input interface using DC5V power supply with, maximum power 1.5 W, can use charging power supply makes sound more good treasure.
Having 24 bit / 96 KHZ asynchronous USB input, 24 bit / 192 KHZ ,advanced CS4398 DAC chip and high-power headphone amplifier, it can be compatible with almost all enthusiast headphones.
The industrial grade design and full frequency sampling rate are clear at a glance.
The aluminum alloy shell, solid aluminum buttons and knobs, the high- quality parameters and highly integration , which all helped M3 to occupy the market.

Don't need to install the driver. Please set the output to 24bit to fit the foobar 2000 music player.

Output levels:1.9Vrms
Dynamic Range:112dB
CHANNEL separation:105dB
Sample rate:
Amp output power:
32Ω 108mW @THD=0.1%
64Ω 85mW @THD=0.1%
150Ω 49mW @THD=0.001%
300Ω 24mW @THD=0.001%

As is often the case with many Chinese companies that are not very well known, the English translation is pretty poor but it is easy enough to understand.

Even if I had bought this at the price it is selling on amazon.co.uk (£69.99), I think it will have been worth it. It does have issues but none are enough to make me want to try and get anything better. It works out extremely good value if you know you will be using every feature and input it has.

I noticed there was a thread that was created not that long ago saying that there had hardly been anything about this amplifier on Head-fi and since I did a review on another one of their products, I thought I may as well do one on this amplifier.

(Update 6/5/17)
Now I have worked out the issue with the optical and coaxial input delays when the sample rate changes, I don't think it would be worth the full price it sells for. If you use a device that is constantly changing the sample rate, this can get very annoying indeed. Lets hope SMSL can prevent this happening with their other products.
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