REVIEW: SMSL A6 integrated amplifier - Part I: Overview and Subjective Listening (and briefly about USB cables)

SMSL A6 at home in my living room system with Tannoy Mercury Mx2 speakers. Doug MacLeod's Break The Chain (2017, Reference Recordings 24/176.4 downsampled to 88.2kHz, DR16) playing over Logitech Media Server.

For many years, my father's audio system consisted of various CD players, a Sony turntable and vintage pre-amplifiers. This then fed a tube pre-amp which then sent the signal to either a tube-based Onyx SP3 Melody amplifier or vintage solid state Pioneer amplifier to feed his Klipsch Forte speakers which have been cleaned and refurbished with new crossover parts over the years.

In the last 5 years, I've supplemented his system with various DACs for the CD player, and most recently got him a streaming connection with my Logitech Media Server based out of my home server using a Logitech/Squeezebox Touch.

This set-up sounds very good. The classic Klipsch speakers really do throw up a fantastic soundstage, have quite a smooth sonic signature (though a little mellow for my taste), is extremely sensitive, thus easily powered by low-wattage amps.

He has gradually transitioned to almost exclusively digital streaming, finding the convenience indispensable compared to spinning disks (whether of the polycarbonate or vinyl variety). As much as the tube and large integrated amps sound great, over time some of those components have needed maintenance and I figured it would be nice for him to try out something much simpler than manually turning on/off multiple devices every time he wants to hear good sounding audio. Thus, the purchase of the SMSL A6 integrated DAC/amp.

After the positive experience with the company's iDEA DAC a few months back, I figured I'll give this a try as it seems to fit his needs (plus Amazon has its usual 30-day easy return policy). At ~US$450 it's certainly not expensive for the features listed and with a phono input and separate analogue line in (for CD), he can hook up his whole system without fuss.

I. Physical Characteristics

Let's have a peek at the device:

The image above to the left is the box contents with the integrated amp, manual (surprisingly detailed compared to many other items from Asia), a short IEC power cable, generic USB cable, driver CD, and of course the remote. I show a close-up of the remote to the right. The remote feels quite good in the hand - metal construction with good weight, rubberized action on the buttons.

It seems that this remote must be a "universal" remote of sorts for SMSL products. The "A", "B", and "C" buttons seem to select different devices with the "A" assigned to the integrated amp. If you seem to have trouble controlling the device, make sure you press the "A" button first just in case someone had pressed B or C.

The prominent power button brings the device out of sleep when plugged in. The multidirectional ring allows volume control (up & down) and the various inputs (left & right). The center button toggles between various settings (including the color of the main text on the LCD screen - the "white" setting looks good). The button to the right of "A" with the arrow pointing down into a round icon is the input selection toggling between USB, the various S/PDIF options, analogue CD input and PHONO. "EQ" allows various settings like DIRECT, SDB, and TONE. DIRECT is without processing, SDB refers to "SMSL Dynamic Bass" - their bass boost system, and TONE allows manual +/-9dB gain in bass and treble. As you may suspect, unless specified otherwise, I stuck with DIRECT.

As an IR remote, it has to be line-of-sight +/-30-degrees from mid-line and SMSL recommends within 7m distance. As usual, I'd probably program the device into a learning universal remote if I were to keep it in my system.

Front panel is basic and non-flashy (good!). The centrally located LCD screen which can be seen in use above measures 1"x 1" which is small from a distance but the input selected (eg. "OPTI" for optical) is displayed with a larger font. You can change the color of the main text if you want (white, red, green, blue, yellow, purple). The LCD brightness isn't high which may make visibility more difficult in a bright room but for nighttime listening the setting is just fine and absolutely unobtrusive especially with a darker color like blue for text color.

It has 2 knobs - the left one allows you to toggle between menu items and settings. The right knob is the on/off switch when pushed down for a few seconds. When it's on, a quick click down mutes the device and rotating the knob acts as volume control.

You can also see the headphone output on the front. As with most devices, it will detect the presence of headphones in the socket and mute the amp while in use.

Here's the back. Standard IEC power connector. Right / left binding post output to the speakers - I just used locking banana plugs. A collection of 3 digital inputs - asynchronous USB, S/PDIF TosLink and coaxial. Then there are a series of analogue RCA's - line level output from the DAC if you want to use your own amplifiers, analogue (CD) input, then analogue phono input with accompanying ground lug to the far left.

No fancy features like network input, WiFi or Bluetooth. It's designed as a no nonsense integrated amplifier and quality DAC.

I found the metal enclosure sturdy and the device has a solid feel to it. It weighs in at less than 5 lbs which means it's not going to strain any actual bookshelf you might want to put it on. Notice that the exterior has a matte black consistency to it. While I prefer a bushed metal look, at least it's not highly reflective but it can be harder to keep clean when fine dust or oily fingerprints get on the surface.

As you can see in the image up top with the Logitech Touch sitting on top of it, it's quite a compact device measuring ~8.5" x 7.9" x 1.75" (21.5 x 20 x 4.5 cm). 

II. Features & Internals

Like with the iDEA DAC, SMSL isn't shy about telling us what's in this device on their web page. I see this as a good thing as a "more objective" audiophile. Although just knowing the components themselves will not tell us how well the device is implemented, it does give us an idea of expected capabilities and potential quality.

On the DAC side, they're using the Asahi Kasei AK4452 converter, a recent ~2015 "Premium DAC" with the capability of receiving up to 768kHz PCM and DSD256. Although there are no filter settings with the A6, I see that the chip itself does have a few options available to choose from. My assumption is that the default filter is a sharp roll-off settings which the datasheet describes as performed in 32-bits with 8x oversampling (we'll have a look when I run some measurements).

Although the official DAC chip specs say DSD256 "input maximum", SMSL has allowed DSD512 input through the CMedia CM6632A asynchronous USB2.0 audio interface. Like with the iDEA, whether DSD512 is an undocumented setting or if there is some downsampling going on, I'm not sure. In any event, I have long used the CM6631A USB to S/PDIF interface since 2013. Given how well jitter was controlled back then with the older iteration of the silicon, I anticipate that timing will not be an issue here either.

For the headphone side, the Maxim MAX9722A amplifier is used here. The datasheet describes this as capable of ~130mW into 32-ohms <0.02%THD+N at 1kHz. Looking at the graphs, it drops to about 55mW into 16-ohms <0.1dB THD+N. They call it "DirectDrive" - no DC-blocking capacitors necessary. Clearly not the most powerful headphone amp, but probably adequate for most users.

I've got my 1MORE Quad Driver headphones plugged in playing Imagine Dragons' Night Visions. Notice on the front screen that it's using the "OPTIcal" input, headphone volume at 14 (out of 40), PCM 44.1kHz input. My digital camera accentuated the brightness of the LCD screen. In use, the background is clearly dimmer than the picture.

Finally, as advertised on the front, this device uses an ICEpower amplifier. ICEpower 50ASX2 Class D amplifier to be exact. ICEpower as an OEM provides amplifier boards for many companies and is 100% owned by Bang & Olufsen since 2008. This specific device is rated as 2x50W into 4-ohms, 1% THD+N in the audible spectrum both channels driven. At 8-ohms, it's rated at 25W with 1% THD+N.

As you're likely already aware, Class D "switching" amplifiers are much more efficient than typical Class A and A/B amps. They use less total power for the same output and dissipates much less heat. In standby mode, the A6 uses <4W. Turned one for more than an hour, the A6 case will warm up slightly, but stays notably cooler than my ASUS XONAR Essence One desktop DAC. If you examine the enclosure, there are no cooling vents anywhere.

III. Subjective Sound Quality

As usual, I will run this device through a test bench in the weeks ahead.

For now however, I can say that this device does work well and sounds very good. Since I bought it for my father, he was quite happy with the flexibility and ease of operation. Without fancy network operation or other complexities, you just plug in your devices and speakers, select your input and away you go with the convenience of the remote control. Plug in, press the "on" button, and he's ready to play in a couple of seconds (no long boot sequence like some devices these days!). My father likes the typical audiophile female vocals genre so music like Cai Qin's (蔡琴) Collection is right up his alley. No concerns at all matching the A6 with his classic Klipsch Forte speakers. They're efficient with a sensitivity of 98dB SPL/W at 1m, 8-ohms, so the 25W rating is just fine for listening in a moderate sized room. Excellent imaging with the front-and-center vocals. Backing instruments sounded clean. I know some people complain of Class D amps having a sharp "sheen" or adding a "glare" to the sound. Certainly with these speakers, to my ears, there was no problem with the pairing whatsoever... Although A/B'ing takes a few seconds switching cables, the sound is comparable to his Class A/B Onix SP3 integrated tube amp which was a lot more expensive a number of years back.

I must admit that although the Klipsch Forte speakers are fine for the mostly vocal and acoustic music my dad listens to, they seem lacking in treble extension for my taste. Note that this is subjective since I've never taken my measurement mic to his system and may be just a reflection of his room acoustics rather than the speakers. Nonetheless, I did enjoy the recently released live Paul Simon The Concert in Hyde Park (2017, 2 CDs, around DR10). I've always liked the sense of spaciousness of the Klipsch sound and a live recording like this really brought out the energy of the concert!

For a more familiar comparison, I took the SMSL A6 home and downstairs to my main listening room... As a size comparison, just have a look at how small this device is compared to my Emotiva XPA-1L monoblocks, Emotiva XSP-1 preamp, DAC and speakers sitting on top of the Technics SL-1200 turntable!

I hooked up the Raspberry Pi 3 Touch player via USB to the SMSL A6 input for a listen. The Raspberry Pi 3 had no issues detecting the A6 using piCorePlayer. As usual, select the proper USB input:

Subjectively, I'm sure it will come as no surprise that a modern Class D amp sounds good. What is noticeable of course is the fact that we are looking at a 22Wpc (into 8-ohms, 0.1% THD) amplifier here compared to my 250W (into 8-ohms, 0.1% THD) Emotiva XPA-1L monoblocks! Although the Paradigm Signature S8v3 speakers are reasonably efficient at ~92dB in room, when I run DSP room correction which applies a bit of attenuation, at 100% volume on the SMSL A6, the volume is loud but certainly not intolerable in my room of about 15' x 20' x 8' size. I have never pushed the XPA-1L monoblocks to 0dB on the preamp in actual listening; that would just be painfully loud and subject one to premature hearing loss!

Apart from the expected power limitation, the only thing I thought I noticed was a little more harshness in some of the compressed pop/rock music. For example, listening to the recent Coldplay & The Chainsmokers tune "Something Just Like This" (off Memories... Do Not Open, 2017, DR5), the vocal sibilance was a bit harsh compared to the monoblocks. Though I would not consider modern pop audiophile fare, I figured it was worth noting.

High quality recordings sounded great - Doug MacLeod's Break The Chain (2017, DR16) is a good example of a modern hi-res recording with great dynamic range, lots of detail and nuance for those into straight-up blues. The recording BTW was done by "Prof." Keith O. Johnson at Skywalker Sound with the CD release apparently still encoded as a HDCD (even in 2017). Great lyrics, performance and sound quality on the title track for example. Beautiful how the instruments just "hang" in the atmosphere enhanced by the natural sounding percussion section.

Something I liked about the A6's USB input is that even when switching between different sources, the USB connection remained intact from the perspective of the streamer. On some DACs like my TEAC UD-501, when I switch out of the USB input, the device will disconnect from the streamer or computer. Not so with the A6. I can switch between the different inputs while playing from USB and the streamer won't skip a beat.

The inclusion of a phono input makes this device also attractive for those who might also have a turntable in the system. I attached my Technics SL-1200M3D with Denon DL-110 HOMC cartridge into the phono input and playback sounded "full bodied" and very pleasant (remember, my opinion is that vinyl isn't capable of true high-resolution so I tend to accept the idiosyncrasies and enjoyment is good enough without needing to be too analytical with the sound extracted off the plastic grooves). An early pressing of The Beatles Abbey Road, Springsteen's Born To Run, and Daft Punk's Random Access Memories from a few years back served as familiar evaluation material. The RIAA compensation sounds good enough to me. Although not explicitly noted, you will need a step-up transformer for low-output moving coil cartridges. The manual did not provide any details on phono impedance matching so I assume it's expecting standard MM cartridges with characteristic output voltages ~3mV and 47k-ohm input impedance (and my Denon HOMC sounds great plugged into this).

IV. Impressions

Years ago, when I was in university, I used a Sony integrated amp which carried me through many years of college life. I imagine these days with music on computers, with streamers like the Pi 3 easily constructed for cheap, if I were a student with limited budget but want really good sound, a device like this would fit the bill. Pair this with passive (good but inexpensive) speakers like maybe ELAC, Wharfedale, Pioneer, Paradigm, Tannoy, PSB, KEF, Mission, etc. bookshelf models and the audio quality will more than likely be excellent. In fact, because I believe "good sound" is primarily a function of the speakers and room, the bang-for-the-buck is to save money with the DAC / amp / streamer side of things while putting more of the cash into your speakers. Given the size, I imagine the A6 would also be a good desktop computer audio workstation system with passive speakers functioning as a very feature-filled PCM/DSD DAC.

On the other hand, as I mentioned at the beginning of this post, the reason I ordered this device is for my father. Even though he has enjoyed hi-fi sound for years, there's something to be said for simplicity and convenience! I see it as "downsizing" but without really paying a terrible price with reduction in sound quality compared to what he's already using. Even better is that this device is much more efficient which keeps it cool in the summer, and saves a few dollars in energy costs (Class D is much more environmentally friendly, right?). So far, my dad thinks very highly of the convenience and sound - calling me a few times as I currently have the device for testing, wondering when he can have it back :-). Thus easily achieving the goals of the purchase in the first place.

Remember that there are quite a number of options out there when it comes to small integrated amplifiers like this with DAC functionality. For example, there are the inexpensive Onkyo A-9050 (75Wpc into 8-ohms, a little larger, US$350), NAD D3020 (30Wpc into 4-ohms, Bluetooth aptX, US$400), TEAC AI-301DA (same ICEpower 50ASX2 amplifier as the A6, US$400) and PS Audio Sprout (32Wpc into 8-ohms, US$500) around the same price range as this SMSL A6. Higher up in price we have the NAD D7050 (50Wpc into 4-ohms, network streaming, US$800), and the ELAC Element EA101EQ-G Integrated (US$700, 2.1 channels, 80Wpc into 4-ohms). Even higher up the price range, one could look at the beautiful Marantz HD-AMP1 (US$1100, 35Wpc 8-ohms, 2.1 channels), Peachtree nova150 (US$1800) and nova300 (US$2500). The Peachtree novas are using higher power versions of the B&O's ICEpower amps internally. Each device will have varying features like a remote control, number of digital inputs, Bluetooth, phono input for turntables, samplerate & DSD capability, headphone output quality, etc... Important to do some research to find the right features for your needs.

Since this is my first time writing about and testing a product like this, I figure it'll be interesting to take my time and explore a few of the functions to see how well a US$450 device like this in 2017 works objectively. Next up we'll have a look at the quality of the DAC output with the AKM AK4452. In the next few weeks, I think I'll also spend some time measuring and comparing the output of this Class D amplifier with other amps I have around here. Stay tuned...

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Did Digital Audio Review close off the comments section about a week and a half ago correlated with a series of questionable, if not a little paranoid articles about USB cables, power products, and even more words spilled on USB cables? I suspect those articles would have garnered quite a number of responses and many more reads if people were allowed to comment. As for the gist of that latter article, realize that objectivists typically seek to understand what devices can influence the sound the most. Speakers are much more complex and most will appreciate that it's not unusual to hear differences. Amplifiers can have their own sonic signature with variation in frequency response, harmonic distortions, clipping behaviour, ability to drive demanding loads, etc... This is why reviews can sound very plausible and typically not terribly controversial when it comes to things like speakers and amps. But USB cables??? 

Suppose a friend called me up after a hike in the woods describing how she saw a grizzly bear along the way (grizzlies of course live in this part of the world). That would certainly be very interesting and worth discussion. But what if she claimed that she saw Sasquatch/"Bigfoot" (also supposedly living in this region of the world) on Facebook? Would it not raise a few eyebrows among friends? Create more chatter? Even suggestions that she may have been mistaking a bear for the mythical creature? So too, unlikely claims made by typically purely subjectivist reviewers about audible benefits of expensive cables will tend to stir up more controversy. No surprise.

I'm happy to admit that jitter does happen - but inconsequential with any decent asynchronous DAC these days and standard length cables cannot affect the DAC's jitter performance anyway. I'm even happy to demonstrate what audible distortions sound like due to data corruption by a very poor cable. But where is there evidence that any expensive USB cable sounds better. Where is there even a logical explanation for alleged profound changes to tonal balance, apparent amplitude, soundstage differences reported by various reviews over the years? Digital transmission is well understood and brings with it various self-evident truths about what is and what is not possible. This is not only from a theoretical framework but also in real-life practice! If this were not so, how would we even be communicating with such reliability over the Internet? How can we be streaming lossless audio with such high quality (Darko uses TIDAL right?)? How could Netflix be streaming 4K video at 15-30Mbps with multichannel sound over thousands of miles, likely switching between optical and wired cabling without deterioration if we can't even get audio transmission right over a few feet using a USB cable (BTW, only 1.4Mbps lossless CD, 4.6Mbps 24/96, 9.2Mbps 24/192)!?

As for this beautiful nugget:

"But wait. If xxxxxxxx and yyyyyyy are on the opportunistic take, it follows that every USB cable manufacturer is a con merchant; that reviewers of their products are also shills; and every owner of an audiophile-grade USB cable has be duped proving that a fool and his money are soon parted. Hundreds of reviews and thousands of end user comments – all lies."

(Names removed to protect the "innocent".) Please, why so dramatic - "con merchant", "shills", "duped", "fools"? First, there's nothing wrong with taking opportunities. That's inherent in capitalism - go ahead and satisfy the demand and profit from it. I write this blog, I turn on AdSense, I make a few bucks if readers find the topic interesting and the ad catches their attention. The question is at what point does the taking of opportunities cross the line and become immoral? Pharmaceutical and nutritional supplement companies take advantage of opportunities to sell a product all the time even if benefits may be marginal or practically insignificant - at what point do marginal benefits become fraudulent claims? Dr. Oz promoted "miracle" pills; doesn't he still have a good sized following? How many millions (even billions) of people have strong faith-based allegiances to horoscopes, miracle healers, psychics, and countless spiritual organizations? Some individuals might be lying, some might be opportunists, some might be psychotic, some might truly find benefit in different ways. If you ask the "faithful", many will recall experiences which they believe "prove" their faith just as some in the world of audio have "heard" a $5000 USB cable sounds better to them than a $1000 one.

I'm certainly not saying that faith does not have a place in this world. I actually believe the subjective world is extremely important; but that's another broader discussion. However, when it comes to electronics, digital communication, and USB cables, the "hundreds of reviews and thousands of end user comments" are certainly NOT "all lies". Expressions of faith may be genuine, even if ultimately mistaken when the belief is explored under controlled conditions. And yes, IMO some out there are just liars, or complicitly "toe the party line" based on financial motives - let us not pretend to be naïve, as if it could be any other way in the face of the profit margins for selling "high end" wires!

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I just want to end this post with a shout out to Mitch Barnett (aka Mitchco on Computer Audiophile) for his hospitality last weekend when I went to visit him at his place at the beautiful Sunshine Coast (alas it wasn't particularly sunny that day)! It's great when the joys of a hobby develops into relationships with fellow "travelers" on this journey. Thanks for the beverage, sushi and discussion of topics far wider and deeper than just sound reproduction... :-)

I hope everyone is enjoying the music. Remember to listen to the MQA Blind Test and keep the survey results coming! Another month to go...

UPDATE (Aug 5, 2017): SMSL A6 Measurements - Part II - exploration of the DAC objective performance and a bit about the headphone output is now up.