S.M.S.L SU-6 DAC: Closer Examination

I had just finished testing the TOPPING E30 II/L30 II stack, so the SMSL SU-6 does feel like it is targeting the same compact desktop use case with its relatively small form factor. The SU-6 is longer than it is deeper though, measuring in at 140 x 105 x 28 mm, so you will have to carve out more horizontal room here. It also weighs a whopping 350 g making it one of the denser DACs in its tier, but that is all due to the thick CNC machined aluminium alloy construction as opposed to ABS plastic, for example. The increased mass also makes the SMSL SU-6 quite stable on the desk and less prone to move around with attached cables, which was an issue with the JDS Labs Atom DAC+. I also previously mentioned how the SMSL SU-6 comes in black or silver versions, these are simply anodized colors on the aluminium base that gets a sandblasted matte finish. It feels cool to the touch but can be spotty with fingerprints which are easily wiped off. The Hi-Res Audio badge is part of the case itself and the lack of an MQA sticker is because there is no on-device MQA decoding support here, for better or for worse. I am on the former side given MQA certification would have added to the cost, and it doesn't make much sense in the more value-oriented market, but potential customers who swear by MQA need to be aware of this. On the front is the SMSL logo and product name, along with a glass panel that has an integrated display underneath. To the right of the display is the IR receiver port you should aim the remote at, and a capacitive button to work through the onboard menu.


The back side is where all connectivity options are found, including input and output options alike, in addition to certification logos. The SMSL SU-6 only offers single-ended RCA for output, either as a preamp to active speakers, for example, or to amplifiers such as the SH-6 itself. No interconnect cables are provided with the product, so you need to get your own set for the amp you pair this with—unless you purchase the SH-6/SU-6 stack that comes with free RCA interconnect cables. I would have liked to see dust covers provided on the various connectors as applicable, since it is likely you will only use one set of each at a given time. There is also no clear marking of input vs. output channels here so it can be potentially confusing to first-time users who do not read the manual or are not as familiar with the workings of a dedicated DAC. For the input side the SMSL SU-6 is fairly generous, with support for coaxial and optical inputs on top of the expected USB Type-C (thankfully not Type-B) input the provided cable works with. Then there's the Bluetooth input the antenna screws into, which will be handy for those simply wanting to stream music from their phones to a set of headphones or speakers. Rounding off the connectors is the 2-prong AC mains power, and I appreciate the large on/off switch on the side.


There isn't much to see on the bottom, with four small hemispherical rubber pads lifting the SMSL SU-6 up on your desk and preventing scratches to the metal case. These also minimize slippage on the desk, the weight helps too. After all testing was done, I attempted to disassemble the DAC for a close internal look. Things started simply enough with the four tiny hex head screws at the corners following which you can remove the bottom aluminium panel to also get a better idea at the case panel thickness throughout. Revealed is an internal plastic shield, complete with plastic push-pin screws to isolate the power section from the rest, containing a low noise switching power supply inside. There are more screws on the back of the PCB, but that's about all you can do here since the various connectors are soldered in place.

Thankfully, SMSL does help here by providing some photos of the PCB from the other side that also call out the various components of interest. We see the use of an ESS Sabre ES9038Q2M 32-bit low-power stereo DAC that's good for mobile/smaller-size desktop applications. I have used other DACs employing this very chipset in the past to very satisfying results. We also see the 2nd-gen XMOS U11690C20, ,an XMOS XU216 USB bridge with the xCORE 32-bit 8-core microcontroller that has been used successfully for USB audio Class 2 implementations. It's a step up from the XU208 you see in more expensive DAC units too, and can pass up to 32-bit, 768 kHz PCM playback to the DAC from the USB input, in addition to DSD64 to DSD512 native playback support and/or DSD64 to DSD256 DoP playback. The optical and coaxial inputs can do up to 24-bit, 192 kHz PCM playback. SMSL also boasts the use of four Texas Instruments OPA1612 op-amps inside, which also are not typically seen in such smaller/more budget-friendly units. There is also a discrete USB clock to reduce jitter as well as an unnamed Qualcomm "latest Bluetooth chip" which is likely a QCC5xxx series SoC for the Bluetooth connectivity itself. So far I am quite impressed with the hardware provided, all coming together for even more impressive numbers, be it the THD+N of <0.0001%, SNR of 125 dB, and an extremely flat neutral response vouching an uncolored sound signature from the single-ended RCA output of 2.1 Vrms with an output impedance of <10 Ω. This is a clear step up from the TOPPING E30 II DAC, for those curious.