The SU-6 is an updated model to the very popular SU-1 Digital Interface from Singxer. The SU-6 is more than 1.5x the price of the SU-1, but is still modestly priced for a high performance USB Digital Interface.
The burning question though for most people would be why the need for this product ? USB inputs on DACs are ubiquitous and having an off-board solution is practically speaking not required. Apart from the expense of an additional box, you also have to budget for an additional digital cable, rack space and other accessories like a power cord and footers.
My personal experience is that most DACs do benefit from being paired with high quality USB converters, often sounding significantly better compared to a direct connection to the DAC's USB input. In the case of the SU-6 (and also the SU-1 for that matter), it also brings I2S output to the table for compatible DACs.
The SU-6 is a compact metal black box, with three indicator lights on it's front panel. The rear panel reveals the flexibility of the SU-6, with a DC jack for it's supplied external power supply (you can use any 7.5 - 9 V DC power supply with a 3A current rating), a USB input, and no less than 7 digital outputs, and a word clock output. Not bad for a product that carries a three figure price tag.
The digital outputs consist of two SPDIF jacks (one coaxial and one BNC), AES / EBU, Toslink, and three I2S outputs (two HDMI sockets, and RJ-45). Since there is no industry standard for I2S, Singxer thoughtfully includes a bottom panel cutout with a variety of DIP switches to configure the I2S output. I did not get to test this, although I tried the SU-1's I2S output over HDMI with the Holo Spring and Denafrips Pontus DAC.
A word about the power supply - the SU-6 uses a 7.5 F (7.5 million uF) supercapacitor power supply, the supplied switched mode power supply is used to charge up the internal power supply.
The SU-6 utilises two Crystek CCHD low phase noise Femto second clocks. These clocks are contained in a metal enclosure for temperature stability.
All common sampling frequencies are supported, including the ability to handle 32 bit data. DSD sampling rates cover DSD 64, 128, 256 and 512. 32 bit data is only available over I2S as the SPDIF standard supports up to 24 bit data only.
The key differences between the SU-1 and SU-6 are set out below :-
Power Supply Onboard linear power supply SMPS + Ultracapacitor power supply
Femtoclocks One Two (Temperature controlled)
I2S HDMI HDMI and RJ45
DSD Support 64, 128 and 256 64, 128, 256, 512
Digital Outputs AES, 2 x SPDIF, 1 x I2S (HDMI) AES, 2 x SPDIF, Toslink, 3 x I2S (HDMI / RJ45)
Customised I2S Yes Yes
Power Switch Yes No
The proof of the pudding is in the eating. In the case of the SU-6, it offers a sweeter taste with less astringency and a fuller and more refined mouth-feel compared the SU-1. I would also like to point out that my SU-1 has been modified to accept and external power supply. I use mine with an Sounds Affairs Plixir Elite Balanced DC power supply.
Modified SU-1 pudding performs at a much higher level than stock pudding, so I can assure owners of stock SU-1 units, that the SU-6 performs at a much higher level. That leaves the comparison then between the modified SU-1 and stock SU-6. Price wise, the SU-6 commands only a small premium, after you take into account the cost of modifying the SU-1 backplate, and an aftermarket power supply.
The SU-6 offers a high level of information retrieval, with a silky and refined top-end and controlled bass with the right amount of tightness and bloom. Midrange is more laidback and richer compared to the SU-1, but is still detailed and textured. You do not get the feeling of information being smoothed over, but yet music is at all times very well behaved.
I would argue that the SU-1 is tonally more neutral, but without the refinement and fine resolving power of the SU-6. The SU-1 also comes across sounding as somewhat clinical and dry, especially through the SPDIF outputs. This required careful cable matching to balance out the tone. In this respect, the SU-6 is more cable agnostic. You are also able to tune the SU-6 through choice of power supply.
To be continued ...