SMSL SU-8 acting weird with digital coax input
Jun 17, 2019 at 12:20 AM Thread Starter Post #1 of 4

Allegro maestoso

100+ Head-Fier
Apr 25, 2019
Utah, USA
Hey all,

My SU-8 sounds lovely - I've had it for a couple of weeks - but today presented a connectivity hurdle. I wanted to output my FiiO's digital coax signal to my Mimby and my SU-8 simultaneously, so I bought a coax splitter from Radio Shack:


and some coax cables and F-connecter to RCA adapters from Amazon:


I already had a FiiO TRRS to digital coax cable:


So I connected the FiiO to the Input side of the splitter, the Mimby to one of the outputs, and the SU-8 to the other. Then things got weird. The Mimby acted all cool and was like, "Yep, that's a digital signal. I know exactly what to do with that - I'll turn it into something analog and output it to your amp. No big whoop." But the SU-8 was all like, "no sig". So I switched the output cables on the splitter, thinking cable or adapter or splitter problem. Same result: sound from the Mimby, "no sig, you dumb idiot" from the SU-8. Okay. So I disconnected the Mimby, continuing to run the FiiO through the splitter and out one side to the SU-8. Still "no sig". Connecting the FiiO directly to the SU-8 instantly changed the SU-8's display to "44.1 kHz" and it output sound like it always has with the FiiO directly connected.

Does anyone have any any idea why the SU-8 would reject a split coax signal while my Mimby is perfectly happy with it? There are diode symbols on the splitter, which suggests that it is one direction only. Could this have anything to do with it? Would it have been simpler and more effective to use something like this instead of a splitter (now that the thought finally occurs to me)?


Thanks for your thoughts.
Jun 18, 2019 at 11:42 AM Post #3 of 4
Modi MB and SU8 likely seems to have different threshold voltage levels to distinguish "0" and "1". And for some reason, after the splitter digital signal might be weaker than what SU-8 identify as "valid". If you really need such configuration (two dacs simultaneously), maybe active splitter (or digital-digital converter) helps.
Jun 29, 2019 at 8:57 PM Post #4 of 4
I finally got this to work, connecting the equipment as follows: FiiO X3ii -> FiiO brand 3.5 mm to RCA digital coax cable -> RCA Y-splitter -> RCA coupler -> two digital coax cables -> Schiit Modi Multibit and SMSL SU-8 DACs. Either of my sources can now feed either of my DACs, each of which can in turn feed any of my three amps, with no need to plug and unplug things. I wanted this configuration because some of my headphones sound better with a multibit DAC, and some sound better on a balanced rig. If I want to change headphones in the middle of a playlist, album, or song, it's as easy as flipping a switch and/or pushing a button.

Y splitter.jpg

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