Importance of clocking

@greg_f I remember that Weiss DACs had Firewire. I had Firewire HDs with my old Mac computer and used them with the newer generation with an adapter. Advantage of Firewire was that it had, being extension bus, sustained bandwidth. Peripheral buses like USB don’t have that running under protocol. This sustained bandwidth made it very popular in Audio/Video industry. The great feature of Firewire - Direct Memory Access (DMA) killed it. Once somebody made pocket Linux to run on the phone it made it dangerous. Hackers could connect it to portal in large company and bypass (or even obtain password).

You can try it. Other than that you have only choice of coax or Toslink. I use Toslink because of my DAC’s very strong jitter suppression to avoid electrical noise injection and possible ground loops. On the negative side Toslink drivers have slow edges making it noise susceptible (noise on the edge modifies threshold point affecting timing). Toslink works better when system is clean of electrical noise. Faster edges of coax are less sensitive to noise but create another problem - reflections from characteristic impedance boundary. You need to use impedance matched cables possibly 1.5m or 2m long (to make first reflection miss original edge) or very short cable, Rule of thumb is that transmission line effects (reflections) start when propagation time one way is longer than 1/8 of transition time. For typical 25ns transition 1/8 is about 3ns making it 0.6m cable (assuming 5ns/m). Since it includes all wiring inside on both ends I wouldn’t go further than a foot. The shorter the better. As for the conversion from USB - that might be good, especially if it contains electrical isolation.

@kijanki Thank you for the response. I enjoy reading your replies since you seem to understand electronics better than most on this site. Sometimes it is difficult to have a technical conversation with people who have little knowledge even about the basic concepts but they call themselves experts. I find audio a strange field... Your analysis on transmission line is spot on. For spdif I rather have proper 75 Ohms BNC terminated cable than with RCA plugs, I had an argument with somebody who was saying it is only audio, there is nothing high frequency so no need to worry about reflections, what he forgot is that reflections are caused by the rise/fall time of the edges and not the waveform frequency or data rate. Anyway, I diverted :)

Yes, yes, I much rather use Firewire than USB, in fact I still use a PC (with very little optimazation) with a PCIe Firewire card into the Weiss. But Firewire is getting old and new device of course don’t support it. I also use the Weiss AES i/f which is not too bad, almost as good as the Firewire. As I am interested in Qobuz, my next purchase is going to be a streamer, the way I see it is either fully optimize my server (both hardware and software), use the Firewire card and hopefully find some software that will support it, or buy a relatively decent streamer like Lumin/Innuos/Aurender and possibly a DDC as USB look like being the most common i/f these days. Unfortunately where I currently live there is no way to demo anything so I have to buy by what I read on forums and reviews... not the best way.

This thread has become a full time job, with terrible work life balance and benefits so I'm checking out after pretty much saying everything that I felt I needed to share. 

Best of luck and happy listening.

@greg_f   You can try USB to Firewire adaptor (or cable).  They are about $5 on Amazon - might work.

@greg_f   I forgot that it is specific Audio USB and Firewire.  AES seems to be the best choice.