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S/PDIF-how different than an IC?

I posted this on "Cables" too. One has a 75 Ohm spec and one does not. One comes in pairs and one comes as a single. Both typically have RCA's though some have BNC's. How does a cable producer change the spec on what outwardly appears to be an identical cable? If you specify from a cable producer that you want an S/PDIF how do you know they are not simply selling you one half of a pair of off-the-shelf IC's? And last but not least, how does 75 Ohm change the sound one would hear from a normal IC (when carrying digital signal rather than analogue of course)?
I know this much; a very well-respected engineer with a Ph.D. in EE who designs and produces DAC's of his own says that you are free to experiment with using a normal IC with his DAC's rather than a dedicated S/PDIF.
128x128fsonicsmith

Showing 4 responses by auxinput

auxinput
2,920 posts
 
Tell me, what "special" RCA exists for an SPDIF cable? 
auxinput
2,920 posts
 
Like others have said, you can technically use a standard IC for a digital S/PDIF connection.  It will work because they are both just a wire that is connected using RCA plugs.  However, the IC is likely not going to perform as well because of the shielding and impedance requirements of the S/PDIF specification. 

The specificaion states a recommended use of BNC connector due to the 75 ohm design.  Most manufacturers just use RCA because this was a trend started a long time ago.  The problem is that RCA has an actual impedance of about 30-35 ohms.  This means it is more likely to have signal reflection problems.  This occurs when the digital pulse hits the receiver on the DAC side and actually produces a pulse reflection (like a sound wave reflected off a wall).  That reflection travels back down the cable to the source and causes distortion and inaccuracies on additional transmitted pulses.  The audible result is loss of high frequency resolution or other audio inaccuracies. 

Also, I always recommend 2 meter cable minimum to reduce reflections, even on BNC cables.
auxinput
2,920 posts
 
Now I have ordered a custom made 1.5M S/PDIF using the Silver Apex conductor and construction from Analysis Plus.

I have found that BNC cables with a BNC-to-RCA adapter actually perform better than a cable with only an RCA connector on the end.
auxinput
2,920 posts
 
Pasternack makes an RCA connector that is very similar to the Canare.  It has the internal brass pin that is inserted into the RCA connector itself.  This is the same idea of a BNC-to-RCA adapter.  I don't know about the Canare, but the Pasternack was really crappy.  It presented a harsh/bright sound.

The best BNC-to-RCA adapter I have tested is the Black Cat BNC-to-RCA adapter.  It has the best and most transparent resolution.  The Black Cat doesn't have super grip on the plug, but it sounds better than other adapters.  The Canare adapters are soft and distorted.  Probably the next best adapters are the gold-plated cheap Monoprice type adapters.  These are the exact same adapters that Nordost includes on their cables.  The gold-plated design presents a slightly warmer sound with slightly more rolled-off highs.
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