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Another s/pdif digital cable thread

When I set up my system and cabling some years back I was blissfully unaware of difference between 75 ohm and 50 ohm BNC connectors.  I just thought BNC was BNC.  Most of my digital gear already has 75 ohm BNC female connectors for s/pdif inputs & outputs.  Some, however, has RCA sockets.  On close inspection I recently discovered that the cables all have 50 ohm RF connectors.  And a couple are 50 ohm BNC at one end and RCA at the other. 

IOW, it's a connector and impedance mashup salad and I want to sort it out right.  First, the 50 ohm connectors will get scrapped and replaced by proper 75 ohm connectors.  Then I'll use 75 ohm BNC => RCS adapters instead of the BNC/RCA frankencables.
So here's the question:  how much degradation do all these mismatches create?  Seems like there should be a ranking of these scenarios.1. Proper 75 ohm BNC + 75 ohm coax everywhere.  The right way, next step.
2. [50 ohm BNC connectors + 75 ohm cable] to [75 ohm equipment connectors].  What I got now.
3. [75 ohm BNC + 75 ohm cable + RCA] to connect "mixed" equipmen.  Also what I got now.
4. [75 ohm BNC connectors + 75 ohm cable] + BNC/RCA adapter to [mixed equipment connectors] .  Next step.

Any comments or suggestions would be great.  I'm hoping for a big improvement - but time will tell.  Thanks,
raueda1
5 responses Add your response
raueda1 OP
20 posts
 
And a further question arose.....
2 units have RCA s/pdif connectors.  From what I've read - I think - it's better to connect them with a proper 75 ohm BNC cable and BNC/RCA adapters at each end rather than just a "digital" RCA cable?
FWIW, part my the problem is having 3 s/pdif sources and a DAC setup with just 1 s/pdif input so there's some signal selection stuff inserted into all this.  TosLink would solve much of it but I want to avoid that.  Why do they still even use it anyway?
teo_audio
2,197 posts
 
The adapters cause jitter/reflection/mismatch/non-uniformity problems. 

Likely they cause more problems than just RCA to RCA on both ends. So, no BNC connected cable, with adapters, just go pure RCA.

For RCA, goe RCA to RCA.
For BNC, go BNC to BNC.

Adapters might make it all work, but they cause slight jitter issues all on their own, is the thing.
raueda1 OP
20 posts
 
Thanks, not surprising. I’ll scrap the adapter idea. But problems arise. Some (more like many, I guess) say a true 75 ohm RCA plug is an impossibility. Nevertheless, there are manufacturers selling plugs claiming to be 75 ohms and RG-59 cables with RCA terminations. Maybe these really aren’t 75 ohms but somehow close enough? Or they assume that nobody could tell the difference anyway?

Regardless, I have a choice to make. I’ve got a Node 2i streamer with RCA digital output. That connects to a digital input selector with an RCA input (among others). I don’t want to mess with the Node 2i but I’m happy to mess with the switch. So I’ve got 2 choices:1. 75 ohm cable with "75 ohm" RCA terminations, or,2. Replace RCA socket on the switch with female BNC. Then use 75 ohm cable with BNC on one end and "75 ohm" RCA on the other.
First world problems, to be sure. Suggestions on which? Thanks,
auxinput
2,920 posts
 
Huh, I had the complete opposite result when using BNC-to-RCA adapters.  On the exact same cable, I had much better high frequency resolution and results with using BNC connectors on the end of the cable and them BNC-to-RCA adapters.  When using the same exact cable with only RCA plugs, I lost high frequency resolution and air in the sound.  I used the best RCA plugs as well.
jtcf's avatar
jtcf
1,620 posts
 
No cable or connector is going to pass the signal perfectly.Get some adapters and see what sounds best to you.I've actually had very good sound using an XLR cable with adapters before,which seems ridiculous.It hurts nothing to try :-)
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