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Diy digital Coax cable

glenn jarrett

glenn jarrett

pfm Member
Hi
just wondering if this cable would be any good for a digital coax cable from my digi hat to DAC would only need to be 0.6m
The cable was out of a Qed scart lead quite expensive at the time and looks like solid silver or silver plated
will also make a pair for my turntable 20200512_122635 by glenn jarrett, on Flickr
 
If it was a decent SCART lead it would be 75 ohm coax so perfectly suitable for a short digital coax interconnect - at the low audio data rate and short distance it`s not a critical application, unless you have RFI / earthloop problems in your system.
 
glenn jarrett said:
just wondering if this cable would be any good for a digital coax cable from my digi hat to DAC would only need to be 0.6m
The cable was out of a Qed scart lead quite expensive at the time and looks like solid silver or silver plated
Click to expand...
Since you already have the cable, it can't hurt to try and see. As already suggested, coax from a SCART lead should be fine.
 
That coax looks reasonable.
Many video cables have no shield at all, just a drain wire, so not actually coax
 
Yomanze said:
With RCAs, it's not possible to maintain that impedance, so does it really matter if it's 75R or 50R...? This is why I use 75R BNC.
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The S/PDIF bandwidth is low enough that the impedance isn't very critical. If it was a problem, they wouldn't have used RCA connectors in the first place.
 
Yomanze said:
With RCAs, it's not possible to maintain that impedance, so does it really matter if it's 75R or 50R...? This is why I use 75R BNC.
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Oh yes it is! As mansr says it's not that critical anyway but RCA phono plugs, although not designed for RF, happen to be in the region of 75R and make decent RF connectors up to 100MHz plus.
 
Arkless Electronics said:
Oh yes it is! As mansr says it's not that critical anyway but RCA phono plugs, although not designed for RF, happen to be in the region of 75R and make decent RF connectors up to 100MHz plus.
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I do think there are benefits with properly terminated cables (BNC) and also ensuring that the output / input stages maintain this 75R impedance.

RCAs are more like 20 to 30 Ohms...
 
Arkless Electronics said:
You are wrong then.
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I don't think so...

"The old-style RCA (phono) type solder plugs have an impedance characteristic of approximately 25 ohms, and exhibit extremely poor Return Loss performance when mated with professional 75 ohm coaxial video cable. "

https://www.canford.co.uk/CANARE-RCA-PHONO-CONNECTORS-Male-cable-types-Crimp

Yes, Canare claim to have special RCAs that are "true 75R", but this is not just possible with the dimensions of the plug / socket interface.
 
Yomanze said:
I don't think so...

"The old-style RCA (phono) type solder plugs have an impedance characteristic of approximately 25 ohms, and exhibit extremely poor Return Loss performance when mated with professional 75 ohm coaxial video cable. "

https://www.canford.co.uk/CANARE-RCA-PHONO-CONNECTORS-Male-cable-types-Crimp

Yes, Canare claim to have special RCAs that are "true 75R", but this is not just possible with the dimensions of the plug / socket interface.
Click to expand...

That is wrong. They are close enough to 75R. Phono's were used until recently for RF between internal screened boxes in VCR's and TV's. End of conversation.
 
Yomanze said:
I don’t think these use bi-phase mark encoding like SPDIF. You don’t need to worry about recovering a clock...
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The bandwidth requirements are similar for S/PDIF and standard-definition composite video.

With analogue video, poor connections often result in visible ghosting. The fact that a clean image can be obtained is proof that the connector is adequate.
 
mansr said:
The bandwidth requirements are similar for S/PDIF and standard-definition composite video.

With analogue video, poor connections often result in visible ghosting. The fact that a clean image can be obtained is proof that the connector is adequate.
Click to expand...

Now we are getting somewhere. With digital audio, impedance mismatches cause something akin to this “ghosting” effect you refer to, which doesn’t affect to the data side, but to the clock signal.

How well the SPDIF receiver de-jitters this otherwise perfect data is a different matter
 
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