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Impedance question

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Posted on October 29, 2015 at 10:12:15
thom70
Audiophile

Posts: 81
Location: RM
Joined: June 26, 2007
 To have a real 75 ohm impedance on the digital cable is better to have a digital cable having both sides rca connectors (altough not 75 ohm) or cable having one side rca and the other bnc?
I remember I read somewhere that it's important have the same impedance (altough not 75 ohm)both sides of the cable, so I guess we should avoid rca/bnc cables and use only rca/rca or bnc/bnc cable?
Thom

 

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RE: Impedance question, posted on October 29, 2015 at 16:37:24
PingPing
Audiophile

Posts: 196
Joined: May 22, 2014
 is this cable used as a Digital (SPDIF) cable?

 

RE: Impedance question, posted on October 30, 2015 at 05:32:23
thom70
Audiophile

Posts: 81
Location: RM
Joined: June 26, 2007
 Yes.
Thom

 

RE: Impedance question, posted on October 30, 2015 at 05:52:02
PingPing
Audiophile

Posts: 196
Joined: May 22, 2014
 rca connectors at both ends is fine :)

 

RE: Impedance question, posted on October 30, 2015 at 14:32:43
PingPing
Audiophile

Posts: 196
Joined: May 22, 2014
 also rca's are the most convenient and have been widely used :)

 

75 ohm characteristic impedance, posted on October 30, 2015 at 16:05:12
Duster
Manufacturer

Posts: 17117
Location: Pacific Northwest
Joined: August 25, 2002
 The 75 ohm characteristic impedance of a coaxial cable should be maintained (not poorly affected) by the cable termination method.

The most important factor is to terminate a digital cable with a connector and termination method that maintains the 75 ohm characteristic impedance of the dielectric topology at both ends of an S/PDIF digital cable, regardless of BNC vs. RCA. While BNC connectors tend to be better optimized by design for 75 ohm applications, an rca connector can provide audiophile quality performance without concern. The 75 ohm friendly rule is to not deform (such a crush or pinch) the ends of the cable when terminating it with a connector.

This means don't use connectors that rely on rough crimping or invasive set-screws that impinge on the should-be pristine-cut ends of the cable. The reason for such a fuss is to avoid cable reflections due to deforming the 75 ohm characteristic impedance of the dielectric (the insulation between the center conductor and the shield). Again, the fundamental issue is the 75 ohm characteristic impedance of the coaxial cable should be maintained by the connector and termination method. That said, you can terminate a digital cable with a BNC connector at one end, and an rca connector at the other end (if it's done right).

 

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