BNC>BNC/Coax Adapter, BNC>Coax or Coax/BNC Adapter>Coax?

Audio Gear Everything else
#1

Hi there

New to the world of Volumio via RPI + Allo DigiOne ‘streamer’, and given that the amp that I am connecting my ‘streamer’ to only has coax digital inputs, I am connecting the ‘streamer’ via its coax, rather than BNC output.

But then reading a bit around the subject I find that BNC impedance is 75 Ohms whilst coax is 50 Ohms, so basically (as I understand it) the BNC connection is better in terms of jitter minimisation.

Then checking my amplifier I find that the coax inputs are rated at 75 Ohms, which suggests to me that I should use the BNC output from the ‘streamer’.

But that means that I have 3 choices for cabling up, i.e., a suitable quality digital cable, terminated:

  1. BNC to Coax
  2. BNC to BNC with Coax Adapter
  3. Coax with BNC Adapter to Coax

So my question is which of the above, assuming that digital cable is digital cable (good quality of course), which termination combo would be best from a sonic perspective, i.e., minimised impact on signal quality, etc.

From my readings I can find nothing definitive but though that perhaps the knowledgable folks in this Community might have advice to offer.

Many thanks in anticipation.

The Charbits

#2

Without becoming to technical, the impedance should match, to avoid reflection. COAX is a cable with specific characteristic, to minimize signal lost. (RCL network). If the output is 75Ω, you should use a cable of 75Ω and terminate it with 75Ω.
So in your case use a 75Ω cable with BNC on one side and COAX (RCA) on the other end., or and RCA COAX cable RG59, with an BNC 2 RCA adapter, like:

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#3

Thanks, Wheaten, much obliged.

What I now need to do is find out whether the cable I am using is specified as 50 or 75 Ohms…it is a coax cable I had from previous use and I assumed that it would be OK. Finger crossed it is but if not then I shall have to raid the piggy bank and treat myself to something more suitable. :grin:

Regards, The Charbits

#4

BNC connectors are available in either 50 or 75 ohms.
RF type coaxial cable is also available in either 50 or 75 ohms.

50 ohm has a larger centre conductor relative to the cable diameter.
If you put a 50 and 75 ohm BNC male plug side by side you can easily see the 75 ohms has a thinner centre pin (and the hole for inserting the centre conductor inside the connector will be too small to accept the 50 ohm cable’'s centre conductor.

75 ohm coax is usually associated with TV antenna systems and cable TV, RG59, RG6, etc.
50 ohm coax is usually associated with commercial and amateur radio systems, RG58, RG8, etc.

Audio coaxial cables like those used on RCA connectors and microphones don’t have the “characteristic impedance” noted as it is not carrying RF.

#5

Thanks pwstereo, for further clarifying. I have checked the cable out and it is a 75 Ohms one so as the output to it is 75 Ohms and the input from it is also 75 Ohms I think that I am set…no need to mess about with BNC to Coax adapters…unless someone can advise as to a reson to do so.

Regards, The Charbits