How much degradation because of RCA-->BNC adapter

There wont be a difference.

Really? I've heard the plugs are important for the sound quality in interconnects..hmmm...

Good luck hearing a difference.  Hint: you won't

It will really depend on the type of power cord you are using. I am recommending that one:

http://eandt.theiet.org/news/2011/nov/power-cable.cfm

There are two types of cables and plugs that use BNC connectors: 50 Ohm and 75 Ohm. The latter is used for S/PDIF digital. If everything in between the devices doesn't have a 75 Ohm characteristic impedance then you get signal reflections, which is not a very good thing. RCA plugs aren't 75 Ohm. How much does it matter? That's not an easy thing to answer. Not really that much for most people. If you've spent a huge amount of money on digital gear, then maybe it does. My experience says it depends on the DAC.

Anyway, for fun, here is a crappy measurement attempt on the digital output of my USB converter. Note that the cable used in the green graph had RCA plugs on the end, which aren't 75 Ohm spec. Also, it wasn't an S/PDIF signal being sent out, so the differences may be more or less significant than what is shown when an actual S/PDIF signal is sent.

Quote:

Originally Posted by Currawong 

Some months ago, I bought an Oscium iMSO-104 which attaches to an iPhone or iPad to turn it into an oscilloscope of sorts. My thought was that I could get some vague idea of what was going on with some of my equipment by measuring things. Vague indeed it has been as the main analogue probe is 50 Ohms, making it less than ideal for measuring anything digital and it picks up interference easily, resulting in less than a perfect picture. Here are some measurements I took on a whim of various things. Don't read too much into these graphs as the last time I used an oscilloscope was in elementary (primary) school!

 

Test wave from an Audiophilleo 1 directly from the socket (white) and with a Canare RCA 75 Ohm cable + adaptor (green). The spurious bumps are from interference and should be ignored. The only thing I think is of note is the slightly rounded shoulder of the square wave after adding the cable.

 

Quote:

Originally Posted by korzena 

Dont interconnects and plugs matter at all?

See the sound science forum. :)

Some people on some systems hear differences some of the time. What kind of differences seems to be inconsistent and prone to vanishing when objective measurements are made. Caveat emptor. 

I buy decent cables because I feel better about the build quality and I like assurance of solid connections. Beyond that, I don't worry about it. Thus far cables have not been shown to have any audible impact, provided that they are solidly connected and can carry enough signal/current for their use.

BNC adapters are not good so I would avoid using them. The cable you are using is really a coax cable but uses RCA connectors. Coax cables have RF shields, a braided wire or an aluminum foil, in some cases both for better RF protection. Like Currawong explained, there are two standard BNC connectors, 50ohms and 75ohms. If you use the wrong one, there will be a drop in signal strength, I can't recall how much due to impedance mismatch.

Also the 75ohm and 50ohm BNC connectors' center pin diameters are not the same, one is slightly larger than the other. If they don't match, you can break the female connector in your DAC and transport or the connection will be loose. The BNC cable also has RF shielding.