konut wrote: > The prevailing wisdom asserts that no RCA termination will give a true > 75 ohm result. Then again if the source and DAC were designed to be > impedance optimized with the RCA jacks then this wouldn't really matter.
Unfortunately impedance was not a design characteristic of the RCA plug, in actuality they vary all over the place, from something like 25 to 45 ohms or so. They were designed as cheap audio plugs with no thought that they needed tight impedance characteristics for RF frequencies. BNCs OTOH WERE designed as RF connectors so do include impedance as a design spec. Speaking of impedance and BNCs, they come in two flavors, 50 ohm and 75 ohm. They are interchangable from a mechanical perspective. The 50 was the original version and existed for a long time in the marketplace. Then someone realized that you could take off some of the solid insullation and make it air insullated and presto, its 75 ohms, perfect for 75 ohm systems such as S/PDIF. Unfortunately MANY companies that sell 75 ohm cables with BNC connectors use 75 ohm cable but use 50 ohm connectors! I did a very unscientific sampling of cables available on the internet and found that only 30% used real 75 ohm connectors. So even if you get equipment with BNCs make SURE it uses a 75 ohm jack and that you get cables with 75 ohm plugs. And it's not just "audiofile" companies that get this wrong, I bought some cables from several cable places that specialize in selling cables to pro broadcast customers and their 75 ohm cables had 50 ohm connectors on them! I'm completely at a loss to understand how this happens, that a cable company doesn't know the difference and the "professional" customers don't either. It's interesting that Blue Jeans gets it right, they are inexpensive yet extremely high quality cables done right. John S. ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=95614 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
