[Occam]

Dave,

It doesn't matter what impedance a RCA plug has. What matters is what impedance the combined RCA plug and RCA socket has. Plug in those nominally 75 Ohm plugs into a 'normal' RCA socket and you've got a 30-50 Ohm impedance. To my knowledge (not verified by personal use or measurement) the only RCA plug/socket pairing that presents a complete 75 Ohm impedance is the WBT Nextgen RCA plug and socket.  FWIW

-Paul

[DaveC113]

Dave,

It doesn't matter what impedance a RCA plug has. What matters is what impedance the combined RCA plug and RCA socket has. Plug in those nominally 75 Ohm plugs into a 'normal' RCA socket and you've got a 30-50 Ohm impedance. To my knowledge (not verified by personal use or measurement) the only RCA plug/socket pairing that presents a complete 75 Ohm impedance is the WBT Nextgen RCA plug and socket.  FWIW

-Paul

Yes, that is a good point!

Canare offers a 75 ohm female connector as well...

http://www.canare.com/ProductItemDisplay.aspx?productItemID=101

[Occam]

...
Canare offers a 75 ohm female connector as well...

Good to know. Thanks. - Paul

[srb]

It's interesting that using a 75 ohm cable with mismatched non-coaxially terminated RCA plugs (WBT 0144) that should likely result in unwanted signal reflections and square wave corruption, I still believe I hear a more solid and focused sound than with the Toslink optical connection that has no inherent mismatch.

Most of the articles and test reports I have read where they had the proper test equipment usually measured significantly higher jitter with the optical connection than with the coaxial.  I guess this is to be expected when inserting another conversion layer in the signal path to convert electrical S/PDIF to optical and back again as well as the possible suspect quality of many inexpensive Toslink transceiver chipsets.

I'm not sure how much the impedance mismatch of RCA connectors affects the sound, but those who have sources and DACs with BNC, XLR and RCA connectors at least have the ability to do a rapid input switching A/B comparison to get some idea of real-world sound differences between BNC, XLR, regular RCA and "true" 75 ohm RCA, beyond electrical theory alone.

Steve

[jcotner]

I use a scope to check every digital path I wire.
There is no substitute for checking signal integrity
at the receiver point.
One  thing you guys don't really mention is the
affect on clock recovery as the edges degrade.
I'm not sure about the common DAC chips, but
most of the digital circuits I've worked on do
some sort of clock recovery from the incoming
signal (unless a separate clock is provided on
another pair) in order to correctly sample
incoming data edges into some sort of input flip-flop
for the rest of the chip.
AES is also differential and most  modern
differential transmitters can drive a very wide
range of cable and connector conditions with
little impact to signal quality.
BNC started life as an RF connector and it's
used quite extensively in the test equipment
world where low noise is expected from DC
well into the 200MHz range. That makes it
a natural for digital signals but I don't think
it offers superior performance to an XLR
cable in the differential world.
My two cents.

[Napalm]

A terminator is one thing and a connector is another!  Get out your Ohm-meter and measure the terminator, it will read it's listed value.  Measure a connector and it will read near infinity.  For a rather low frequency circuit like S/PDIF the connector is not a factor.  For short interconnects like 1 or 2 meters the co-ax is not a factor either.

I suggest you measure both the connector and terminator at something like 10-100Mhz and post the results here.

S/PDIF was designed to use rectangular ("digital") signals.  By any means they are not "low frequency". An ideal rectangular signal has an infinite spectrum.

[livengood1]

I use a scope to check every digital path I wire.
There is no substitute for checking signal integrity
at the receiver point.
One  thing you guys don't really mention is the
affect on clock recovery as the edges degrade.
I'm not sure about the common DAC chips, but
most of the digital circuits I've worked on do
some sort of clock recovery from the incoming
signal (unless a separate clock is provided on
another pair) in order to correctly sample
incoming data edges into some sort of input flip-flop
for the rest of the chip.
AES is also differential and most  modern
differential transmitters can drive a very wide
range of cable and connector conditions with
little impact to signal quality.
BNC started life as an RF connector and it's
used quite extensively in the test equipment
world where low noise is expected from DC
well into the 200MHz range. That makes it
a natural for digital signals but I don't think
it offers superior performance to an XLR
cable in the differential world.
My two cents.

I have tried many coax cables over the years, most recently the Lessloss coax for the past few years. After reading about potential problems caused by reflections, impedance matching, etc., I tried several cables of different lengths to see what difference (if any) would become manifest, and an inexpensive 10-foot Canare cable outperformed my expensive Lessloss cable, as well as the same cable in different lengths. I then decided to try Toslink and was amazed that it was the best yet. I can do instant switching comparisons and there is no doubt in my mind that the Toslink is much better. I now have a Wireworld Supernova glass cable that sounds better than any cable I have yet tried. I don't have the answer, but it just sounds better. I suppose it is useful sometimes to question the "known facts" that we have been fed.