Hi,
On Saturday 15 August 2009 21:04:22 Brent Busby wrote:
Is it wrong to use a regular cable (no transformer) to
connect the XLR
main and submix group outputs of a console to the TRS (balanced) inputs
of an audio card, or should impedance matching be done in that case?
It is quite common in music stores these days to find cables that are
XLR male on one end and TRS male on the other. (I'm currently using
those on my mixer outputs.) The cables *are* balanced, but they do not
contain a transformer at all.
The impedance of my console's main/submix outputs is rated as less than
75 ohms, but the input impedance of my audio card is 10k ohm. This
would seem to almost answer the question by itself, it weren't for the
near impossibility of actually finding a matching transformer that's TRS
and not TS on its 1/4" end. I looked at a lot of them. They're all
made for hooking up guitars, amps, and mics, and they all seem to have
an unbalanced plug opposite from the XLR end.
There is absolutely no need to do any transformation in that chain. Balanced
to balanced is pretty good.
Afaik impedance-matching doesn't necessarily mean that all impedances have to
be the same, they have to match. So if the output of the mixer has <75Ohm
compared to the input impedance of the soundcard of 10kOhm, it means that
almost no energy is lost at the output and all is "lost" at the input. And you
want the energy of the signal to be lost at the input so you can use it. This
is when you need the signal, not the power. For speakers (and for solar-
modules) you want the impedances to be about the same so the efficiency is high.
For more I have to get out my "physics for engineers"-book...
Have fun,
Arnold