<> wrote:
> I think you are being over cautious/through, I don't have figures
to hand
> but recall when I tested a 100m (330ft) reel of starquad used as
stereo the
> Xtalk was in the -100dB region across the 20-20kHz range.
That's good. Do you recall if you were using line or mic level
signals?
JL} Both, including elevating the interfering re the interfered with chan.=
Mostly this was to overcome the noise of my measuring meter.
This is pretty interesting re using Cat 5/6 cables
http://www.belden.com/pdfs/Techpprs/Cat5AV.pdf
Go to page 6 for use / performance with balenced audio.
> ** The perfomance will of course depend on the common mode
abilities of the
> gear & a low source impedance helps a lot too.
Most electronic audio gear performs reasonably well in those areas
these days, although some microphone have a higher output Z than
desired. The Royer SF12 stereo ribbon mic, for example, has/had an
output impedance of 300 ohms. Okay for short cable runs, but not long
ones.
JL} See table 5 on Page 5 in the Belden doc for info re this. It seems to
suggest a typical starquad cable & 300 Ohms will give a 1dB drop at 20kHz
with about 130metres of cable. The 300 Ohm is at 1kHz I ussume and may well=
vary quite a bit at other frequencies.
The following is a moot point based on your measurements above, but,
from a theoretical point of view, I wonder what the nature of any
induced signal would be, from one channel to the other, when using
star quad? Would it be predominantly common mode, or differential?
JL} I have faith in the cable manufactorer's ability to match each pair to=
each other to a hi standard. And the Xtalk IMO will be mostly down to
impedance matching of the mic amp differential input (BTW with good mic amp=
s
such as the Alice Matchamp's I was using I did the measurements without
phantom power on & also with the two 6k8 phantom resistors out of circuit -=
I have found the matching of the 6k8's needs to be within .1% to not mess u=
p
the CMMR)
John L
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