"Arfa Daily" wrote in message
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"Andy" wrote in message
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On 25 Apr 2006, Dave Plowman wrote:

600- 600 ohm transformers are used on balanced pro equipment. Or
more likely once were in valve days. Most balanced audio these days
is low impedance out high in - same as domestic.

Ground isolating transformers these days will be usually 10k in and
out.


Wow, now that's got me confused!

I am not using old tube equipment and I'm not using pro stuff either.
Instead of 600-600 ohm, you seem to be saying that I need 10K-10K ohm.

Can you or someone else explain this a little please.

10K-10K seems very different from the 600-600 which I was about to get!



It's all starting to get a bit confused now, isn't it ? 600 ohms is the '
pro ' standard for audio transmission lines, and is usually, although not
always, a balanced line system. Mics with XLR connection systems are often
600 ohm matched, and balanced, although may be 10k if they don't contain a
600 ohm line matching transformer.

You don't say exactly what pieces of kit you are trying to isolate from
one another, but assuming it's a couple of items operating at ' standard '
line levels - such as a CD player, or tuner, or cassette deck, feeding
into the corresponding input of an amplifier, or the aux in, then the
likely impedance both ends will be around 47k. Obviously, 600 ohms is not
a terribly good match to 47k, but it's probably about the best that you're
going to do with readily available
1 : 1 line matching transformers. I would suggest that you just give it a
try. There will almost certainly be some effect on the overall frequency
response of the system, but depending on what you listen to, or how
critical your ear is, this may not be an issue, and might possibly be
largely overcome-able by judicious use of the system tone and equalizer
controls.

I have used 600 ohm 1 : 1 line matching transformers on several occasions,
to do what you are trying to accomplish, and have never had any real
problems with the finished audio.

Arfa

Actually, thinking about it, 22k is probably a more realistic figure for
line level inputs, as opposed to 47k for a phono input, but everything else
said, still applies.

Arfa