Re: need help choosing between line level cables

"Don Pearce" <nospam@[EMAIL PROTECTED]
> wrote in message 
news:4805a59f.541968312@[EMAIL PROTECTED]
> On Tue, 15 Apr 2008 13:41:20 +0100, "Serge Auckland"
> <sergeauckland@[EMAIL PROTECTED]
> wrote:
>
>>"Don Pearce" <nospam@[EMAIL PROTECTED]
> wrote in message
>>news:480497bb.538411812@[EMAIL PROTECTED]
>>> On Tue, 15 Apr 2008 07:52:51 -0400, "Arny Krueger" <arnyk@[EMAIL PROTECTED]
>
>>> wrote:
>>>
>>>>"Eeyore" <rabbitsfriendsandrelations@[EMAIL PROTECTED]
> wrote in
>>>>message news:4804960C.2046F6A0@[EMAIL PROTECTED]
>>>>
>>>>> Balanced wiring only gives you an advantage if the
>>>>> equipment is balanced. With clever wiring it's only
>>>>> actually necessary for either the 'sending' or
>>>>> 'receiving' equipment to have a balanced input or ouput
>>>>> but you need to know what you're doing in this case.
>>>>
>>>>I know the strong advantage that balanced inputs give, but what 
>>>>advantage
>>>>do
>>>>you get from an electronically-balanced output driving an unbalanced
>>>>input?
>>>>
>>>
>>> Provided you have an appropriate balun, like a transformer at the
>>> input, you get all of the advantages.
>>>
>>> d
>>>
>>> -- 
>>>
>>> d
>>
>>Yes but then you're driving a balanced input aren't you ;-)  If you have

>>an
>>electronically balanced output (hence usually but not always referred to
>>ground) driving an unbalanced input, I can't see what real benefit you 
>>will
>>get however clever you are with wiring. What you use a balanced system
for
>>is to get rid of common-mode noise, usually in the form of hum, but also
>>higher frequencies. Unbalancing at the receiving end will remove the
>>common-mode rejection.
>>
> You are right of course. Maplin have stereo audio transformers that
> work very transparently for isolation at under £10 apiece.
>
> http://www.maplin.co.uk/Search.aspx?criteria=vw43w&source=15&SD=Y
>
>
>>If I were doing what the OP is doing, I would wire my house with CAT5/6
>>cable which is really cheap these days, then use equipment with balanced
>>I/O.  As already mentioned, CAT5/6 can carry 4 balanced audio signals,
so
>>you either get 2 stereos or a send and return stereo pair in each cable.
>>Crosstalk isn't an issue with balanced operation. If suitable balanced
>>equipment isn't available, then there are some alternatives.
Transformers
>>are definitely one, and they have the advantage of fully-floating 
>>operation
>>and galvanic insulation. However, good transformers are expensive, 
>>although
>>it's not necessary these days to have transformers which will drive 600 
>>ohm
>>lines, 10k-10k transformers are somewhat cheaper. Other alternatives are

>>to
>>get some pro units like the Henry Matchbox which lists at $225 for a
>>bi-directional interface, therefore equivalent to 4 transformers.  I
would
>>guess that the street price for the Matchbox is under $200 and as these
>>things don't wear out, it may be possible to buy these on EBay for half 
>>that
>>price.
>>
>>Whatever way you do it, I would not even think about using unbalanced 
>>wiring
>>however well screened, as once incor****ated in the house, it can't be
>>changed.
>
> CAT5 is possibly the way to go. Are you sure about the crosstalk
> though? With digital signals it is only necessary to get better than
> about 10dB of isolation. I would want better than 90dB for audio,
> particularly if carrying unrelated signals.
>
>
> -- 
>
> d


I haven't measured the crosstalk using CAT5 cable myself, but I know of 
several radio stations that use unscreened multi-twisted-pair bundles for 
line-level analogue audio and have no crosstalk issues(The multi-pair
cables 
have one overall screen, but the individual pairs are unscreened.)  The 
twisted pairs in CAT5 cable are pretty tightly twisted, and using today's 
low output impedance sending, (typically less than 100 ohms) I would not 
expect cross talk with line-level signals to be a problem. Clearly, I 
wouldn't use CAT5 cable for microphone feeds, but for line-level I would 
expect it to be fine.

S.
-- 
http://audiopages.googlepages.com