Re: need help choosing between line level cables

"Eeyore" <rabbitsfriendsandrelations@[EMAIL PROTECTED]
> wrote in message 
news:4805053C.B87E5A5F@[EMAIL PROTECTED]
>
>
> Richard Crowley wrote:
>
>> "jakdedert"  wrote ...
>> > I dimly comprehend what he's talking about.  Since there is no actual
>> > earth ground at the unbalanced input--and no connection to the output
>> > equipment ground--the ground connection plus the signal hot would
seem 
>> > to
>> > form a differential input.  Possibly there is some issue with his/my
>> > logic, but it would seem to be feasible.
>>
>> In these days of home entertainment systems which include
>> video equipment, the chances of a completely ungrounded
>> system is also slim to none.  Whether video comes from a
>> cable system or from a DBS satellite dish/receiver, they are
>> very likely grounded, and a very common cause of ground-
>> caused problems, notoriously hum. RF transformers which
>> break this ground connection are becoming common in the
>> home-theatre industry.
>
> NONE of the home AV style equipment I have here has a mains earth, ALL
of 
> it has
> only 2 conductor mains leads.
>
> I'm talking about the CD player, DVD, cable TV tuner, VCR, Amplifier and

> tape
> deck. I dare say the screen of the incoming cable feed is grounded but 
> there's
> no way for it to make a loop.
>
> Graham
>

And there, I think, is the core of the issue. You are talking about 
equipment that floats free of earth, and you're using the whole equipment
as 
a differential input. However, as the balance to earth is very poor, the 
common-mode rejection will be very small. It may avoid earth-loops, but
will 
do little to avoid other forms of interference. It is also highly
dependant 
on there being no, or at best only one connection to earth anywhere in the

system. As soon as you have two, the potential for hum loops exists. Far 
better in my mind is to balance everything properly.

To paraphrase I think, John Linsley Hood, you can always cut down on
safety 
margins if you have complete control over cir***stances. In your case, 
anyone making an equipment change at some stage in the future could set up
a 
hum-loop.

S.

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