I am in the UK.
I would like to take a stereo signal from the line-out of my stereo
(or TV) to the line-in of my PC.
The equipment is in different rooms and the audio cable would be 10
metres. It will be this type:
formatting link
I don't understand the technical side but is 10 metres so long that
it might cause audio problems with things like frequency response or
voltage/current levels and so on?
Will I need to get some higher specification audio cable to cover
that distance? I want to keep cost down.
I have used similar cable for a similar purpose over longer distances
with no problems, for general purpose "listening" quality. Buying a
higher spec cable is only going to give a very marginal improvement - if
you really are interested in quality, you would link digital ports using
an optical cable and not use analogue, anyway.
You might get unacceptable noise pickup, you might not. Try. You
might also get hum. Sometimes it responds to simply lifting the
screen connection at one end, sometimes you need an isolating
transformer. Or rather a pair of them.
What's the link for?
The cable is most likely just fine. However beware of
ground loops and other hazards of running audio over
long distances. These have little to do with the cable.
Expanding on that a little:
My "trans-workshop cable" is about 8 metres long and works perfectly. It's
cheap audio cable (shielded of course).
The equipment on both ends is powered from the same electrical circuit and I
don't have ground loop problems. You would have ground loop problems if the
equipment were powered from different circuits. I gather that you are in
the UK (hence "ring" wiring structure, which I like, instead of the American
daisychain) and that everything is in the same room. It should work fine.
mc spake thus:
So how does house wiring work in the UK? Is there more than one
grounding ("earthing") point? And how is this better?
(Here, the Merkin practice is to ground the "service panel"--the box
where the big wires come into the house--to a single ground rod, with
everything running downstream from that.)
By the way, this brings up a strange experience I had recently doing
some wiring. I was working for a guy who owns two houses right next to
each other, and he wanted to run a cable TV connection from one house to
the other. I was about to connect the cable in the attic of the house
that was the source of the signal when I got a little tingle. After
grabbing a VOM, it turned out that there was about a 20 volt difference
between the two cable grounds.
Was this due to power line potential differences, or to cable signal
potential differences, or something else? The cable guys do their own
grounding outside, and I don't think they put in any bonds to the
electric service ground. In any case, the whole project was abandoned
then and there as a bad idea. (It occurred to me that a cable
transformer could have solved the problem, but then so could doing the
thing the right way: just getting both houses wired for cable.)
Mc doesn't understand ground loops. You can get them between two boxes
plugged into the same double socket.
Your tingle was because your equipment is not grounded, and is perfectly normal.
Eiron spake thus:
No, my tingle was because I was holding two cables strung between two
different houses, each grounded at its end. Doesn't seem normal at all
to me.
Most likely the two houses weren't on the same phase of the three
phase supply to the street. Their two grounds could have been doing
very different things voltage-wise. You should always have an
isolation transformer in a connection like this.
d
Don Pearce spake thus:
I seriously doubt that, because then the potential would have been more
like 120 volts, right? I think that's grasping at straws: so far as I
know, PG&E (local electricity dealer) doesn't even supply 3-phase to
residential customers. In fact, not even in come commercial districts. I
owned a small business in Berkeley (print shop) until last year, and I
remember the previous owner telling me about all the headaches he had in
having PG&E put in a 3-phase converter (in an underground vault below
the sidewalk outside). So I know that utility lines don't usually carry
3-phase power, except to large industrial customers.
Why would it be 120V? The voltage would depend on how stiff the ground
is round your way. As for three phase supply, no, individual domestic
properties generally don't get that, but streets certainly do - that
is the efficient way to deliver power.
Could be different where you are,of course.
d
I
What they tend to do is supply the area with a three phase line at
around 11Kv and transform that down and then supply house number one
with phase one, house two with phase two, three with phase three, four
with phase one, five with phase two, house six with phase three and so
on. Its called load balancing between the phases...
If they were each properly "grounded", you would NOT
have seen any voltage differential. BY DEFINITION.
(Or else the two houses were on differen planets. :-)
Not in the parts of the USA where I have lived (up and down
the west coast). They break up the 3 phases back at the main
road and supply only one of the phases to each street (or 2-3
streets depending on the load) It is not economical to run all
3 phases along residential (or even small business) areas.
I would almost bet that at least one of them wasn't really grounded (to the
earth).
Second choice is that high voltage is being conducted directly into the
earth from some kind of unintended connection. A bad thing.
As I understand it, the British ring system is to wire the outlets in a room
in a ring so that each of them has two parallel paths to the point where
power enters the room. As a result, a single high-resistance connection
anywhere in the ring will have almost no effect. That should do a more
reliable job of tying together all the ground connections for the different
pieces of equipment.
Two boxes with 3-wire plugs?
Could you elaborate? I thought a ground loop was due to difference in
potential of the ground connections of 2 different pieces of equipment.
So what do they do when somebody asks for three phase supply? Even a
reasonably small business here in the UK might well do that if their
power needs are significant. The power companies here actually prefer
to supply businesses that way, particularly if they are also careful
about their power factor correction.
Or are zoning laws in the States such that it is not possible to set
up a business in an otherwise residential area?
d
Almost right. The ring actually goes right back to the breaker box,
which is always located where the power enters the house. But the
effect is the same.
d
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