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How much cable length is too much?
John 31415926
post Jul 19 2012, 07:34
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I just rearranged my home office and the Mac (running iTunes) is now about as far away from the receiver/amp as it can be. It's looking like the only way to connect the Mac to my receiver is to run an audio cable up the wall, through the attic, across the room, back down the opposite wall, and into the audio system ...

... to the tune of about 40 to 50 feet of cable distance.

I think I had a length like this a while back and I vaguely remember getting some hiss, although I don't know for a fact if that was the cable length causing that or something else.

Right now I've got a spool of 18 gauge speaker wire, would that do the job?

I guess it's two questions.

1) How much length is too much to connect a computer to a receiver?

2) What gauge wire is required for such a length?



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greynol
post Jul 19 2012, 08:11
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Such a cable, if only running a line-level signal will probably need to be shielded. As such I don't think speaker wire will do the trick, regardless of the gauge.

Have you considered going wireless using something like an AirPort Express or Squeezebox? These days there are a lot more solutions than there used to be.


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John 31415926
post Jul 19 2012, 08:16
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QUOTE (greynol @ Jul 19 2012, 00:11) *
Such a cable, if only running a line-level signal will probably need to be shielded. As such I don't think speaker wire will do the trick, regardless of the gauge.

Have you considered going wireless using something like an AirPort Express or Squeezebox? These days there are a lot more solutions than there used to be.


Thank you for the reply.

I know nothing about AirPort ... have only heard the name. I'll have to google it, learn what it does, and see if it does the job for me. I've never heard of Squeezebox at all.

Are these wireless solutions of high audio quality? I don't know much about hardware, but I inherited a very substantial Kenwood stereo system and the sound system never ceases to amaze me. I wonder if I would get the same quality going wireless from across the room as I would from the CD player that sits right there on top of the receiver?


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probedb
post Jul 19 2012, 08:38
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Why wouldn't you get the same quality?
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dhromed
post Jul 19 2012, 10:02
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QUOTE
Are these wireless solutions of high audio quality?


Airport is a wifi station. Data is transmitted digitally and therefore does not influence sound quality.
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2Bdecided
post Jul 19 2012, 10:30
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QUOTE (dhromed @ Jul 19 2012, 10:02) *
QUOTE
Are these wireless solutions of high audio quality?


Airport is a wifi station. Data is transmitted digitally and therefore does not influence sound quality.

32kbps mp3 is digital wink.gif

but both the suggested solutions allow lossless, so no quality loss.

Assuming the OP likes the existing (via a Mac) interface, and doesn't want to replace their (probably) non-Airport receiver, I'd try a long, reasonably well screened cable. Beware of earth loops, different phases of mains wiring at the two outlets, and running the wire close to (especially in parallel with) other cables (it can pick up interference this way). If the computer has a digital output, and the receiver has a digital input, use that if it's SPDIF (coaxial) - I have no experience of using TOSlink (optical) over a long distance.

The choice of wire matters, but it doesn't need to be expensive. I ran SPDIF over 50m (164ft) of the worse coaxial cable imaginable, and it worked fine except when I switched the florescent lights on.

Hope this helps.

Cheers,
David.
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dhromed
post Jul 19 2012, 11:47
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QUOTE (2Bdecided @ Jul 19 2012, 11:30) *
32kbps mp3 is digital wink.gif


Yes but you can be sure your crystal-clear artifacts will not suffer any degradation in transit. emot-pseudo.gif
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botface
post Jul 19 2012, 12:03
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QUOTE (John 31415926 @ Jul 19 2012, 06:34) *
I just rearranged my home office and the Mac (running iTunes) is now about as far away from the receiver/amp as it can be. It's looking like the only way to connect the Mac to my receiver is to run an audio cable up the wall, through the attic, across the room, back down the opposite wall, and into the audio system ...

... to the tune of about 40 to 50 feet of cable distance.

I think I had a length like this a while back and I vaguely remember getting some hiss, although I don't know for a fact if that was the cable length causing that or something else.

Right now I've got a spool of 18 gauge speaker wire, would that do the job?

I guess it's two questions.

1) How much length is too much to connect a computer to a receiver?

2) What gauge wire is required for such a length?

I run a cable from my PC to an amplifier in a different room via the roof space. Overall it's about 70ft. I took no care at all about avoiding other cables in routing it and there is a very faint hum on 1 channel but you can't hear it unless you put your ear right up against the speaker. I used microphone cable. Not because it has any special audio qualities but because a single mic cable is able to handle separate left and right channels as it contains 2 signal leads inside a shared screen. It is slightly fiddly to solder up as you need to split the screen to "share" it between 2 plugs (I assume your receiver uses RCA plugs) so you might prefer to use conventional 2 channel cable. I'd say try it and see. It's much cheaper than any wireless solution so you've not got much to lose if it doesn't work out
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uart
post Jul 19 2012, 12:31
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QUOTE (John 31415926 @ Jul 18 2012, 23:34) *
I just rearranged my home office and the Mac (running iTunes) is now about as far away from the receiver/amp as it can be. It's looking like the only way to connect the Mac to my receiver is to run an audio cable up the wall, through the attic, across the room, back down the opposite wall, and into the audio system ...

... to the tune of about 40 to 50 feet of cable distance.

I think I had a length like this a while back and I vaguely remember getting some hiss, although I don't know for a fact if that was the cable length causing that or something else.

Right now I've got a spool of 18 gauge speaker wire, would that do the job?

I guess it's two questions.

1) How much length is too much to connect a computer to a receiver?

2) What gauge wire is required for such a length?


Shielding is far more important than the wire gauge here John. Use a well shielded cable, not speaker wire.

Apart from shielding, the other really important issue here (as David already mentioned) is grounds loops. Ground loops can allow relatively large currents to circulate in the ground or shield wires, and can result in significant hum. If you experience this (hum with a direct analog line connection) then one way to test if it's a ground loop issue is to also run an extension power cable from the computer to the receiver. So that the receiver (and everything thing electrically connected to it!) is getting its mains power directly from the same power board as the computer. This gives a single ground point. I've solved several ground loop issues in the past using this technique.

This post has been edited by uart: Jul 19 2012, 12:34
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pdq
post Jul 19 2012, 12:52
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You should also consider a solution like this. It allows you to transmit the stereo audio over inexpensive, unshielded cat5 cable over long distances. Because the signal is carried over balanced rather than unbalanced cable, it is much less suceptible to picking up noise, and ground loop problems are eliminated.
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greynol
post Jul 19 2012, 14:38
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QUOTE (2Bdecided @ Jul 19 2012, 02:30) *
Assuming the OP likes the existing (via a Mac) interface, and doesn't want to replace their (probably) non-Airport receiver

It's important to note that the word Express was unfortunately dropped from the discussion. An Apple AirPort and an AirPort Express are different products. The latter allows one to add wireless functionality to a receiver rather than require one to replace a receiver that does not have wireless functionality.


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greynol
post Jul 19 2012, 14:45
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QUOTE (botface @ Jul 19 2012, 04:03) *
I used microphone cable. Not because it has any special audio qualities but because a single mic cable is able to handle separate left and right channels as it contains 2 signal leads inside a shared screen.

Not a bad idea except for the possible dramatic increase in stereo cross-talk.

I'm tempted to use that to reduce the number of cords running across the floor to and from the pedal board in my guitar rig but instead of coupling left and right, I'd be coupling ins and outs which could lead to feedback problems.

This post has been edited by greynol: Jul 19 2012, 14:48


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punkrockdude
post Jul 19 2012, 16:07
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QUOTE (greynol @ Jul 19 2012, 15:45) *
I'm tempted to use that to reduce the number of cords running across the floor to and from the pedal board in my guitar rig but instead of coupling left and right, I'd be coupling ins and outs which could lead to feedback problems.
Can two wires seperated from each others by plastic coating inside a cable cause feedback? Sounds interesting. Can you explain the details, please? Regards.
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greynol
post Jul 19 2012, 16:14
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Think of the insulation as a dielectric inside a capacitor and the wires themselves as the plates. The cable is literally a capacitor directly coupling the two connection pairs (L out -> L in, R out -> R in; or any two of the following: pedal board FX send 1 -> guitar amp input, guitar amp send -> pedal board FX return, pedal board FX send 2 -> guitar amp return/power amp in).

This post has been edited by greynol: Jul 19 2012, 16:34


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uart
post Jul 19 2012, 17:49
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The roll of mic cable I've got here has two separate co-ax cores (conductor with coax surrounding return) together enclosed in one overall outer screen. I'm not sure if all mic cables are constructed like this, but it should keep the crosstalk pretty low. Personally I don't find small amounts of crosstalk a very annoying (or even noticeable) artifact, at least not for the material I listen to. smile.gif

This post has been edited by uart: Jul 19 2012, 17:50
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Arnold B. Kruege...
post Jul 19 2012, 22:18
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QUOTE (uart @ Jul 19 2012, 12:49) *
The roll of mic cable I've got here has two separate co-ax cores (conductor with coax surrounding return) together enclosed in one overall outer screen.


Sounds like twinax to me, not any regular mic cable that I've ever seen.

QUOTE
I'm not sure if all mic cables are constructed like this,


None are, because the dual shielded wires are dysfunctional for mics.


QUOTE
but it should keep the crosstalk pretty low.



Crosstalk is rarely an issue.

QUOTE
Personally I don't find small amounts of crosstalk a very annoying (or even noticeable) artifact, at least not for the material I listen to. smile.gif


Musical recordings are supposed to be stereo, not dual mono.
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Arnold B. Kruege...
post Jul 19 2012, 22:21
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QUOTE (punkrockdude @ Jul 19 2012, 11:07) *
QUOTE (greynol @ Jul 19 2012, 15:45) *
I'm tempted to use that to reduce the number of cords running across the floor to and from the pedal board in my guitar rig but instead of coupling left and right, I'd be coupling ins and outs which could lead to feedback problems.


Can two wires seperated from each others by plastic coating inside a cable cause feedback? Sounds interesting. Can you explain the details, please? Regards.


It is common practice to put mic input lines (very sensitive) and line-level outputs for driving monitor amplifiers on stage (far higher signal voltages) into the same cable, provided each connection is a shielded pair and balanced inputs and outputs are involved for at least for the mic lines.
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greynol
post Jul 19 2012, 22:31
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QUOTE (Arnold B. Krueger @ Jul 19 2012, 14:21) *
It is common practice to put mic input lines (very sensitive) and line-level outputs for driving monitor amplifiers on stage (far higher signal voltages) into the same cable, provided each connection is a shielded pair and balanced inputs and outputs are involved for at least for the mic lines.

Of course we weren't talking about each individual connection consisting of a pair of conductors sharing a common shield carrying a differential signal; rather, we were talking about using the two conductors for two separate connections with the shield being shared as a common ground (i.e. each of the connections is single-ended).

This post has been edited by greynol: Jul 19 2012, 23:34


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