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It is possible to get good performance when sending line level or mic level balanced signals down a lengthy piece of CAT5 UTP? I assume that 4 wires would be used... hot wrapped around ground, and cold wrapped around ground.

If this would work, could the remaining four wires be used for a second channel, or would crosstalk be an issue without internal shielding?

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Not really an answer, but we once had an analogue building PA system that we needed to extend to a new part of a building that they didn't run the wires to. We wired CAT5 and RJ45 with a stereo 3.5mm plug and patched it through the networking cabling. It worked fine, but we're talking about a building PA system, not high fidelity ;) –  Mark Henderson Dec 15 '10 at 20:47
    
Interesting question, can someone with mad DIY skillz fill us in please? :) –  Ed J Dec 17 '10 at 12:03

2 Answers 2

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To get adequate performance, you must use a differential amplifier and receiver to reject the electromagnetic noise that the UTP will pick up from the surrounding environment. This is what audio mixers use to reject hum from microphone cables.

alt text

In order for this to work, you would need a circuit at the transmitting end that transmits the audio signal on one conductor, and its inverse on the other. On the receiving end, these two signals would then be fed into V1 and V2 of the diagram above.

For actual circuits that work, look here: http://sound.westhost.com/project87.htm

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Thanks for the reply Robert. This is what I meant by "balanced". I think I will give this a try soon. Thank you for your input. –  Brad Dec 18 '10 at 5:06

Perhaps something like this would do the trick.

InstaSnake PA200 Series

http://www.computercablestore.com/PDF/ETS-PA202F.pdf

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I'm mainly asking for direct wiring applications, but that device is interesting. There is more going on there than simply hooking the wires to the plugs, as even if you use a common ground, you're still short one wire. Anyone have any idea how that works? –  Brad Dec 17 '10 at 18:14
    
@Brad: I am guessing that the InstaSnake device has figured out a way to float the ground, saving one conductor. A device like this relies on the common mode rejection you get from using balanced connections. It will not work with unbalanced connections (it would pick up too much electromagnetic interference from the surrounding environment). –  Robert Harvey Dec 17 '10 at 20:34

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