Unshielded twisted pair phone wire for carrying audio signal?

J

JamesO

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I need to carry a stereo audio signal from the 3.5mm female jack on a common PC sound card to self-powered PC speakers about a hundred feet away. Does anyone see any problem with using unshielded twisted pair phone cable (the stuff one buys at Home Depot to do residential analog telephone wiring) for this purpose? To plug in to the sound card and the PC speakers, I have a short audio cable (stereo male miniplug at both ends) which I can snip in the middle and splice to the telephone cable, giving me an audio miniplug on either end of the phone cable.

Do y'all expect phone cable to be a suitable conductor at this distance? Keep in mind that the telephone cable contains four pairs of conductors, so I have the option of connecting pairs of bare wire ends together to effectively make six of the eight conductors act as three conductors, if that reduction of resistance is called for.
 
whatchel1

whatchel1

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Sep 30, 2006
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Bad idea

It would be a bad idea. The phone cable will not work very well. The crosstalk it could pick up will not be good. It's impedance is wrong for audio. There is a good chance it will pick up low frequency hum. CAT 5 might work but it would be better to use shielded twisted pair cable.
 
Ilya

Ilya

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Welcome to the forum, JamesO! :wave

I think you would be much better off buying a 3.5mm Stereo Extension cable.
 
J

JamesO

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I should mentioned it's for voice only

Mucho gracias for the input. I should have mentioned that this is a voice-only application, for my use only (no need to impress anyone) so sound quality isn't important. As long as I can hear what's being said, I'm good. Aside from hum (doesn't twisted pair prevent that? I don't know, just asking), what should be the result of inappropriate impedance? Also, would a balun be feasible to solve the impedance problem?
 
W

wonko

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Jun 12, 2007
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Also, would a balun be feasible to solve the impedance problem?

Yes a balun would work fine, but the pre-made ones are expensive. It would be a lot cheaper to buy a good shielded audio extension. Monoprice has a 100-foot extension for $15.47.
 
J

JamesO

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Thanks

Yow, that is an excellent price for a 100-ft cable. Thanks a mil for turning me on to monoline!
 
Claude Greiner

Claude Greiner

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Sep 8, 2003
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You can try it and see if it works!

Heck, I got a loud speaker on my phone system which is running off of a 70 volt amplifier running on Cat5 and it sounds just fine!
 
KKlare

KKlare

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Nov 18, 2003
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Cat 5 is better than Cat 3 because there are more twists per inch, Cat 6 is better yet. You will still want the heaviest gauge you can get, say 22 or 24 rather than 26 or else the lowest frequencies will be resistively attenuated.

A balun (balanced-unbalanced) transformer helps match the source of say 50 to 75 ohms to the line pair of 100 to 125 ohms and back again at the other end. DC-wise, it will look like a short so check what loads can be used. Reflections can be a problem for long runs, too. This was a bigger problem with twin-lead (300 ohm) to coax at 75 ohm, where 2 turns to 1 through a magnetic core made the match and fixed the balun. Some audio sources are more like 5 to 50 kilo-ohms.

-Ken
 
Lord_Vader

Lord_Vader

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Aug 17, 2007
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I used cat 5 to carry audio (line) before. I used to work in a building where I couldn't get radio reception in my office. I cut a cat 5 patch cable in half and spliced 1 pair to each positive and negative leads on an RCA cable. ( I cut the RCA cable in half also. )

I then placed a radio tuner in a window office and connected one end to the line (pre-amp) out on the tuner and the other end to the line in on an amplifier in my office.

tuner -> RCA/CAT5 splice cable -> spare wall jack -> commroom -> patch panel -> spare wall jack in my office -> RCA/CAT5 splice -> amp

Worked great, even through the patch panel in the comm room. The only downside was that I had to go to the remote office to change channels. :)

Edit: I also did a coax run once also. That worked well too.
 

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