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Author Topic: 2 pair shielded wire termination to 1/8" audio jack... pin config help, Please  (Read 6158 times)

Barry Hans

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I need some help with wiring a cable for a installed signal wire run. I am going to install a 1/8" computer audio jack and cable up to a projector for audio. I have Belden 88723 2 pair shielded wire. I am wondering if I should tie the shield wire to the L- & R- (sleeve) on both ends or only one one end? If connecting one one end only I presume it is on the input (projector) side?
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Joseph D. Macry

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I need some help with wiring a cable for a installed signal wire run. I am going to install a 1/8" computer audio jack and cable up to a projector for audio. I have Belden 88723 2 pair shielded wire. I am wondering if I should tie the shield wire to the L- & R- (sleeve) on both ends or only one one end? If connecting one one end only I presume it is on the input (projector) side?

Tie shield to sleeve on both ends. This is an unbalanced, stereo signal. Lift the ground on either end and neither channel will work. As with all unbalanced runs, try to keep it short.
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Joseph Macry,
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Mac Kerr

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« Reply #2 on: September 08, 2011, 04:16:47 pm »

I need some help

Please go to your profile and change the "Name" field to your real full name as required by the posting rules clearly displayed in the header at the top of the section, and in the Site Rules and Suggestions in the Forum Announcements section, and on the registration page when you registered.

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Brian Ehlers

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Tie shield to sleeve on both ends. This is an unbalanced, stereo signal. Lift the ground on either end and neither channel will work. As with all unbalanced runs, try to keep it short.
However, depending on the internal design of the equipment at each end, and the mains powering each end, the signal ground path might end up carrying some unintended currents -- with undesirable results in either the projected video or amplified audio.

If this is the case, you will need to break the connection with signal transformers.  You could use passive transformers at each end, though I would prefer to use distribution amp, active DI, or something else to actively drive a balanced signal, then put a transformer at the receiving end.  Regardless of how you do it, the objective is to make the bulk of the wire run with a balanced signal and tie the shield of that run to chassis ground only at the transmitting end.
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Hal Bissinger/COMSYSTEC

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Another question would be, if you do go the unbalanced route using 2 pair overall shielded cable, what are you going to do with the second conductor of each twisted pair? They too should be tied to ground.
 
-Hal
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Brad Weber

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I need some help with wiring a cable for a installed signal wire run. I am going to install a 1/8" computer audio jack and cable up to a projector for audio. I have Belden 88723 2 pair shielded wire. I am wondering if I should tie the shield wire to the L- & R- (sleeve) on both ends or only one one end? If connecting one one end only I presume it is on the input (projector) side?

Belden 88723 apparently has two individually shielded, but not individually jacketed, twisted pairs, with an overall jacket but no overall shielding and a single drain wire.  What are you terminating to at the projector end, is it also a 1/8" TRS stereo jack or is it two RCAs or something else?  It seems that could affect what you might do.
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Barry Hans

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I will be terminating the cable to 1/8" trs on both ends. My wording may be wrong in my description. Here is my understanding for the terminations: L+ = Tip, R+= ring and L- & R- tied to sleeve. Should the drain be connected to the sleeve also? One or both ends? I was a bit confused on the shield vs.  drain wire.
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Hal Bissinger/COMSYSTEC

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Belden 88723 apparently has two individually shielded, but not individually jacketed, twisted pairs, with an overall jacket but no overall shielding and a single drain wire.

Yes, I see that now that I looked it up.
 
Should the drain be connected to the sleeve also? One or both ends?
 
The drain wire connects to the shields and is how you connect them. You have L-&R- connected at both ends, I don't think it will matter if you connect the shield at both ends- as long as it's connected at one end.
 
I also think that this is a lot going on to fit in the shell of a 1/8" plug, no?
 
-Hal
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Brad Weber

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I also think that this is a lot going on to fit in the shell of a 1/8" plug, no?
In fact it may be that the only practical option is to just use one of the pairs for tip and ring and tie the drain to the sleeve at either both ends or at the source end only, leaving the second pair unused.
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Barry Hans

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Using one pair for both tip & ring then drain to sleeve on both ends makes a lot of sense. Thanks for the help!
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