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Question re: splitting audio output

 
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shoemkr
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PostPosted: Fri Oct 21, 2011 7:35 am    Post subject: Question re: splitting audio output Reply with quote

Hello all! I've run across an "interesting" problem with my Mac mini (Early 2009), specifically when I attempt to split the audio output to both a pair of computer speakers and to my TV.

Using this splitter cable, plugged into my Mac mini's audio out/speaker port, whenever I have both my computers speakers and the audio cable that goes to my TV plugged in, there is static on the computer speakers (though none on the TV). However, if I unplug the TV audio cable from the splitter cable, but still leave the splitter cable in place, the static on the computer speakers goes away. Any idea why the adding of the audio cable going to the TV would produce static on the computer speakers? (So you'll know, I've tried multiple splitter cables and the static still exists when both the speakers and TV audio are plugged into it.)

Any input/advice on this situation would be much appreciated. Thank you!

Joel
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Fred76
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PostPosted: Fri Oct 21, 2011 8:13 am    Post subject: Reply with quote

Try plugging in your TV and/or (if applicable) active speakers without the ground prong connected to 'earth'. If the static goes away, your problem is a ground loop between the active speakers and your TV.
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shoemkr
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PostPosted: Fri Oct 21, 2011 8:43 am    Post subject: Reply with quote

I think I'm somewhat following what you're saying, Fred, and - at least based on my limited knowledge - what you suppose may be happening may indeed be the case. Perhaps a few more details about my setup may help us find out for sure (please read on).

From the splitter audio cable, there is a 6' audio cable that goes to a VGA/3.5mm audio wall plate, which then has a 75' audio cable that runs around (through the wall) to the backside of another VGA/audio wall plate of the same type, which then has 3' VGA and 3' 3.5mm audio cables coming out the front of it and going into the proper inputs on my TV (a Sony 55" LCD). There are no external speakers directly connected to the TV, rather only speakers connected through a stereo unit that it connected to the TV. (I don't know if it matters, but the stereo-connected speakers are either sitting on the floor or are surround sound speakers mounted on the wall, while the smaller computer speakers are sitting on my desk, but the computer speaker woofer is sitting on the floor.) Note that the static problem occurs on the computer speaker end even if the TV and stereo are off.

Does that help clarify where/what the problem may be? Thank you again for your help!
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geeji
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PostPosted: Sat Oct 22, 2011 2:17 am    Post subject: Reply with quote

It looks like a ground loop. If the problem disappears on the computer when the TV audio input is unplugged, it definitely is.
Using a ground isolator like PAC SNI-1/3.5 3.5mm Ground Loop Isolator should cure the problem.
Put it serially with the computer connection; if it does not work, try it with the Mini connection or the TV connection.

Too bad you cannot connect your TV and your computer using a (splitted) TosLink optical input, that would have avoided this problem...
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philiparcario
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PostPosted: Sat Oct 22, 2011 5:35 am    Post subject: Reply with quote

one other option is


http://www.behringer.com/EN/Products/UCA202.aspx


use it with the tv
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shoemkr
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PostPosted: Sat Oct 22, 2011 9:33 pm    Post subject: Reply with quote

Thank you all for your informative and complete answers. A ground loop it is (hey, I've learned something new today). Seems like the ground loop isolater is the way to go (based on cost as well). I'll give that a shot and see how it goes.

Thanks again!
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shoemkr
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PostPosted: Mon Dec 12, 2011 6:22 pm    Post subject: Reply with quote

FYI: Finally bought one of these and it appears to have resolved the ground loop issue. Just added the isolator in-between the audio cable coming from the TV and the splitter and the static is completely gone from the computer speakers. Thanks again for your help!

Joel
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Bradley in DC
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PostPosted: Sun Jan 15, 2012 5:34 pm    Post subject: Reply with quote

Not to highjack the thread, but I'm having a similar hiss problem. No audio splitter or anything, but there is a loud hiss on the TV. It's an older one with a converter box. The hiss only comes on when the cable is attached to the converter box. Very open to suggestions!
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