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04-26-2014, 05:37 PM
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Join Date: Jun 2005
Location: Raleigh, North Carolina
Posts: 1,128
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Looping ground NOT ground loop
In the process of wiring stereo headphone /microphone jacks. Wiring diagram shows all shielding tied together at the intercom and connected to ground pin in plug. Now the barrel / mounting nut of the jack has continuity with the shielding. If I mount it to the aluminum panel won't that cause the dreaded ground loop?
Should I isolate the jacks on a non- conductive surface? 
Any advice will be greatly appreciated .
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Tom Norwood
Classic "Short Tail 6A N822PM
TMX-O360. Phase 1
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04-26-2014, 06:06 PM
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Join Date: Jun 2006
Location: Vero Beach, FL
Posts: 880
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Tom, you need to get the fiber washers that isolate your audio jacks. There are two for each jack, one side has a shoulder that keeps the barrel centered in the hole so that it can't touch the aluminum panel. Depending on where you got your audio jacks, they sometimes will be supplied with these washers. If not, they can be obtained from many of the avionics shops such as Aerotronics or Stein.
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04-26-2014, 07:08 PM
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Join Date: Jun 2005
Location: Raleigh, North Carolina
Posts: 1,128
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Brain Fart
Aw thanks Pat, I can sleep now. Trying so hard to avoid interference in my audio I didn't even think of those insulators. I bought the jacks I have from ACS. I see now that they have the insulators on their site and just ordered some.
Thanks again for getting me back on the right track Pat. 
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Tom Norwood
Classic "Short Tail 6A N822PM
TMX-O360. Phase 1
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04-26-2014, 07:38 PM
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Join Date: Apr 2012
Location: West Fargo, ND
Posts: 1,073
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Would be much better if the jacks simply came the fiber washers, or at least said in big bold letters that you need to also buy the fiber washers... I too learned this the hard way.
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Derek Hoeschen
EAA Tech Counselor
RV-9A #92103 - N803DK
G3X, Superior XO-320, Dual Pmags, Catto 3B
www.mykitlog.com/dbro172/
1974 Bellanca Super Viking - N16AW - Flying
RV-8 #83565 - N184DK - building
1968 Mooney M20C - N6801N - Sold
1956 C-182 - N744W - Sold
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04-26-2014, 08:16 PM
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Join Date: Dec 2008
Location: Big Sandy, WY
Posts: 2,567
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The spruce shoulder washers have a really narrow shoulder so don't drill out the hole to 1/2 inch. Its more like 15/32.
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Actual repeat offender.
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04-26-2014, 08:17 PM
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Join Date: Jul 2010
Location: Marietta, GA (KCZL)
Posts: 308
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I learned this the hard way too. I bought the '4 place jack pack' from spruce and it seemed (at least to me) like maybe only the mic was supposed to be insulated off metal. I had terrible engine noise and I bought some nylon washers from hardware store and made sure no jacks were touching metal and now its super quiet and awesome!
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Brian Unrein
RV10 N42BU 900+ hours!
First flight 6-16-12
https://N42BU.com 
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04-26-2014, 10:28 PM
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Senior Curmudgeon
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 15,408
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Mike Starkey
VAF 909
Rv-10, N210LM.
Flying as of 12/4/2010
Phase 1 done, 2/4/2011
Sold after 240+ wonderful hours of flight.
"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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04-27-2014, 05:12 AM
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Join Date: Jun 2005
Location: Raleigh, North Carolina
Posts: 1,128
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Quote:
Originally Posted by aerhed
The spruce shoulder washers have a really narrow shoulder so don't drill out the hole to 1/2 inch. Its more like 15/32.
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Thank you, good tip & will do.
Probably should have bought from Stein but I hate to bother him with tiny orders, but get the big $$$ stuff from him. ACS is just so darn easy and fast for the little "need it right away" things. 
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Tom Norwood
Classic "Short Tail 6A N822PM
TMX-O360. Phase 1
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