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  #1  
Old 09-21-2017, 09:16 AM
Bill Boyd's Avatar
Bill Boyd Bill Boyd is offline
 
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Default Insulalting washers

I'm planning on mounting my 4 each headphone and mic jacks in aluminum panels that will free-float (electrically) in my fiberglass overhead console. That is, without insulating shoulder washers, they will be "grounded" to each other in the mounting panel, but not to airframe ground.

That being the case, do I need shoulder washers to insulate them from each other, or are they okay sharing a common local, floating connection of the outer shells?
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  #2  
Old 09-21-2017, 09:55 AM
rv7charlie rv7charlie is offline
 
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If I were building, I'd probably not worry about it. The 'danger' of local grounding is usually the risk of getting another device's noisy, high current ground return path mixed into the low level audio return path.

As long as you design for ease of future access, you can always, at a later date, remove one jack, bore out the hole for the insulating washer, and add it, if needed.

Or, just make your mounting plate from a scrap piece of PC board with the copper cladding removed.
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  #3  
Old 09-21-2017, 10:02 AM
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Bill Boyd Bill Boyd is offline
 
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Default Thanks, Charlie.

I suspected as much but wanted to make sure. There'll be nothing sharing a connection to this little rectangle of aluminum besides the jacks for the other passenger. I will leave off the insulating washers from the Spruce order.

Hey, 8 x 98 cents is $7.94 or thereabouts
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  #4  
Old 09-21-2017, 10:54 AM
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If you are using the carbon fiber overhead and not an actual fiberglass one, then you need the washers. Carbon fiber conducts electricity.
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  #5  
Old 09-21-2017, 11:14 AM
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Bill Boyd Bill Boyd is offline
 
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I made a fiberglass overhead. The jacks will mount in an aluminum insert panel in the overhead, which panel will only be connected to the airframe or avionics ground via the lengths of shielded wire connected to the jacks. Therefore the mic and phone jack outer rings would be bonded to each other via this aluminum, but no ground loop via a local bond to airframe ground, as I see it.
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  #6  
Old 09-21-2017, 11:44 AM
BobTurner BobTurner is offline
 
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Location: Livermore, CA
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Default Other opinion

I think the odds are pretty good that you won't need the insulating washers, especially if you don't mind a little noise. But if you do need to retrofit, you'll need to remove and replace every wire to every jack, to get them thru the washers. For $8 I'd do it now. (Ounce of prevention worth a pound of cure.)
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  #7  
Old 09-21-2017, 11:58 AM
HarryL HarryL is offline
 
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As the washers go on the threaded portion of the mic and tells sockets you don't need to de-solder to install them later.
Some audio systems have floating (transformer-coupled) phones outputs, so by not using insulating washers you have the potential to mix mic noise onto the isolated phones system or vice-versa when the sockets share a common metal mounting plate. For the sake of a few $ I would install them and not take the risk.
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  #8  
Old 09-21-2017, 12:03 PM
Mich48041 Mich48041 is offline
 
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Compromise
Only insulate the mic jacks. The mic signals get amplified along with any noise. The earphone audio has already been amplified, so it is not as vulnerable to noise. Aircraft Spruce part numbers 04-00975 and 04-00976.
Total cost $4. Labor to add insulating washers later will be worth more than $4.
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  #9  
Old 09-21-2017, 12:26 PM
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Ironflight Ironflight is offline
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Usually, when I buy jacks, they come with a set of insulating washers anyway.....and if they do, why not use them?
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  #10  
Old 09-21-2017, 12:38 PM
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DanH DanH is offline
 
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Install the washers.

Perhaps it would be best if you don't tell Otis


V
V
V
V
V

(I'm kidding Otis, really!)
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