Matronics Email Lists :: View topic - Installing Audio Jacks

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

Installing Audio Jacks

Matronics Email Lists Forum Index -> AeroElectric-List

View previous topic :: View next topic

Author Message

trigo(at)mail.telepac.pt
Guest

Posted: Sun Oct 26, 2008 11:28 am Post subject: Installing Audio Jacks

I am installing the Intercom in my RV and I remember reading in this forum that, when installing the audio jacks on the panel or any other aluminium surface of the cockpit, one shall isolate the jacks from the metal surface with plastic or rubber insulating washers.  

However, in the Flightcom instructions they only recommend (and include washers to) isolation of the Microphone jack and not in the Headphone jack.   

They even show in the schematic drawing the Headphone jack locally grounded.  

   

Is this correct? If yes, why?  

   

Carlos  

   

       [quote][b]

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

nuckolls.bob(at)cox.net
Guest

Posted: Sun Oct 26, 2008 12:26 pm Post subject: Installing Audio Jacks

At 07:25 PM 10/26/2008 +0000, you wrote:



 	  Quote: 	
		  I am installing the Intercom in my RV and I remember reading in this forum 

that, when installing the audio jacks on the panel or any other aluminium 

surface of the cockpit, one shall isolate the jacks from the metal surface 

with plastic or rubber insulating washers.



However, in the Flightcom instructions they only recommend (and include 

washers to) isolation of the Microphone jack and not in the Headphone jack.



They even show in the schematic drawing the Headphone jack locally grounded.



Is this correct? If yes, why?


	


  It's a good idea if not a necessary thing to isolate

  small signal systems from airframe ground . . .



   See

http://aeroelectric.com/articles/Rev11/18Audio_R11.pdf





        Bob . . .



        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

        ----------------------------------------

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

ceengland(at)bellsouth.ne
Guest

Posted: Sun Oct 26, 2008 12:49 pm Post subject: Installing Audio Jacks

Carlos Trigo wrote:

 	  Quote: 	
		  

 I am installing the Intercom in my RV and I remember reading in this 

 forum that, when installing the audio jacks on the panel or any other 

 aluminium surface of the cockpit, one shall isolate the jacks from the 

 metal surface with plastic or rubber insulating washers.



 However, in the Flightcom instructions they only recommend (and 

 include washers to) isolation of the Microphone jack and not in the 

 Headphone jack.



 They even show in the schematic drawing the Headphone jack locally 

 grounded.



  



 Is this correct? If yes, why?



  



 Carlos




	


The non-physics-based answer is probably: ground loop induced noise on 

the input (mic) side gets amplified; the output side is less likely to 

cause problems.

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

trigo(at)mail.telepac.pt
Guest

Posted: Sun Oct 26, 2008 12:56 pm Post subject: Installing Audio Jacks

Bob  

   

I really didn’t find anything about my question in the link you provided, although it is your book’s chapter about Audio Systems.  

   

Can you please be more specific about what you think about not insulating the Headphone jack?  

And if I isolate it, to where exactly should I connect the ground lug of the Headphone jack?  

   

Carlos  

   

   

[quote] --

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

nuckolls.bob(at)cox.net
Guest

Posted: Mon Oct 27, 2008 5:56 am Post subject: Installing Audio Jacks

At 08:53 PM 10/26/2008 +0000, you wrote:



 	  Quote: 	
		  Bob



I really didn t find anything about my question in the link you provided, 

although it is your book s chapter about Audio Systems.


	


  My apologies, I thought I'd touched on signal grounds

  in that chapter . . .



  In complex machines where there is a mix of power (100 ma and

  up) and signal systems (milliamperes and down) it is useful to

  make some effort to isolate these systems from each other as

  much as practical.



  This starts with single point grounding so that no potential

  victim (in this case headphones) has it's desired signal (ATC

  talking to you) polluted with undesired signals (alternator

  whine) because the power and signal ground paths are shared

  along some portion of the airframe.



  The underlying thought here is that "ground is not ground"

  for all systems when you simply tie the ground wires to the

  vehicle structure. At Cessna way back when, we simply tied

  mic and headset jacks to airframe ground at the lower edge

  of the panel. As loads in the airplane went up and generators

  were replaced with alternators, there was the occasional situation

  where alternator noise was heard by folks at the other end of

  your transmission . . . or you could hear alternator whine

  in your headsets.



  NONE of the noise mitigating techniques (isolation washers,

  single point grounds, shielded wires, etc) are absolute

  guarantees against having to wrestle with a noise issue. These

  are easy to accomplish, prophylactic measures that have been

  shown to be useful in the past and when implemented in total

  one can expect eliminating 99.9% of all potential noise

  propagation paths . . . therefore we recommend that they be

  implemented as standard practice.



  Bob . . .



[quote]



Can you please be more specific about what you think about not insulating 

the Headphone jack?



And if I isolate it, to where exactly should I connect the ground lug of 

the Headphone jack?



Carlos



 > --

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

trigo(at)mail.telepac.pt
Guest

Posted: Mon Oct 27, 2008 2:42 pm Post subject: Installing Audio Jacks

Many thanks Bob  

Now I got the whole picture!! Obviously I will isolate the headphone jacks as well…  

   

Now, isolating the headphone jacks from the airframe, where should I connect its ground lugs to?   

Shall I run a dedicated wire from each jack ground lug?  

Shall this wire go to the firewall single point ground, or to pin 13 (mic return) or pin 1 (ground) of the Intercom?  

   

By the way (and forgive me for asking so many questions), since I am using shielded wire to connect Mic and Headphone jacks to the Intercom, on which side should I connect the shield mesh to ground, the jack or the Intercom?  

   

Carlos  

   

   

[quote] --

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

nuckolls.bob(at)cox.net
Guest

Posted: Mon Oct 27, 2008 4:20 pm Post subject: Installing Audio Jacks

At 10:38 PM 10/27/2008 +0000, you wrote:



 	  Quote: 	
		  Many thanks Bob



Now I got the whole picture!! Obviously I will isolate the headphone jacks 

as well&



Now, isolating the headphone jacks from the airframe, where should I 

connect its ground lugs to?


	


   back to ground at the same device that drives the

   headphones (iso amp, intercom?). See . . .



http://www.aeroelectric.com/DIY/Audio_Isolation_Amplifier.pdf



    . . . in every schematic, I show the signal ground for EACH

    headset and EACH microphone jack returned to ground on the

    device that gets the signal wires.

 	  Quote: 	
		  Shall I run a dedicated wire from each jack ground lug?


	


    For headsets, I use single shielded (shielded pair for

    stereo) and often use the shield itself as the ground

    return. This way all the conductors stay together. Mic

    jacks can be a shielded trio (or shielded pair with

    ground being the signal ground for the mic jack. Either

    way works fine.

 	  Quote: 	
		  Shall this wire go to the firewall single point ground, or to pin 13 (mic 

return) or pin 1 (ground) of the Intercom?


	


    To the device that needs or delivers signals to the other

    end.



    The next audio isolation amp under design will have LOTS

    of extra ground pins to accommodate minimum-risk wiring

    techniques without having to splice a half dozen grounds

    before dropping them into a single pin. These grounds

    never go to an airframe ground like g1 thru g5 unless

    specifically called out on the diagram.



    Bob . . .

 	  Quote: 	
		  



By the way (and forgive me for asking so many questions), since I am using 

shielded wire to connect Mic and Headphone jacks to the Intercom, on which 

side should I connect the shield mesh to ground, the jack or the Intercom?


	


    At the intercom end only unless you're using that

    ground as part of the signal path.



    Bob . . .

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

Display posts from previous:

	Matronics Email Lists Forum Index -> AeroElectric-List	All times are GMT - 8 Hours
Page 1 of 1

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum