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Found it!

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dan(at)azshowersolutions.
Guest

Posted: Mon May 28, 2012 11:44 am Post subject: Found it!

After tracing wires, staring at the Z-16 schematic while going cross-eyed for some time now..I finally found my alternator whine. I thought for sure it was the bridge rectifier I used between the Main and E-buss because when I turned the E-buss on the whine went away. This morning I was doing quite a bit of troubleshooting and happened to try something I somehow overlooked. I turned off my Garmin 396 which has the audio connected to my P-1000 intercom. I think I had done it without the engine running, but today I tried it at idle...and magic happened with no hum at all. I pulled the audio wire from the 396 and started everything up and sure enough, that was it. So now I'm guessing a filter is in order between the 396 and the intercom?  I started searching the net and came up with the PAC RCA Filter  SNI-1/3.5

I'm betting Bob and Company has something already designed and if so it would be greatly appreciated if I could get the schematic and or instructions. I don't mind building it but if there is an easy go-to at low cost that would be good too. 

Bob, I ordered your shottkey diode this week in an effort to make this fix. If you have not sent it yet can I cancel order?

Thank You all for the help you consistently provide,

Dan B

Mesa, AZ



 [quote][b]

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Tue May 29, 2012 5:28 am Post subject: Re: Found it!

Dan,



And you don't think this indicates a problem with the Garmin 396?



Swap units and see (or have it checked) before adding filters.

_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

user9253

Joined: 28 Mar 2008
Posts: 1920
Location: Riley TWP Michigan

Posted: Tue May 29, 2012 5:30 am Post subject: Re: Found it!

Dan B,

The avionics package for my RV-12 came with a ground loop isolator that is connected in series with the Garmin 496 audio output.  The instructions say to use the isolator if XM weather option is installed.  I found a similar looking device on Amazon:

http://www.amazon.com/GROUND-LOOP-ISOLATOR-3-5-APPLICATIONS/dp/B001EAQTRI

Perhaps this is the same device that you found.

Joe

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Tue May 29, 2012 8:57 am Post subject: Found it!

At 02:40 PM 5/28/2012, you wrote:

After tracing wires, staring at the Z-16 schematic while going 

cross-eyed for some time now...I finally found my alternator whine. I 

thought for sure it was the bridge rectifier I used between the Main 

and E-buss because when I turned the E-buss on the whine went away. 

This morning I was doing quite a bit of troubleshooting and happened 

to try something I somehow overlooked. I turned off my Garmin 396 

which has the audio connected to my P-1000 intercom. I think I had 

done it without the engine running, but today I tried it at 

idle...and magic happened with no hum at all. I pulled the audio wire 

from the 396 and started everything up and sure enough, that was it. 

So now I'm guessing a filter is in order between the 396 and the 

intercom?  I started searching the net and came up with the PAC RCA 

Filter SNI-1/3.5



   Filter for what line? Refresh my memory. The pitch

   of the whine changed with engine RPM? Can you run

   the GARMIN from it's own battery supply and still

   have the whine? Does the whine go up and down in

   volume with any of the system volume controls but

   not others?



I'm betting Bob and Company has something already designed and if so 

it would be greatly appreciated if I could get the schematic and or 

instructions. I don't mind building it but if there is an easy go-to 

at low cost that would be good too.



   I'm still not clear as to why you would have the

   noise when the e-bus is powered through the normal

   feed path but goes away when you close the e-bus

   alternate feed. But knowing that it is associated

   with Garmin ops is helpful.



Bob, I ordered your shottkey diode this week in an effort to make 

this fix. If you have not sent it yet can I cancel order?



   Sure.



   Bob . . .

dan(at)azshowersolutions.
Guest

Posted: Tue May 29, 2012 9:18 am Post subject: Found it!

 	  Quote: 	
		          

Dan B,

The avionics package for my RV-12 came with a ground loop isolator that is connected in series with the Garmin 496 audio output.  The instructions say to use the isolator if XM weather option is installed.  I found a similar looking device on Amazon:

http://www.amazon.com/GROUND-LOOP-ISOLATOR-3-5-APPLICATIONS/dp/B001EAQTRI

Perhaps this is the same device that you found.

Joe

Joe, Yes the one you show on Amazon is the one I ran across. I spoke with one other guy (after I found disconnecting the 396 audio out killed the noise) and he indicated he had the same problem with the 396. Interesting that Van's now sends a filter along.

Dan

--------

Joe Gores





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=374162#374162



ator?AeroElectric-List" target="_blank">http://www.matronics.com/Navigato=               - MATRONICS WEB FORUMS=   --> 



 

 

 	


   

 [quote][b]

tomrv4(at)me.com
Guest

Posted: Tue May 29, 2012 9:19 am Post subject: Found it!

I also had a radio noise problem that I finally traced to the audio out line on my 396. It is installed in my panel in an Air Gizmo mount. Turns out the audio out wire was kinking against the back of the mount when I'd stick the unit in. 



I cut away some of the plastic mount right behind the audio out plug, which alleviated the kinking and stopped the radio interference...



Tom



On May 29, 2012, at 8:28 AM, "Eric M. Jones" <emjones(at)charter.net> wrote:



 	  Quote: 	
		   

 

 Dan,

 

 And you don't think this indicates a problem with the Garmin 396?

 

 Swap units and see (or have it checked) before adding filters.

 

 --------

 Eric M. Jones

 www.PerihelionDesign.com

 113 Brentwood Drive

 Southbridge, MA 01550

 (508) 764-2072

 emjones(at)charter.net

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=374160#374160

dan(at)azshowersolutions.
Guest

Posted: Tue May 29, 2012 9:21 am Post subject: Found it!

Eric, I'm not sure yet if my Garmin has a problem or this is an inherent issue with these units. The information I have gathered to date lends itself to the later. 

Dan



[quote]        From: Eric M. Jones <emjones(at)charter.net>

 To: aeroelectric-list(at)matronics.com 

 Sent: Tuesday, May 29,  2012 6:28 AM

 Subject: Re: Found it!

  

 

 --> AeroElectric-List message posted by: "Eric M. Jones" <emjones(at)charter.net (emjones(at)charter.net)>



Dan,



And you don't think this indicates a problem with the Garmin 396?



Swap units and see (or have it checked) before adding filters.



--------

Eric M. Jones

www.PerihelionDesign.com

113 Brentwood Drive

Southbridge, MA 01550

(508) 764-2072

emjones(at)charter.net





Read this topic online here:



http://forums.matronics.com/viewtopic.p;  --> http://www.matronics.com/Navigator?AeroElectric-List======================== [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Tue May 29, 2012 9:32 am Post subject: Found it!

At 08:28 AM 5/29/2012, you wrote:

 	  Quote: 	
		  



Dan,



And you don't think this indicates a problem with the Garmin 396?



Swap units and see (or have it checked) before adding filters.


	


    . . . and make sure that any offending ground

    loop is the manifestation of a wiring architecture

    error.



    There are a lot of those radios flying without

    problems. The elegant solution is to identify root

    cause of the problem . . . but a $11 ground

    loop breaker might be less expensive at this

    stage.

   Bob . . .

dan(at)azshowersolutions.
Guest

Posted: Tue May 29, 2012 10:20 am Post subject: Found it!

[quote]        From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

 To: aeroelectric-list(at)matronics.com 

 Sent: Monday, May 28, 2012 6:20 PM

 Subject: Re: AeroElectric-List: Found  it!

 --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>

At 02:40 PM 5/28/2012, you wrote:

After tracing wires, staring at the Z-16 schematic while going cross-eyed for some time now...I finally found my alternator whine. I thought for sure it was the bridge rectifier I used between the Main and E-buss because when I turned the E-buss on the whine went away. This morning I was doing quite a bit of troubleshooting and happened to try something I somehow overlooked. I turned off my Garmin 396 which has the audio connected to my P-1000  intercom. I think I had done it without the engine running, but today I tried it at idle...and magic happened with no hum at all. I pulled the audio wire from the 396 and started everything up and sure enough, that was it. So now I'm guessing a filter is in order between the 396 and the intercom?  I started searching the net and came up with the PAC RCA Filter SNI-1/3.5

  Filter for what line? Refresh my memory. The pitch

  of the whine changed with engine RPM? Can you run

  the GARMIN from it's own battery supply and still

  have the whine? Does the whine go up and down in

  volume  with any of the system volume controls but

  not others? Bob,  Yes, this was / is certainly an alternator whine. It follows the engine RPM from idle up to about 2200 RPM (remember the Rotax cruise is at or above 5000 RPM) and then became so high pitched it seemed to go away (probably still there but just out of MY ear-drum recieving frequency). I have lived with it for 20 hours of operation and I can send and receive fine on the com radio in flight, however, when I taxi the whine came into play and interfered communications with the Tower and Ground ops.

The Garmin works and sounds fine on its own battery. I have used this unit in other planes and I do have the XM Weather antenna as well as the GPS antenna. When doing this I plug into the audio out and run it to my headset and can hear XM radio as well as terrain alerts loud and clear. 

As indicated I use a at's when I started P-1000 intercom and there is an audio-in wire to that. This is what I have plugged into the 396 audio out. The intercom volume does its job and just increases the whine  db's. the RPM fluctuates the frequency.

I'm betting Bob and Company has something already designed and if so it would be greatly appreciated if I could get the schematic and or instructions. I don't mind building it but if there is an easy go-to at low cost that would be good too.

  I'm still not clear as to why you would have the

  noise when the e-bus is powered through the normal

  feed path but goes away when you close the e-bus

  alternate feed. But knowing that it is associated

  with Garmin ops is helpful.

This was my primary question as well. I had my intercom power coming off of the E-Bus and the Garmin was on the Main. I tried to place both on the same bus thinking that might help, but no joy. When I did that, interestingly the whine did not go away any more as the e-bus switch was closed. That's when I started thinking this was either about the intercom or the 396. That's when I zeroed in on the audio out on the 396. I spent a fair amount of time last night reading your chapter on Electromagnetic Compatability. Correct me here, but I am leaning towards trying to finish off that 1.5V peak to peak unfiltered ripple finding its way from the  alternator. So if this is the case, am I just looking at placing a series Cap (and possibly coupled with an inductor) between the Garmin and the Intercom? I sure this is just a bandaid for  this area and not eliminating the source...but isn't that all we are really doing with this left over ripple?

Thanks

Bob, I ordered your shottkey diode this week in an effort to make this fix. If you have not sent it yet can I cancel order?

  Sure.

  Bob . . .

Un/Subscriptarch & Download, 7-Day Browse, Chat, FAQ,

, and much much more:

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

Dralle, List Admin.

 [b]

dan(at)azshowersolutions.
Guest

Posted: Tue May 29, 2012 10:22 am Post subject: Found it!

Tom, that is an interesting point. I also have one of the Air Gizmo mounts and the wire does tend to get jammed up there.

Dan

 	  Quote: 	
		          From: Tom Chapman <tomrv4(at)me.com>

 To: "aeroelectric-list(at)matronics.com" <aeroelectric-list(at)matronics.com> 

 Sent: Tuesday, May 29, 2012 10:18  AM

 Subject: Re: AeroElectric-List: Re: Found it!

 --> AeroElectric-List message posted by: Tom Chapman <tomrv4(at)me.com (tomrv4(at)me.com)>

I also had a radio noise problem that I finally traced to the audio out line on my 396. It is installed in my panel in an Air Gizmo mount. Turns out the audio out wire was kinking against the back of the mount when I'd stick the unit in. 

I cut away some of the plastic mount right behind the audio out plug, which alleviated the kinking and stopped the radio interference...

Tom

On May 29, 2012, at 8:28 AM, "Eric M. Jones" <emjones(at)charter.net (emjones(at)charter.net)> wrote:

 	  Quote: 	
		   --> AeroElectric-List message posted by: "Eric M. Jones" <emjones(at)charter.net (emjones(at)charter.net)>

 Dan,

 And you don't think this indicates a  problem with the Garmin 396?

 Swap units and see (or have it checked) before adding filters.

 --------

 Eric M. Jones

 www.PerihelionDesign.com

 113 Brentwood Drive

 Southbridge, MA 01550

 (508) 764-2072

 emjones(at)charter.net

 Read this topic online here:

 http://forums.matronics.com/viewtopic.php?p=374160#374160

 http://www.matronics.com/Navigator?AeroElectric-Lnbsp;                    t; 

 [quote][b]

dan(at)azshowersolutions.
Guest

Posted: Tue May 29, 2012 6:17 pm Post subject: Found it!

[quote]Found this thread on VansAirforce  http://www.vansairforce.com/community/showthread.php?t=17882

It looks like this is a common problem with the Garmin 396. 

  Dan

  

 

 --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>



At 08:28 AM 5/29/2012, you wrote:

 	  Quote: 	
		   --> AeroElectric-List message posted by: "Eric M. Jones" <emjones(at)charter.net (emjones(at)charter.net)>

 

 Dan,

 

 And you don't think this indicates a problem with the Garmin 396?

 

 Swap units and see (or have it checked) before adding filters.


	


   . . . and make sure that any offending ground

   loop is the manifestation of a wiring architecture

   error.



   There are a lot of those radios flying without

   problems. The elegant solution is to identify root

   cause of the problem . . . but a $11 ground

   loop breaker might be less a href="http://www.matronics.com/Navigator?AeroElectric-List" target="_   nbsp;                    ================



 

 

 [b]

nuckolls.bob(at)aeroelect
Guest

Posted: Tue May 29, 2012 6:32 pm Post subject: Found it!

At 09:14 PM 5/29/2012, you wrote:

  	  Quote: 	
		    Found this thread on VansAirforce   http://www.vansairforce.com/community/showthread.php?t=17882

  It looks like this is a common problem with the Garmin 396. 

  Dan

  	


   Okay, where does the 396 get power ground. Try grounding it

   to the same place all the audio-lo or shield grounds get

   connected.



 

 

   Bob . . .    [quote][b]

dan(at)azshowersolutions.
Guest

Posted: Tue May 29, 2012 6:53 pm Post subject: Found it!

[quote]        From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

 To: aeroelectric-list(at)matronics.com 

 Sent: Tuesday, May 29, 2012 7:31 PM

 Subject: Re: Re: Found it!

   At 09:14 PM 5/29/2012, you wrote:

  	  Quote: 	
		    Found this thread on VansAirforce  http://www.vansairforce.com/community/showthread.php?t=17882

  It looks like this is a common problem with the Garmin 396. 

  Dan

   Okay, where does the 396 get power ground. Try grounding it

   to the same place all the audio-lo or shield grounds get

   connected.

     Bob . . .    

 	  Quote: 	
		  Will take another look Bob. Thanks http://www.matronics.com/Navigator?AeroElectric-List===================

 [b]

nuckolls.bob(at)aeroelect
Guest

Posted: Wed May 30, 2012 7:00 am Post subject: Found it!

At 09:52 PM 5/29/2012, you wrote:



 

  	  Quote: 	
		   

  From:[/b] "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

  To:[/b] aeroelectric-list(at)matronics.com 

  Sent:[/b] Tuesday, May 29, 2012 7:31 PM

  Subject:[/b] Re: Re: Found it!

 

  At 09:14 PM 5/29/2012, you wrote: 	  Quote: 	
		    Found this thread on VansAirforce   http://www.vansairforce.com/community/showthread.php?t=17882 It looks like this is a common problem with the Garmin 396.  Dan 	
 

    Okay, where does the 396 get power ground. Try grounding it

    to the same place all the audio-lo or shield grounds get

    connected.



 

    Bob . . . 



   	  Quote: 	
		  Will take another look Bob.

Thanks [/b] 	
	
 

  

   Just dug up the manual on the 396. I'm 99% certain

   that this is a ground loop problem. The telling

   symptom is alternator noise that increases with

   ship's loads when substantial currents travel over

   the airframe. I'll bet if you move the Garmin

   DC(-) lead to the same ground as all the avionics/

   audio system grounds, the noise will go away.



   Bob . . .    [quote][b]

dan(at)azshowersolutions.
Guest

Posted: Wed May 30, 2012 7:42 am Post subject: Found it!

From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

 To: aeroelectric-list(at)matronics.com 

 Sent: Wednesday, May 30, 2012 7:56 AM

 Subject: Re: Re: Found it!

  

 

   At 09:52 PM 5/29/2012, you wrote:



 

  	  Quote: 	
		   

  From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

  To: aeroelectric-list(at)matronics.com 

  Sent: Tuesday, May 29, 2012 7:31 PM

  Subject: Re: Re: Found it!

 

  At 09:14 PM 5/29/2012, you wrote: 	  Quote: 	
		    Found this thread on VansAirforce  http://www.vansairforce.com/community/showthread.php?t=17882 It looks like this is a common problem with the Garmin 396.  Dan 	
 

    Okay, where does the 396 get power ground. Try grounding it

    to the same place all the audio-lo or shield grounds get

    connected.



 

    Bob . . . 



   	  Quote: 	
		  Will take another look Bob.

Thanks 	
	
    

   Just dug up the manual on the 396. I'm 99% certain

   that this is a ground loop problem. The telling

   symptom is alternator noise that increases with

   ship's loads when substantial currents travel over

   the airframe. I'll bet if you move the Garmin

   DC(-) lead to the same ground as all the avionics/

   audio system grounds, the noise will go away.



   Bob . . .    

[quote]OK, I won't be able to get to the airport for a couple days, but I will play with the ground wires then and report back.Danhttp://www.matronics.co====


[b]

dan(at)azshowersolutions.
Guest

Posted: Wed May 30, 2012 6:44 pm Post subject: Found it!

From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

 To: aeroelectric-list(at)matronics.com 

 Sent: Tuesday, May 29, 2012 7:31 PM

 Subject: Re: Re: Found it!

   At 09:14 PM 5/29/2012, you wrote:

  	  Quote: 	
		    Found this thread on VansAirforce  http://www.vansairforce.com/community/showthread.php?t=17882

  It looks like this is a common problem with the Garmin 396. 

  Dan

   Okay, where does the 396 get power ground. Try grounding it

   to the same place all the audio-lo or shield grounds get

   connected.

     Bob . . .    

[quote]I did get to the hanger today and quickly pulled the wires out into the open that has the 3.5mm plug (one that goes into the Garmin). Can you explain the lo / hi audio wire thing. Am I to understand that the lo is to be soldered to the ground? This may be my goof as I purchased this plug (which

 is stereo and my intercom is not). I think I may have soldered the two wires to right and left and the ground might be left out in the cold. Will need to double check, but I looked up the PM 1000 pin-out after I got home so it may be in the soldering of that plug. I purchased the solderable mini plug in stereo config as I wanted to hear the music / alerts in both sides of headset. Thoughts? Common mistake?http://www.matronics.com/Navigator?AeroElectric-List[b]

nuckolls.bob(at)aeroelect
Guest

Posted: Wed May 30, 2012 7:26 pm Post subject: Found it!

Bob . . . 



 I did get to the hanger today and quickly pulled the wires out into the open that has the 3.5mm plug 



 (one that goes into the Garmin). Can you explain the lo / hi audio wire thing. 



   In a monophonic audio cable with 3.5 mm plug, the tip is

   connected to the signal/center/hi lead, the sleeve is

   connected to the shield/ground/lo lead.



   A stereo cable adds another free conductor and the

   two signal wires become right and left audio. The

   shield/ground/lo lead still connects to the sleeve.



   The larger analogy can be seen on a legacy microphone

   connector



  http://aeroelectric.com/articles/micjack/micjack.html



 Am I to understand that 



 the lo is to be soldered to the ground? This may be my goof as I purchased this plug (which

 is stereo and my intercom is not). I think I may have soldered the two wires to right and left and the ground 

 might be left out in the cold. Will need to double check, but I looked up the PM 1000 pin-out after I 

 got home so it may be in the soldering of that plug. I purchased the solderable mini plug in stereo 

 config as I wanted to hear the music / alerts in both sides of headset.



     I'm confused. If you have stereo headsets, then you would

     need to install 3-circuit jacks and tie both r/l audio

     from headset together to be treated as a mono headset.

     This is the only place you would use a 3-ckt jack.



     The PM1000 MUSIC IN is monophonic which would required

     blending r/l channels together BEFORE wiring the blend

     into pin 20 and the lo/gnd side to pin 7.



 [img]cid:.0[/img]

    



 

    This would call for a 2-ckt plug to do the mate up between

    the Garmin and the PS1000. And just for grins, I'd use

    pin 7 of the PS1000 for BOTH audio ground and DC power

    ground for the Garmin.



     http://tinyurl.com/7ypuofg

 [img]cid:.1[/img]

 [quote]   Unless you have stereo audio to handle, a simple 2-ckt plug/jack    combination will suffice. The mis-application of the 3-ckt jack    may indeed be contributing to your problem.  

   Bob . . .[/b]

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dan(at)azshowersolutions.
Guest

Posted: Thu May 31, 2012 6:19 am Post subject: Found it!

Thanks Bob, That brought it home for me. Off to get a 2-ckt plug.

Dan





        From: "Robert L.  Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

 To: aeroelectric-list(at)matronics.com 

 Sent: Wednesday, May 30, 2012 8:24 PM

 Subject: Re: Re: Found it!

  

 

   

   Bob . . . 



 I did get to the hanger today and quickly pulled the wires out into the open that has the 3.5mm plug 



 (one that goes into the Garmin). Can you explain the lo / hi audio wire thing. 



   In a monophonic audio cable with 3.5 mm plug, the tip is

   connected to the signal/center/hi lead, the sleeve is

   connected to the shield/ground/lo lead.



   A stereo cable adds another free conductor and the

   two signal wires become right and left audio. The

   shield/ground/lo lead still connects to the sleeve.



   The larger analogy can be seen on a legacy microphone

   connector



  http://aeroelectric.com/articles/micjack/micjack.html



 Am I to understand that 



 the lo is to be soldered to the ground? This may be my goof as I purchased this plug (which

 is stereo and my intercom is not). I think I may have soldered the two wires to right and left and the ground 

 might be left out in the cold. Will need to double check, but I looked up the PM 1000 pin-out after I 

 got home so it may be in the soldering of that plug. I purchased the solderable mini plug in stereo 

 config as I wanted to hear the music / alerts in both sides of headset.



     I'm confused. If you have stereo headsets, then you would

     need to install 3-circuit jacks and tie both r/l audio

     from headset together to be treated as a mono headset.

     This is the only place you would use a 3-ckt jack.



     The PM1000 MUSIC IN is monophonic which would required

     blending r/l channels together BEFORE wiring the blend

     into pin 20 and the lo/gnd side to pin 7.



 [img]cid:1.3820927360(at)web2811.biz.mail.ne1.yahoo.com[/img]

    



 

    This would call for a 2-ckt plug to do the mate up between

    the Garmin and the PS1000. And just for grins, I'd use

    pin 7 of the PS1000 for BOTH audio ground and DC power

    ground for the Garmin.



     http://tinyurl.com/7ypuofg

 [img]cid:2.3820927360(at)web2811.biz.mail.ne1.yahoo.com[/img]

  	  Quote: 	
		     Unless you have stereo audio to handle, a simple 2-ckt

plug/jack

   combination will suffice. The mis-application of the 3-ckt

jack

   may indeed be contributing to your problem.


 

  Bob . . .

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dan(at)azshowersolutions.
Guest

Posted: Sun Jun 10, 2012 7:21 am Post subject: Found it!

I just wanted to stop and thank everyone for their suggestions and help as I was searching for this gremlin. The fix did turn out to be installing that $11 in-line audio filter into the audio jack on the 396 and sending it on its way to the intercom. Jumped in, fired it up and taxied around for the first time in peace and quiet. 

Dan

        From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

 To:  aeroelectric-list(at)matronics.com 

 Sent: Wednesday, May 30, 2012 7:56 AM

 Subject: Re: Re: Found it!

   At 09:52 PM 5/29/2012, you wrote:

  	  Quote: 	

  From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

  To: aeroelectric-list(at)matronics.com 

  Sent: Tuesday, May 29, 2012 7:31 PM

  Subject: Re: Re: Found it!

  At 09:14 PM 5/29/2012, you wrote: 	  Quote: 	
		    Found this thread on VansAirforce  http://www.vansairforce.com/community/showthread.php?t=17882 It looks like this is a common problem with the Garmin 396.  Dan 	

    Okay, where does the 396 get power ground. Try grounding it

    to the same place all the audio-lo or shield grounds get

    connected.

    Bob . . . 

   	  Quote: 	
		  Will take another look Bob.

Thanks 	

   Just dug up the manual on the 396. I'm 99% certain

   that this is a ground loop problem. The telling

   symptom is alternator noise that increases with

   ship's loads when substantial currents travel over

   the airframe. I'll bet if you move the Garmin

   DC(-) lead to the same ground as all the avionics/

   audio system grounds, the noise will go away.

   Bob . . .    

[quote]http://www.matronics.co====

[b]

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jun 16, 2012 1:36 pm Post subject: Found it!

At 10:19 AM 6/10/2012, you wrote:

I just wanted to stop and thank everyone for their suggestions and 

help as I was searching for this gremlin. The fix did turn out to be 

installing that $11 in-line audio filter into the audio jack on the 

396 and sending it on its way to the intercom. Jumped in, fired it up 

and taxied around for the first time in peace and quiet.



    The 'filter' is probably a simple isolation

    transformer as opposed to any sort of noise

    rejection device. This technique is used to

    break any potential (orrealized) ground loop.



    Back in the good ol' days, audio inputs and many

    outputs from the 'higher end' devices had such

    transformers built in. These were common to audio

    amplifiers for large installations that might have

    signal or microphone cables hundreds of feet long.

    I used to shag audio systems for a group of acoustic

    music aficionados and learned about the usefulness

    of such devices first hand. When your mixer board was

    100+ feet of wire away from the power amplifiers, the

    potential for ground loop noises was very high.



    Yeah, even carried the stuff around in a VW microbus,

    just no psychodelic paint job!



    There have been cases where I would have liked to

    install such a transformer in TC aircraft . . . but

    that's a "no-no" without a lot of paperwork; change

    of configuration. Hence, it's not uncommon to hear

    buzzes, whines, pops, etc. in the audio systems for

    REALLY expensive machines.



    It would have been interesting to locate root

    cause for the original loop, but not worth tearing

    into hard-to-get-at wire bundles, etc. None-the-less,

    a loop-breaker transformer is an elegant fix.

   Bob . . .

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