cackling in my headset

[RobertE]

I'm getting a cackling (sounds like bacon frying) in my headset.  It diminishes greatly if I impose an electrical load such as nav lights.  But if there is no load other than the radios and transponder the cackles are, truly, like several strips of bacon.

I've got voltage displayed on my 696 and it shows 14.1 and, occasionally, 14.2.  My norm after cruising for awhile is 14.1.Maybe it has always touched 14.2 from time to time but I've not noticed it before.  The ammeter shows its normal indication, which is a very slight charge (about a half needle width).  I've got a J model with a 12 volt system, as you would have guessed.

Anyone know what this is?

Thanks.

[takair]

Could be a few things, but very likely a ground somewhere.  First, did it start suddenly?  Did you add anything, like a USB port or adaptor?  Have you tried pulling the alternator breaker?  Does the noise change if you move the headset jacks?  Can you turn off your intercom?  Radios, etc?  These are just septa rating points for tshooting...

[RobertE]

All good questions.  I'll do more thorough testing but as to a couple questions, a) it came on slowly (noticed it about a month ago but I might get one "cackle" every 5 seconds back then vs continuous if little load is imposed, and  the only change recently was a rebuilt alternator. 

[LANCECASPER]

cackling. 1 : to make the noise or cry a hen makes especially after laying an egg. 2 : to laugh or chatter noisily.

crackling 1.the making of slight cracking sounds rapidly repeated. 2.the crisp browned skin or rind of roast pork.  3.Usually, cracklings. Southern U.S. the crisp residue left when fat,especially hog or chicken fat, is rendered.

It sounds like you have either (1) a chicken laying an egg in the backseat with a headset and mic on or (2) maybe someone frying bacon in the backseat. If you're smelling bacon also I'd say it's #2. Is this happening just in the mornings around breakfast time?

Seriously though I would try to isolate it by turning everything off and then adding radio by radio. Make sure it is not the headset you are using. 

Edit - just noticed your 2nd post re: the alternator. That sounds like the culprit especially if it improved when you add more load.

[eman1200]

Did someone say bacon?!?

[RobertE]

Well, I did some troubleshooting today.  If this helps anyone figure it out, just speak up.

1. It goes away if I pull the field circuit to the generator

2. I have the noise in both pilot and copilot positions and regardless of the headset used

3. I goes away if i impose even just a modest load in excess of radios and transponder (adding the autopilot or nav lights quiets it)

4. It doesn't seem to bear any relation to indicated voltage which typically varies between 13.9 and 14.1 volts

Thanks.

[takair]

Robert

want to confirm that you have an alternator and not a generator.  Cracking can be brushes not quite broken in or toward the end of life.  Could also be a bad ground or bad connection on the alternator or engine.  Probably want to start there.  In both cases you may have high resistance that is partially overcome with increased current flow.   However, it may be an indication of bigger problems if not found now.  I'd pull the cowl as a start..

[RobertE]

I've got an alternator.  I'll clean all the connections and see if that does the trick.

 

 

[takair]

Check the big bond strap from engine to airframe too.

[Piloto]

Robert

You don't mention if the noise is also heard on the plane speaker. If not heard on the plane speaker the source is most likely at the audio panel or headphone jack. If this is the case pull out the audio panel and spray contact cleaner at the tray and unit connectors. Also spray at the headphone jack connectors.

José

[RobertE]

I figure I should close the loop on this for the benefit of anyone who might have a similar problem.

The alternator was returned to the shop that overhauled it, they suspected a faulty diode but found none.  However upon returning everything to service the cackling has stopped.  Not one pop.  Upon reinstallation my mechanic added a shielded ground wire to the field circuit.  So either the act of removing and then reinstalling the alternator tightened up a previously loose connection or the shielded ground wire did the trick.  

 

FYI

[Marauder]

I figure I should close the loop on this for the benefit of anyone who might have a similar problem.

The alternator was returned to the shop that overhauled it, they suspected a faulty diode but found none.  However upon returning everything to service the cackling has stopped.  Not one pop.  Upon reinstallation my mechanic added a shielded ground wire to the field circuit.  So either the act of removing and then reinstalling the alternator tightened up a previously loose connection or the shielded ground wire did the trick.  

 

FYI

Gotta love gremlins.

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