I have an issue with what I believe to be isolated to the back seat intercom in my 01 Husky A1B. I have owned the plane for a couple of years and have always had terrible background noise being picked up by the head phone mics. Went to Noise cancelling head sets and that helped so I lived with it. The radio was a Garmin 430. I recently trade up to a new Avidyne IFD 440 but still have the excessive background noise. I have the same audio control panel (Garmin GMA 340). Im new to both flying and aircraft ownership having bought my Husky to learn to fly in and have about 175 hrs total since earning my license in Sept 2015.I have played around with various adjustments on the GMA 340 and hit the holy grail the other day while flying with a passenger in back seat after hitting the pilot isolate (shutting out the back seat from radio/intercom). With the pilot isolate on it was amazing. Absolutely silent except for crisp, clear radio calls from Nor Cal and other aircraft. ZERO background noise. This is how I know its the backseat position picking up the ambient noise. Its not a engine power specific issue per say and I don't believe its a interference or shielding issue (no clicking or pulse to the noise, just loud ambient cockpit noise like its the backseat mic picking up a hot mic).

Any suggestions? Changing out headsets didn't change anything...

Thanks
Greg

Two choices, either get the audio panel fixed (it shouldn't make the backseat mic hot unless someone's talking on it), or replace the audio panel. Personally, I really like the audio panels by PS Engineering. That's all that they make, either audio panels with built in intercoms or straight intercoms. They're the best in the business. When I replaced mine with a PS Engineering 6000B (their lowest cost audio panel), I was amazed at the difference from what I had.

Cary

Thank you Cary! Thats what I thought was the fix. I just needed to hear from someone with more experience/knowledge than me. Some circuit failing in the open position for that channel (backseat) mic makes total sense. I think Im going to look at the new avidyne audio panel (AMX240) to give me a couple of added features for the new IFD 440 I have (2nd channel monitoring). $2100 is painful though after just installing the Aspen Pro 1000 PFD and IFD 440.

Thanks again.
Greg

Whoa! Buying a new comm panel is an expensive troubleshooting step (no offense, Cary). I had a very similar and highly annoying issue in my 180. The pilot's side mike would intermittently stick in transmit, and I had no side tone almost all the time. Thinking my comm panel was to blame, I had it rebuilt by Garmin for $250. They found nothing wrong, but replaced the electronic internals just the same. I reinstalled it with high hopes that my problem was fixed. It wasn't. Then I got a friend who is an avionics tech involved and within 15 minutes under my panel he had traced the problem to the pilot's side mike Jack grounding out against the panel.

I'd start by loosening the nut on your rear seat mike jack and wiggling it a bit with your headset plugged in and see if that causes the problem come or go. You might also disassemble the mike jack and see if you have a frayed wire or some such. If you're still suspecting the comm panel after that, I'd recommend a rebuild before a replacement.

Good luck!


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Check the rear jacks and make sure the plugs have a collared washer/insulator on them.
DENNY

And find a good avionics shop somewhere close and make an appointment. Should be an easy fix.

MTV

Also, ring out the mic jack to ground to ensure that you don't have a wire rubbed through and grounding out. Ring it out to ground and also the phone jack. These are added tests to the few above. Much cheaper starting points then buying a new audio panel.

Thanks for the posts. I'll do the rear jack test as suggested. Much appreciated

Greg

No offense taken, Felix, and good advice from everyone who leaped in, too--I jumped ahead too quickly, and the other suggestions of first checking the mic jack for the back seat makes sense. I should have known that, as I had a similar (not the same) simple-to-fix problem with my old intercom that was fixed by just tightening the knurled nut that holds the mic jack in place--my problem was an intermittent failure to transmit when I'd key the yoke button on the pilot's side. It's a variation of the KISS principle--look for the simplest solution first. Mea culpa.

If it turns out that the simple "fix" doesn't fix it, then I'd consider having the existing audio panel fixed, too--I think I said that--less expensive than replacing it. But if there are other issues with that box and you decide to replace it, then I'd still recommend a PS Engineering box before any other brand. I think they're head and shoulders above all of the other avionics manufacturers when it comes to audio panels and intercoms, including Garmin, Bendix-King, and Avidyne.

I'm a real believer in getting the best box for the purpose. Virtually all of today's avionics brands are able to work with each other. I know some owners want every faceplate to say the same brand, but that's really not necessary. In my panel, I have the PS Engineering audio panel, a Garmin 430W as #1 nav/com/GPS, a Bendix King KT74 transponder, a Narco Mark 12D as #2 nav/com, and a (pre Bendix) King KR-87 ADF. All of them work well together.

Cary

Apologies if this has already been done, however...

Even before you wring out wires and jacks, make sure the squelch on the passenger intercom is adjusted correctly. I used to fly dozens of customer airplanes with GMA 340s in them, and every so often one of the squelch knobs was all the way to the stop. I don't know how they couldn't have known it wasn't correct, but it was surprisingly common, especially among new owners.

A1Skinner wrote:Also, ring out the mic jack to ground to ensure that you don't have a wire rubbed through and grounding out. Ring it out to ground and also the phone jack. These are added tests to the few above. Much cheaper starting points then buying a new audio panel.

Im not sure what you mean exactly (ring it out). Sorry! I gained access to the panel yesterday and using my digital MM I was able to check continuity on the jacks and found no issue with ground. Visually, everything looked tight and all the associated wiring looked solid with no exposed wiring and good connections. My wife flew back seat yesterday and definitely confirmed its a hot mic issue. Problem solved when she unplugged just the MIC jack. Squelch seemed to be adjusted appropriately. Trouble shooting is narrowing it down to some issue internally with the 16 year old factory installed GMA 340 audio panel. Off to the avionics shop now I guess.

Thanks to all who have responded.

Greg

gregwyatt wrote:

A1Skinner wrote:Also, ring out the mic jack to ground to ensure that you don't have a wire rubbed through and grounding out. Ring it out to ground and also the phone jack. These are added tests to the few above. Much cheaper starting points then buying a new audio panel.

Im not sure what you mean exactly (ring it out). Sorry! I gained access to the panel yesterday and using my digital MM I was able to check continuity on the jacks and found no issue with ground. Visually, everything looked tight and all the associated wiring looked solid with no exposed wiring and good connections. My wife flew back seat yesterday and definitely confirmed its a hot mic issue. Problem solved when she unplugged just the MIC jack. Squelch seemed to be adjusted appropriately. Trouble shooting is narrowing it down to some issue internally with the 16 year old factory installed GMA 340 audio panel. Off to the avionics shop now I guess.

Thanks to all who have responded.

Greg

Greg,

If you had a hot mic, how did you verify that "Squelch seemed to be adjusted appropriately"? Just curious.

MTV

mtv wrote:

gregwyatt wrote:

A1Skinner wrote:Also, ring out the mic jack to ground to ensure that you don't have a wire rubbed through and grounding out. Ring it out to ground and also the phone jack. These are added tests to the few above. Much cheaper starting points then buying a new audio panel.

Im not sure what you mean exactly (ring it out). Sorry! I gained access to the panel yesterday and using my digital MM I was able to check continuity on the jacks and found no issue with ground. Visually, everything looked tight and all the associated wiring looked solid with no exposed wiring and good connections. My wife flew back seat yesterday and definitely confirmed its a hot mic issue. Problem solved when she unplugged just the MIC jack. Squelch seemed to be adjusted appropriately. Trouble shooting is narrowing it down to some issue internally with the 16 year old factory installed GMA 340 audio panel. Off to the avionics shop now I guess.

Thanks to all who have responded.

Greg

Greg,

If you had a hot mic, how did you verify that "Squelch seemed to be adjusted appropriately"? Just curious.

MTV

By ringing out I meant checking it with an Ohm meter. Sorry for not being clear Greg, seems like you got it figured though.
Mike, I'm pretty sure squelch would cause the hot mike all the time, plugged in or unplugged. I thinks he's on the right track with sending the GMA out.

I simply adjusted the squelch at various points (co-pilot) looking for the point where normally squelch would break to open mic but since open mic is constant at back seat it doesn't change.

Thanks MTV

Greg

The intercom squelch should be able to kill the open mike unless its open due to being in transmit mode.. I have flown with some pretty high time students who didn't realize there are both radio squelch and intercom squelch. Have you tried switching headsets front to back? The mike gain on the rear headset may be set too high.
Tom