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Whine in headset

thompsonbr87

thompsonbr87

Well Known Member
After installing a new radio, audio panel, and stereo headset jacks, I have introduced some sort of electrical whine into my audio system. The tone seems to be RPM dependent - high RPM = higher pitch. The whining sound seemed to be intermittent, but there wasn't anything apparent that made it cut in and out. Could be heard through both Lightspeed and Bose headsets in pilot & co-pilot jacks.

Reading some old posts, it sounds like it is likely related to the alternator? Some have fixed their problems by replacing diodes or noise filters (that's getting above my current knowledge level at the moment)? I did all of my own wiring on the upgrade, and I think it is more likely that my inexperience has somehow caused this than rather something failing on the alternator coincidentally.

What else could I be potentially looking for? While researching and learning, I kept reading about ground loops. What does that actually sound like? I am currently under the impression that a ground loop is more of a static sound than a whining sound.
 
A ground loop is a likely source of the noise, which is likely from the alternator. What happens is a small amount of the alternator current seeking to get back to the negative battery terminal is running thru the ground wire of an audio cable, inducing a small ac voltage drop that you hear. What you should have is:
1. Separate ground wires for the headphones and mike (not the shield).
2. Standard jacks must be isolated from any airframe metal.
3. Shield should not be connected at the jack (if you did #1).

Look carefully at all jacks for #2. One of the fiber washers must have a shoulder on it to go inside the hole. Sometimes the metal part of the jack is in accidental contact with the airframe. Truth is these problems can be tough to find.
 
I located my ground loop a while back, but though it would be good to post a quick follow-up on this that might help someone in the future.

I had checked and double checked all of my headset jacks, even making sure the area on the backside of the jacks were clear. I checked that all shielding was appropriately grounded. I turned my radios on together, individually, and then both off. Adjusted volumes on radios, headsets, & intercom. Tried different headsets (both ANR & PNR). I noticed that using the pilot isolate intercom feature would silence the whine. I could also turn the audio panel off completely to fix the problem (PMA-8000B has a fail-safe mode which keeps COM 1 active in the pilot's headset). I finally finally found a pattern to the intermittent nature of the whine when I realized that it stopped momentarily by breaking the squelch on the intercom or transmitting/receiving, however, after a few seconds the whine returned. This was exactly how the music muting feature on the audio panel should be working. I disconnected the music jack from the instrument panel, and sure enough, problem solved! I learned something new that day. Through a thread on another (forum that I can no longer locate), I discovered that the music jack has a small shoulder at the base of the sleeve that should isolate the sleeve from the mounting hole. I had only drilled out the hole to the size of the sleeve itself. I did have a little trouble finding a washer to isolate the nut - the thickness of panel left almost no extra depth, but I did find a nylon washer that is thin enough for me to get the nut on the threads. If it doesn't hold, I may try to find a jack with longer threads, but it seems to be ok for now.

Looking back on it, I feel like I should've located the problem more quickly. Of course, knowing what I know now, it's blatantly obvious. The adage about hindsight rings true...
 
thompsonbr87 said:
I located my ground loop a while back, but though it would be good to post a quick follow-up on this that might help someone in the future.

I had checked and double checked all of my headset jacks, even making sure the area on the backside of the jacks were clear. I checked that all shielding was appropriately grounded. I turned my radios on together, individually, and then both off. Adjusted volumes on radios, headsets, & intercom. Tried different headsets (both ANR & PNR). I noticed that using the pilot isolate intercom feature would silence the whine. I could also turn the audio panel off completely to fix the problem (PMA-8000B has a fail-safe mode which keeps COM 1 active in the pilot's headset). I finally finally found a pattern to the intermittent nature of the whine when I realized that it stopped momentarily by breaking the squelch on the intercom or transmitting/receiving, however, after a few seconds the whine returned. This was exactly how the music muting feature on the audio panel should be working. I disconnected the music jack from the instrument panel, and sure enough, problem solved! I learned something new that day. Through a thread on another (forum that I can no longer locate), I discovered that the music jack has a small shoulder at the base of the sleeve that should isolate the sleeve from the mounting hole. I had only drilled out the hole to the size of the sleeve itself. I did have a little trouble finding a washer to isolate the nut - the thickness of panel left almost no extra depth, but I did find a nylon washer that is thin enough for me to get the nut on the threads. If it doesn't hold, I may try to find a jack with longer threads, but it seems to be ok for now.

Looking back on it, I feel like I should've located the problem more quickly. Of course, knowing what I know now, it's blatantly obvious. The adage about hindsight rings true...
Click to expand...

I suspect this is a common issue. I really struggled to find a jack with enough depth to accommodate both needed washers.
 
lr172 said:
I suspect this is a common issue. I really struggled to find a jack with enough depth to accommodate both needed washers.
Click to expand...

A couple of other thoughts I had were increasing the panel cut-out size and making a mounting plate just large enough to accommodate the full body of the jack. Or slightly counterboring to the size of the washer - maybe driving a step drill bit by hand? Also considered putting in a 1/4" jack and using a 1/4" to 1/8" cable to connect music.
 
I had a similar problem. I drilled the hole in the panel big enough so the jack didn't touch the edges and mounted a piece of plastic behind it. I then mounted the jack to the plastic. (this was the audio input jack)
 
Last edited:
thompsonbr87 said:
A couple of other thoughts I had were increasing the panel cut-out size and making a mounting plate just large enough to accommodate the full body of the jack. Or slightly counterboring to the size of the washer - maybe driving a step drill bit by hand? Also considered putting in a 1/4" jack and using a 1/4" to 1/8" cable to connect music.
Click to expand...

Thanks. I did ultimately find a jack with enough depth and a thin enough shoulder washer. I was mentioning for others sake, as it was not easy to find and the common ones are just begging for someone to leave out one of the washers in our application.

Larry
 
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