Electronic/engine noise coming through headset

birdus

birdus

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Jay Williams
What's the cause of electronic noise coming out of the intercom and how can I get rid of it? I have a Luscombe 8E with electrical system and a new PS Engineering 1000II intercom. I can definitely hear the pitch of the noise increase and decrease with engine RPM. Thoughts?
 
Alternator whine. In older airplanes it's often caused by an electrical ground loop, where stray alternator charge currents travel through the airframe and find their way into the audio stuff. Ask your avionics guys if they installed the headset jacks with insulators to isolate the audio ground from airframe ground at the jacks. The jacks should only be grounded by dedicated wires that go back to the intercom, or by the cable shielding to the same place. If there's a jack for the handheld mike, don't forget it, too.
 
Dan Thomas said:
Alternator whine. In older airplanes it's often caused by an electrical ground loop, where stray alternator charge currents travel through the airframe and find their way into the audio stuff. Ask your avionics guys if they installed the headset jacks with insulators to isolate the audio ground from airframe ground at the jacks. The jacks should only be grounded by dedicated wires that go back to the intercom, or by the cable shielding to the same place. If there's a jack for the handheld mike, don't forget it, too.
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Interestingly enough, one of the other things we did to the plane (among myriad) was to replace the generator with an alternator, so it seems merely finding out if "it did this before the new intercom" may not solve the issue. I'm going to listen to one of my first videos in the plane to find out how it sounded before all the work.
 
Kill the Alt field and verify it goes away. It could be a noisy alternator. It could also be a Alt power wire routed near antenna cables or audio wires.
 
Listened to my first video recording (first flight). There was just a portable intercom in the plane then. There was lots of hiss, but that's it. I then listened to the most recent video (new intercom and lots of other new stuff, including alternator). There's hiss, but also a tone/pitch which varies in proportion to RPM. Moreover, there is some moderately consistent beeping. In both cases, the offensive sounds are at least reduced while talking/transmitting.
 
birdus said:
. In both cases, the offensive sounds are at least reduced while talking/transmitting.
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Many intercoms have a music input which is reduced in volume whenever the mic is active. Do you have anything connected to the music input?
 
What headset are you using? Have you tried a different one?
 
birdus said:
Listened to my first video recording (first flight). There was just a portable intercom in the plane then. There was lots of hiss, but that's it. I then listened to the most recent video (new intercom and lots of other new stuff, including alternator). There's hiss, but also a tone/pitch which varies in proportion to RPM. Moreover, there is some moderately consistent beeping. In both cases, the offensive sounds are at least reduced while talking/transmitting.
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That beeping is probably the strobe. Again, it's a ground-loop issue, most likely, same as the alternator whine, and those headset jacks, I bet, weren't insulated from the panel. Ask the avionics guys. If they know their stuff they'll have answers.

There's aslo the possibility that the alternator wasn't installed with a filter capacitor on the field input, nor a noise suppressor on the output. That lets noise get into the bus, where it can cause headset noise, but it won't explain the strobe noise. That's a ground-loop issue, and ground currents in the airframe get into that jack, pass through the headset mike and phone circuits, get to the intercom where they are amplified and sent back to the phones. Insulating the jacks is a first step that should have been done anyway.
 
Nothing music-related involved. I have a brand new Bose A20.

I helped the A&P with all the work. I installed some of the headphone jacks (he did the two that go directly into the radio). If I recall correctly, I believe there were black plastic sleeves that went between the jacks and the panel.

Thanks for the suggestions, everyone. I'll talk to my A&P. Just wanted to get some ideas here first.
 
We Get some high pitched ringing when the Pitot Heat is on so I feel your pain some.
 
Jonny Sprague said:
We Get some high pitched ringing when the Pitot Heat is on so I feel your pain some.
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A significant load works the alternator harder and more alternator whine is generated.
 
birdus said:
Nothing music-related involved. I have a brand new Bose A20.

I helped the A&P with all the work. I installed some of the headphone jacks (he did the two that go directly into the radio). If I recall correctly, I believe there were black plastic sleeves that went between the jacks and the panel.

Thanks for the suggestions, everyone. I'll talk to my A&P. Just wanted to get some ideas here first.
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There are two pieces to those insulators. The stepped sleeve/washer and a flat plastic washer that goes under the nut and metal washer.
 
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