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Electrical / Audio question?

Shark

Shark

Well Known Member
When I hook up my audio cable, I get a strange feedback that has a certain frequency which changes with my engine RPMs. Also my lights dim and brighten at the same frequency and also changes with the RPMs. I put a new alternator and a new voltage regulator and made sure the alternator was grounded but I’m still lost. Here is a video of the terrible feedback https://youtu.be/CLPam-rajs0 Hoping for some answers. Thank you.
 
Last edited:
The high-pitched whine is classic ground loop noise from the alternator, which goes up in pitch as the engine (and alternator) RPM increases. Usual cause is multiple ground paths, one or more of which have less than perfect (zero) resistance. These are a bear to track down in a finished airplane.
The (about) 3 times a second "beeps" are some load which is turning on and off 3 times a second. It might be the regulator, too, if it is of the old on-off relay design. When I owned a 182 it used to do exactly this, except it was once a second, as the 10 amp tail beacon cycled on/off.
 
You need to check that audio GND is not connected to aircraft GND.
The audio plugs have to be isolated from the instrument panel. No contact.
There are plastic washers to be used with audio plugs for isolation from GND.

Good luck
 
+1

Avanza said:
You need to check that audio GND is not connected to aircraft GND.
The audio plugs have to be isolated from the instrument panel. No contact.
There are plastic washers to be used with audio plugs for isolation from GND.

Good luck
Click to expand...

Good advice, I had similar issues with audio and it was because I had the shield/ground tied at both ends, disconnected from the plug (just connected at the intercom end) and problem went away, good luck.
Figs
 
Tell us more about this

Also my lights dim and brighten at the same frequency and also changes with the RPMs.
 
Friday

BobTurner said:
The high-pitched whine is classic ground loop noise from the alternator, which goes up in pitch as the engine (and alternator) RPM increases. Usual cause is multiple ground paths, one or more of which have less than perfect (zero) resistance. These are a bear to track down in a finished airplane.
The (about) 3 times a second "beeps" are some load which is turning on and off 3 times a second. It might be the regulator, too, if it is of the old on-off relay design. When I owned a 182 it used to do exactly this, except it was once a second, as the 10 amp tail beacon cycled on/off.
Click to expand...

after reading this I am going to spend some time this weekend checking / replacing the grounds
 
Still No Luck

Spent the weekend in the hangar, it was wonderful, but no luck. Cleaned up grounds also replaced / re routed battery ground, engine ground. When that didn't work I robbed the alternator off my RV3 to see if it was the alternator causing the light dimming, no such luck, same thing. Tonight I am climbing under the panel to check the radio rounds and the plug wiring. I am definitely running out of ideas. The only thing I can think of is the regulator?
 
Sure sounds like you still have a ground issue with your headsets. Here's an article that might help:

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

One thing to try is to remove your headset jacks from wherever they are mounted and hold them in your hand to see if the noise is still there.

Also, what kind of battery do you have? Is it fully charged? Do you have this noise issue when the alternator is off?

Is the sound in the video the same as in your headset?
 
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