Audio feedback when talking on KMA 26

[JRHogancamp]

Hi all! I have a 1983 Mooney with a King KMA 26 audio panel. Whenever the headsets transmit audio and the engine is running, either by me or passengers speaking or by the radios picking up transmissions, there is a slight high-pitched whine. The high-pitched whine gets slightly louder as the transmission ends and the headsets stop transmitting audio. Essentially, imagine that there's always a tiny mouse going "eeeeeeee" in the background whenever there's a transmission. This whine does not happen when I have bluetooth going through my headset--the bluetooth is via the headset and does not use the audio panel. This whine also does not seem to happen when the plane engine is not running, i.e. sitting in the cockpit with the electronics on but not cranked. Anyone ever encountered this? I've no idea what could cause it. Thanks!

[carusoam]

Assumption 1: Everything ever encountered has been covered here before...  

Finding it...  or describing it so somebody else knows what you are talking about is the next step...

1) You have a squeal in your headset...

2) happens during transmission on the radio...

3) Engine has to be on

4) Blue tooth connection when used has no whine...

Hmmm...

Sounds like you may have a grounding challenge...

Look to see what is plugged in the cigarette lighter socket... USB chargers suck for causing noise in the audio system...

 

PP thoughts only, not an avionics guy...

Best regards,

-a-

[LANCECASPER]

13 hours ago, JRHogancamp said:

Hi all! I have a 1983 Mooney with a King KMA 26 audio panel. Whenever the headsets transmit audio and the engine is running, either by me or passengers speaking or by the radios picking up transmissions, there is a slight high-pitched whine. The high-pitched whine gets slightly louder as the transmission ends and the headsets stop transmitting audio. Essentially, imagine that there's always a tiny mouse going "eeeeeeee" in the background whenever there's a transmission. This whine does not happen when I have bluetooth going through my headset--the bluetooth is via the headset and does not use the audio panel. This whine also does not seem to happen when the plane engine is not running, i.e. sitting in the cockpit with the electronics on but not cranked. Anyone ever encountered this? I've no idea what could cause it. Thanks!

Sounds like feedback. Are you sure that your cabin speaker is not on also?

[Bartman]

Problems I have personally encountered causing noise

1. Alternator
2. spark plug wires
3. Multiple USB chargers in the cigarette lighter

[JRHogancamp]

@Bartman Thanks for the reply! I suspect it's the alternator. Any suggestions about how to troubleshoot and/or fix the issue?

[carusoam]

Alternator noise is often caused by burned out diodes...

Diodes often leave a check-me sign on them...

Find the diode bridge in the voltage Rectifier... the AC to DC bridge...

PP thoughts only not mechanic...

Best regards,

-a-

[Baker Avionics]

Check the Alternator filter circuit, if installed, miscellaneous ground wires in the engine compartment that are just cutoff and are running into the cabin area.