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todehnal

Well Known Member
Wow!! I can't believe how noisy the intercom is. With the SL40 turned off, and just the intercom on, the noise is very annoying. I found that when I shut the cooling fans down, it gets quieter. It is also quiet when I break squelch, and talk on the intercom, or when I push the transmit button. As soon as the squelch activates, here comes the noise. So, I started troubleshooting. I found that the nose is effected by the cooling fans. If I interrupt the fans, the noise reduces. But, as soon as the fans start revving up, so does the noise. Also, the noise is not sympathetic with the volume on the intercom. That volume has no effect on the interference. Anyone else have these issues, or is it just me?? By the way, I am using David Clark headsets. One last thing, if I set the headsets to mono, instead of stero, it is better. I sure hope someone has some ideas!!. I sure hate headset noise!!............Tom
 
Your symptoms are typical if there is a problem with the aux. music input connection.
The fading in after squelch closes is the music mute function deactivating (it is active, even if no music is playing).
 
When I first fired-up my SV I was extremely disheartened by the various background noises coming through my headphones. By tweaking the multiple volume pots on the AV-50000, I was able to get things balanced out relatively nicely and quietly (at least in my garage -- we'll see how well it sounds when I test fly it). So don't give up yet!

BTW, I discovered that a nearby overhead fluorescent light in my shop (with a buzzing starter) was inducing a noticeable background hum in my active D/C headsets. Took a bit of sleuthing to figure that one out!
 
rvbuilder2002 said:
Your symptoms are typical if there is a problem with the aux. music input connection.
The fading in after squelch closes is the music mute function deactivating (it is active, even if no music is playing).
Click to expand...

Thanks Scott! This seems very logical. Now, do you have any thoughts about a solution? I would even consider eliminating the music input, if I could get rid of this noise. I just need to know how to do it. Perhaps I damaged the music jack when I installed the harness.

Thanks for your thoughts...........Tom
 
My system was all quiet until I plugged an ipod into the music input for the first time. I thought I was in the amazon rain forest at night time until I unplugged it.:eek:
 
Is the music input jack connected to ground locally or isolated from ground with insulating washers? Less noise will be picked up if the jack is isolated from the airframe and the coax shield or a separate wire is used to connect the jack barrel directly to the intercom. The trouble with using the airframe to carry audio signals is that the airframe also carries current from other devices. When the audio signal gets amplified, so too does the noise.
Joe Gores
 
Audio noise coming in through the music input is very common, and happens on certified airplanes as well. The audio ground is not isolated on the music player devices, so you end up with an audio frequency ground-loop that injects noise into the audio amplifier from the music input.

The only sure-fire way to fix it is to use an audio isolation transformer to completely isolate the music input while allowing the signal to pass through. You need one transformer for each channel (left and right).

A part that works well is a Tamura T1104 audio transformer. You can buy them at Digikey.

Dean Wilkinson
AeroLEDs LLC
 
I have somewhat similar problems, and have no music jack problems, since I never hooked up the jack (I don't want or like music while flying.)

This intercom leaves a lot to be desired. Either my wife can't hear me or I can't her or both can't hear the other. If I reduce the squelch break setting, we get all the flying noises. I've tried with three different headphones.

The squelch circuit seems to be too sensitive and has a notch type kick-in - getting that sweet spot is impossible for me. Adjusting it in flight is an exercise in futility. We do a lot of yelling back and forth at each other, and we're not even having a fight.....

Bob Bogash
N737G
 
todehnal said:
Thanks Scott! This seems very logical. Now, do you have any thoughts about a solution? I would even consider eliminating the music input, if I could get rid of this noise. I just need to know how to do it. Perhaps I damaged the music jack when I installed the harness.

Thanks for your thoughts...........Tom
Click to expand...

When dealing with problems related to low level audio signals that get amplified, it can be a challenge.
Most likely some type of EMI is getting induced into the wiring for the music jack. The first thing to do would be confirm that by disconnecting the two music wires that feed into the back of the intercom and confirm that clears up your noise (you should be able to confirm which pins by referring to the install document that came with your intercom, or look for it on Flight Coms web site)
 
This Is The Plan

rvbuilder2002 said:
When dealing with problems related to low level audio signals that get amplified, it can be a challenge.
Most likely some type of EMI is getting induced into the wiring for the music jack. The first thing to do would be confirm that by disconnecting the two music wires that feed into the back of the intercom and confirm that clears up your noise (you should be able to confirm which pins by referring to the install document that came with your intercom, or look for it on Flight Coms web site)
Click to expand...

Thanks Scott. That really sounds like a terrific isolation method. To be honest, if that works, I may leave it disconnected until a later date. Quite frankly, I have never had a music input in an airplane, and I don't think that I would miss it. Building E-AB, certification is not an issue, and I am getting anxious to get my 12 flying. I will try that today, and report back.........Tom
 
Most of my flying is solo so I just use the Bose Aviation X aux input jack for my music. Sounds great. The music jack in my 12 seems to crackle a bit, so this was an easy solution.
 
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