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Intercom Volume Low After GTN 650 Install

M

MountainU2

Member
Hi All-

I?m a new RV owner. Bought my RV-6 from a great guy in FL, and he installed a GTN 650 and G5 as part of the buy. I wanted to be able to fly RNAV approaches if needed, and the panel was all steam previously, though the plane was IFR capable. I love the setup, but there?s a problem.

I have a new Sigtronics 400SN Intercom that the previous owner was kind enough to supply when we realized that the intercom volume was low. At first, that seemed like at least an improvement, but I think now it was really just wishful thinking.

I use a Halo (love it), and when I fly with a passenger, I give that to them and use my old DC non-ANR from the Air Force days. It works...well enough. But when the passenger plugs in a Bose ANR or similar, they can barely hear me unless I yell. I?m going to buy another Halo, but when somebody wants to fly with their A20, I know this will be an issue.

Any thoughts? The owner suggested the GTN wiring harness might need to have a resistor installed. I?m sure I could figure that out, but before I go too far into anything, I wanted to ask the brilliant minds of the VAF forum.

Thanks for reading, and in advance for any suggestions.

Keith
RV-6 N91CN
KLHM
 
Some of the low cost head intercoms don't work very well if you intermix headsets.
I suggest trying two of the exact same and see what happens.
If the problem is still there, you could have a grounding issue caused by a wiring error.
 
Bose cause all sorts of problems at work. Our jets have Sennheiser as fitted sets. If guys use Bose, I can't hear them. I guess it is different attenuation and maybe different impedances etc.

Get similar in our 7 when my mate uses his Bose against my DC Pro X
 
Maybe, but my buddy?s telex headset had the same issue. I?m fairly sure it?s my airplane, though I wish I could believe otherwise. :)
 
Did you try setting both headsets to mono? I don't think the Sigtronics intercom is stereo.
 
I believe the Headset jacks are either wired for stereo or mono and the setting on the headset has to be set to coincide if there is stereo/mono switch (most ANR headsets offer you a choice in the dipswitch settings). Might even be a switch setting in your intercom or wired as either one or the other.

Also make sure the GTN650 configuration setup is set correctly-to many possibilities to mention without knowing more on your equipment.

Lots to check before getting into wiring.

Jim
9A flying since ?13
 
MountainU2 said:
Uhhhhh... No I did not... Never even occurred to me. I?ll give it a shot when I?m home this weekend! Thanks!
Click to expand...

That's was my first thought as well. My experience is that stereo headsets don't tend to work with mono intercoms unless you switch them to mono first.

If that's not the issue, have somebody help you check the wiring. Intercom wiring can be finicky and has to be correct or weird things will happen. The reason for the helper, is that you may not be able to see the forest, because all the trees are in the way. :D In other words, it's sometimes hard for us to see our own mistakes because we are too close to the problem. A new set of eyes will usually see the issue right away.
 
rleffler said:
That's was my first thought as well. My experience is that stereo headsets don't tend to work with mono intercoms unless you switch them to mono first.

If that's not the issue, have somebody help you check the wiring. Intercom wiring can be finicky and has to be correct or weird things will happen. The reason for the helper, is that you may not be able to see the forest, because all the trees are in the way. :D In other words, it's sometimes hard for us to see our own mistakes because we are too close to the problem. A new set of eyes will usually see the issue right away.
Click to expand...

It wasn't one of my recommendations because this would cause audio to only be heard on one side of the headset, which I assumed would have been mentioned as part of the problem, but it is worth confirming.
 
Good points. To be clear, the problem is only the intercom volume. Radios are loud and clear, but even with the intercom at max volume it’s hard to hear the other person talk.

The new intercom is the same type as the old one, but an updated version. It’s a Sigtronics SPA 400N. Same slot on the panel, same wiring harness, so it was a simple one-for-one swap. I didn’t have to do any wiring.

I installed the new IC hoping it would fix the volume issue, but I don’t think it made much of a difference, so now I need to try other solutions. The previous owner is certain that prior to the GTN650/G5 upgrade, the intercom was plenty loud.
 
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MountainU2 said:
Aw, crud. After a brief googling, I found the installation manual. Therein is the following paragraph:

?It may be necessary at this time to adjust the SCI unit mic output to the aircraft radios. A small adjustable potentiometer is provided inside the unit for this purpose. It is accessible through a hole in the side of the SCI chassis. It is marked ?Mod. Adj.?, and can be adjusted with a small blade screwdriver. In the event of over- modulation (garbled) or reports of weak transmissions over the aircraft radio, an appropriate adjustment can be made. Clockwise rotation increases the output level to the aircraft radio mic input. Counter-clockwise rotation decreases modulation level. This adjustment sometimes needs to be made after the initial installation of the intercom or if a new radio is installed. (The output is set for unity gain at Sigtronics).?

I?m guessing this is the fix. I?ll report back once I get home and try the adjustment.

Potential lesson learned: RTFM.
Click to expand...

This should have no influence on the intercom performance when you talk between one headset to another. It is only related to performance when transmitting on the radio.
 
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