Audio Help Needed

I have the older Skyview conversion harness installation. Both the pilot, and copilot mic jacks are isolated according to the plans. My headphone jacks are not. They are grounded via the mounting, without the isolator washers. In an effort to reduce interference, and while chatting with the intercom guys at Oshkosh, it was suggested that I isolate the headphone jack from the airframe, like the mic. Apparently, not using isolation washers is quite unusual in the intercom world.

As a layman, I am not sure what to do.
First, is this going to help any with noise, or should I just leave it alone??
Next, Can I just open up the hole and install the isolation washers on the headphone jacks? These washers were included in my kit!
Do I need an additional ground wire on these jacks, now that they don't have chassis ground, and If I do, do I need shielded wire, and where would they go?

Hope someone can help. This is about 3 notches above my pay-grade, and I would like to stay out of trouble here.

Thanks. Tom

Yes isolate the jacks.
Yes you need a ground wire.
Run all wires using multiconductor shielded cable, connect shield to ground only at the avionics end. It should mimic your mike wiring.

Thanks Bob Turner

Thanks Bob,
I guess I will need to run a shielded wire through the tunnel, and up to the avionics bay. I was afraid that was going to be the case. It sure would have been nice if I would have had that info when installing the tunnel harness. Oh well!! Tom

Actually, grounding the headphone audio via the barrel (no isolation washer), but grounding the mic jack to the audio common (using the isolation washer) is not that unusual. As long as you've followed general practices in grounding audio circuits, I wouldn't think this should cause any problems at all.

The only caveat would be that I would follow the installation instructions provided by the intercom manufacturer.


However, if you want to try a different ground point for headset audio, its a simple matter to unscrew the hex nut, pull the audio jack out of the panel and run a temporary ground wire to an appropriate ground stud, and then isolate the jack and plug with some cardboard or such. Maybe you could tape it to something temporarily. Then, try a "test-flight". Just starting the engine and turning the normal avionics on should do it. I'd try it one audio jack at a time with a couple of known good headsets and someone to man the other headset.

Check out the Sigtronics SPA-4SI 4 place stereo intercom wiring diagram. Notice the difference between grounding for the mic jack and the audio jack. The instructions even say to make a 3/8" hole for the audio jack, but a 1/2" hole for the mic jack. The larger hole is so the mic jack barrel will not contact the airframe.

I also have the old harness and the jacks are not isolated. The fuel pump and the strobes have the suppression filter/capacitors. Sound quality is better than expected.

N804RV said:

The only caveat would be that I would follow the installation instructions provided by the intercom manufacturer.

Click to expand...

Just to clarify: There is more than one way to skin the audio ground cat. Sigtronics uses one way. Here another way: PS Engineering PM1200 intercomm

Either work just fine and both are installed in many, many GA airplanes. So, the answer is, given the equipment you have, what do the installation instructions say?

Most RV-12s are wired according to Van's plans and the headphone audio works just fine. But it will not hurt anything to isolate the headphone jacks during the build while it is easy to do.
Joe Gores

Great Discussion

Thanks for everyone's thoughts, and ideas. I am wired according to Van's plans. By the way, grounding the headset via the barrel to the airframe is also supported in the intercom installation manual. I had terrible noise when I first hooked it up. I was able to eliminate much of it by adjusting the side tone levels. I still had a little, but it was more prominent with my David Clark headset, than any other. In an effort to totally eliminate the issue, I contacted Van's. The first suggestion was to eliminate the music input. To be honest, that worked quite well, and satisfied my need. Later, I received additional ideas from Van's via email. One of the approaches in this document was to isolate the headset ground, but didn't give details. Apparently this will become the practice in later kits. I thought that I would try that, and see if it resolved my music input issue. But, for now, I plan to leave the music input disconnected, and fly the airplane, at least until my first condition inspection.

Help... Very Faint Muffled Audio

I really need help trying to figure out this issue. I have looked through all the threads but don't see the answer.
First off I have the Skyview conversion harness with the SL40 and Flightcom 403. My finish kit was shipped prior to 08/2011. The problem is very faint muffled audio in the headsets. This includes intercom, radio transmissions in and skyview audio.
I have tried 3 different headsets alone and together. I have removed both phone and mic jacks from the floor to eliminate the grounding issue there. I have tried changing settings in the Garmin with no improvement. However I am able to transmit to a handheld radio loud and clear.
I have also tried to pin out each wire from the jacks but I am not finding them at the AV 5000. Not clear which harness I should be checking in. The wiring drawing shows for instance GR/Wh to pin 13 but which harness for pin 13?
Any suggestions would be greatly appreciated.
Thanks

If working inside a hangar, some lights will cause lots of static. Turn them off and see if things improve.

Ray,
I am not in a hanger, yet. However I hope to move the plane to the airport after I resolve this issue. I have had the plane outside, no change. Not a static issue, more of a muffled very faint audio. All most unhearable.

Dan,
Confirm using Van's schematic for SkyView prior to 8-25-2011.
I do not understand where on the schematic you see "GR/Wh to pin 13".
Do you hear the stall vane tone warning very faintly too?
Does it make any difference if the Flightcom 403 is switched to isolate?

Joe,
Yes using Skyview electrical system shipped prior to 08/25/2011. I am looking at the headphone / microphone jack section of the drawing. It shows Pilot headphone blu-10, wh-9, Pilot mic Grn-13, orn-2. Co-pilot headphone jack, blu-12, wh-11, Copilot mic grn-13, orn-3.
These are the wires I am trying to pin out but not sure which connector I should be checking.
My wings are at the airport, so I cannot try the stall warner.
When the flight com is switched to isolate I get a loud tone in the headsets.

Dan,
OK, I see what you are talking about now. The numbers and colors are on the jacks themselves on Van's prior schematic. The headset portion of that schematic leaves a lot to the imagination. Download Van's Skyview AFTER 8-25-2011 and use that for the headsets.
The headphone and mic wires should be connected to the "OPTIONS" D-Sub on the AV-50000A, pins 24, 25, 26, 27, 28, 29, 37.
That loud tone in the headsets when switched to "ISO" makes me think that the problem is in the intercom or its wiring. Double check those wires.
There have been rare cases of harnesses having wires accidentally interchanged or on the wrong pins.

Today I checked the intercom harness and all wires pin out correctly. With all phone jacks removed from the floor and outside the plane I tried grounding the Headphone jack to the ground on the mic jack. Resulting in a loud tone, even with the avionics switched off.
I also pinned out the jack wires to the option harness as Joe suggested and they are correct.
The intercom from pilot to copilot is also very faint and almost inaudible.
Not sure what to try next.

It's very hard to trouble shoot remotely, but here are a few things to try:
Re-install all jacks.
Look at every jack from behind as you insert a plug. Make sure the little fingers that make contact don't move outboard enough to contact anything (like a sidewall).
With harness attached but power off, put an ohmeter on the ground side of each jack, measure resistance to a good ground. It should be zero.
Disconnect the harness from the intercom. With no headsets plugged in, put an ohmmeter on the harness pin for each mike input and each headphone output, measure resistance to ground. They should all be infinite.

BTW, the mike jacks are wired to the 'ring' terminal, not the 'tip', right?

Bob,
The mike jack uses the ring and sleeve terminal as per Van's drawing. I have no connection to the tip terminal.
Mike,
I have the jacks outside the aircraft so they cannot ground to the airframe. What is the best way to check ground back to the AV5000? The ring terminal has the correct blue wire called out per Van's diagram.
Not sure what infinite resistance is. I unplugged the harness and checked resistance from the headphone and mic output pins against airframe ground and I do get a reading.

Dan,
Does the volume change at all when the intercom volume control is turned?
You said that the radio transmits loud and clear. The mic audio is getting to the intercom, but it seems that the intercom is not amplifying the mic audio enough before sending it to the headsets. It is possible that the intercom volume potentiometer is defective.
On page 10 of the Flightcom 403 manual is Figure 13, a By-Pass Plug Wiring Diagram. I suggest that you make that D-Sub jumper and install it in place of the intercom. Of course the intercom between the pilot and copilot and other audio will no longer work. But you should be able to transmit and receive the radio. If then you can hear the radio OK, the problem is definitely within the intercom. Call Flightcom to discuss the problem.

D&M Dan said:

Bob,

Not sure what infinite resistance is. I unplugged the harness and checked resistance from the headphone and mic output pins against airframe ground and I do get a reading.

Click to expand...

"Infinite" means well over 100K (100,000) ohms. What are you reading (no mike or headphone plugged in)?
Mike INPUT pins.

Update

Sorry for not getting back right away. I have finally been able to spend time trying to sort through the wiring. Here is what I have done.

Went to Staples and had then print me a large copy of the wiring schematic so as I am more easily able to trace each wire.

Pinned out each lead for the Garmin SL40, Flightcom 403 and wiring through the AV5000. I can find no shorted or mixed wires as per Van's drawing.

Played with the potentiomenter for Com1. Had no effect.

Bypassed the Flightcom 403 with no change.

Reinstalled the headphone jack without the insulation washer. When turning on the master switch I immediately get a loud side tone, even without turning on the avionics switch. With the avionics switch on the volumn is much louder and controllable with Flightcom Volumn Switch now, but with the sidetone. Possibly a grounding issue somewhere? The ground wires I traced seem to be as Van's drawing depicts.

Also I do not know if this is related, but when scrolling through the Skyview setup I see 5 serial ports. Do these need to be setup?
#1 None Serial in Function None Navigation Source Display (Not Set)
#2 Dynon SV-ADSB-470 Serial in Function ADSB Navigation Source Display (Not Set)
#3 Dynon SV-XPNDR-261Serial in Function Transponder Navigation Source Display (Not Set)
#4 Garmin / Apollo SL40 Serial in Funtion None
#5 Dynon SV-GPS-2020 Serial in Function Pos 1 Nav Source Display *(Not Set)
Thanks for Helping, I appreciate the advice.

Dan,
Have you checked the stall warn vane switch? What happens when you lift the vane, any change?
Do you still have two audio problems, loud squeal and faint voice audio?
Have you tried pulling the 3 amp Audio fuse to see what affect that has?

Dan, if you still have not found the problem, try this:
Disconnect the intercom D-Sub connector from the AV-50000A. Take the back shell off from that D-Sub and remove the wires from positions 24 and 25 using the red/white tool. Jumper those two wires together. Do not put the two wires back into the D-Sub connector. Plug the D-Sub connector back into the AV-50000A. Now try the radio to see if you can hear it OK. Jumpering those two wires together sends the SL40 audio output directly to the intercom, bypassing the audio portion of the AV-50000A. If you can now hear the radio OK, then that means that the problem is either inside of the AV-50000A or else one of the audio inputs to the AV-50000A.

Dan,

Are you sure it's a side tone (mic feedback into the head phone) or is it just a loud tone? Any chance you have a grounded wire on the stall input and you are hearing the stall warning? Vans did not provide internals for modules in the control box, but on the D180 version, the audio mixer is wired to the avionics fuse before the avionics switch, so the mixer can't be turned off. With the avionics switch off the tone can't be coming from any of you avionics devices.

Here is an easy test for you...pull the stall fuse and see if the tone stops.

Mike, we are thinking alike. I had questioned the stall warning in posts 12 and 22. In the SkyView equipped RV-12, the fuse is labeled "Audio" instead of "Stall Warn", and it most likely powers the audio mixer too.

I agree that it's worth checking that you aren't hearing the stall warning. Earlier this year I installed a Garmin 420 (430 without VOR/LOC/GS receiver) replacing an Icom A210. I got a radio guy to do the wiring changes. Fired up the 420, got the audio but also a continuous tone. Naturally figured it had to result from work just done. Spent 3 hours chasing the problem only to eventually find that the stall warning switch had failed and was emitting a continous tone. Disconnected switch and all was good. The radio guy had his gear laid out on the wing and had bumped the switch, breaking it.

I've also been around the mulberry bush on isolating the jacks, but first a caveat - the guy who built my plane did his own thing and ran nearly all the wiring through a large junction box (LOTS of soldering). It will be wired differently from most, if not all other, RV12s. I was never happy with the intercom (Flightcom). Not good sound and lot of hash during first seconds of transmission, especially with passenger headset in use.

Back in June I was heading off on long trip with my son. I'd noticed the revised plans from Vans calling for isolation of both jacks - my mic jacks were isolated but not the phones - so decided to isolate phones in hope of improving audio. Disaster. No audio at all and we were leaving next morning. Quickly regrounded phones and back in business.

Next step was to instal a PS Engineering intercom. I had used them in previous aircraft and found them to be great. Installation instructions explicitly said both jacks MUST be isolated. Radio guy felt that if we wired PS Eng unit in same way as Flightcom and altered nothing else, everything should work. He was half right. Audio came up strong with phones grounded but no transmit. Contrary to instructions we removed isolating washers from mic jacks and everything is now working perfectly - best intercom/radio function I've had since buying the plane, assisted no doubt by acquisition of new David Clark One X which is a generation ahead of my old David Clark ANR.

Jack

Stall Warner Sound?

The tone could be the stall warner tone, as I'm not sure what that would sound like. But I do not have the wings on the airplane so it would not be an issue with the switch itself.
Just wondering if it is possible to run a dedicated ground from the headphone jacks to an audio ground, this way bypassing the chassis ground. Where would be a good spot to tap into an audio ground. Worth a try?
Also I removed the audio fuse but you are correct Joe this powers the mixer and that turns all audio off.

I suggest that the mic and headphone jacks be wired and grounded per Van's "SkyView-AFTER-08-25-11". Pay particular attention to the ground and shield wiring. The mic Wht/Grn wire is grounded to the AV-50000 Options D-Sub pin 37. And the center terminal of headphone jack is connected to the cable shield which is also connected to the AV-50000 Options D-Sub pin 37 (ground).

Handclutch said:

Back in June I was heading off on long trip with my son. I'd noticed the revised plans from Vans calling for isolation of both jacks - my mic jacks were isolated but not the phones - so decided to isolate phones in hope of improving audio. Disaster. No audio at all and we were leaving next morning. Quickly regrounded phones and back in business.

Next step was to instal a PS Engineering intercom. I had used them in previous aircraft and found them to be great. Installation instructions explicitly said both jacks MUST be isolated. Radio guy felt that if we wired PS Eng unit in same way as Flightcom and altered nothing else, everything should work. He was half right. Audio came up strong with phones grounded but no transmit. Contrary to instructions we removed isolating washers from mic jacks and everything is now working perfectly - best intercom/radio function I've had since buying the plane, assisted no doubt by acquisition of new David Clark One X which is a generation ahead of my old David Clark ANR.

Jack

Click to expand...

For a specific process to work, all other install requirements have to be met.....
When isolating the mic and headphone jacks, there has to be a ground source for each. If adding insulating washers makes something not work, it is likely an indicator that the installation is not wired an a manner that provides a ground at the intercom and of the wires.

If adding insulating washers makes something not work, it is likely an indicator that the installation is not wired an a manner that provides a ground at the intercom and of the wires.

Click to expand...

Agree, that is why I suggested that the mic and headphone jacks be wired and grounded per Van's "SkyView-AFTER-08-25-11". The "Prior" schematic is missing the ground wire on the headphone jack.

Stall Warner Sound Update

I am now beginning to believe the sound I am hearing is in fact the stall warner. Reminder, my wings are at the airport, so the switch is eliminated as the problem I have checked the stall warner lead to the fuselage harness where it enters the AV5000A and it has continuity. I am wondering if something inside the AV5000A is the issue. Not sure how to check it and have sent a message to Van's tech line.
I believe the sound is generated by the audio mixer inside the AV5000A but I am unwilling to open the box and void any possible warranty, to see if a solder joint is missed or loose.

Pin 6 on the fuselage connector is the control line input from the stall switch in the wing. Any time it switches to ground, the stall warning activates.

You can confirm whether you are actually hearing the stall warning tone, by adjusting the stall volume pot clockwise and listening for a volume change.

If you confirm it is the stall warning you are hearing, ou should be able to functional test the stall warning system with the fuselage D-sub connector removed from the AV-50000 box. If the tone is gone with the connector removed, then at some point in the fuselage the control wire is incorrectly connected to ground (the stall warning is activated by the wire on pin 6 being switched to ground by the stall switch). If the stall tone is then still present with the fuselage connector removed, it might be a problem in the AV-50000 box.

AV 5000 Repaired

Thought I would report back what was found to be causing the loud stall warner tone in the audio system. After bypassing the com radio from the AV5000, as Joe suggested, the radio worked properly with no tone. I was working with Sterling at Van's by email and he suggested I return the unit for testing.
Scott Mc Daniels I believe tested the unit and found a failed MOSFET in the stall warner circuit.
I have reinstalled the unit and as suggested ran a dedicated ground wire from the headphone jacks back to the intercom ground.
Fired it up and with a little adjusting of the volume and squelch things seem to be working as advertised.
Thanks to all here and at Van's for the assistance. Off to the airport finally.