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Touch'n'oops
24th Sep 2015, 12:40
Hi All

Has anyone experienced a electronic whine coming through their headset once connected to an aircraft's jack? It gets worse when I use intercom, the other pilot can also hear it. I tried adjusting my mic gain to no effect.
This wasn't a problem on the A320, but A380 it is.

I know a lot of whining goes on the flight deck normally, but the source isn't us pilots this time. :E

I would be grateful for any suggestions. Btw, I'm using a LightSpeed Mach 1.


Thanks
"Roll the puns!!!"

EEngr
26th Sep 2015, 04:15
Any adapters between the headset plugs and flight deck jack?

Touch'n'oops
26th Sep 2015, 13:14
Yup, using the Boeing to Airbus adaptor. I also used this on the A320 before the 380. Could grounding be an issue?

EEngr
26th Sep 2015, 16:17
Could grounding be an issue?

Grounding/shielding is one thing that crossed my mind. I'm not familiar with the Airbus electronics well enough to know if there was a subtle change between the 320 and 380.

Borrow another adapter to see if an internal (in the adapter) connection is loose or wired differently.

JRBarrett
26th Sep 2015, 16:38
I do avionics maintenance for a corporate flight department. One of our pilots had this same issue with a Bose ANR headset. In testing, I found that the noise would vary in intensity with head position, getting especially loud when the headset was brought in close proximity to a circuit breaker panel on the sidewall next to the pilot seat.

It turned out that the shield had broken inside the cable going to one of the two earpieces, causing the unit to pickup radiated noise from the aircraft wiring. The problem was actually worse when the headset's noise-canceling feature was turned on - probably because the induced noise was being amplified by the ANR circuitry.

I'd suspect a ground/shielding problem. Either in the headset itself, or in an associated adapter.

Uplinker
27th Sep 2015, 12:51
I was an electronics engineer myself before flying, and I would echo what Engr and Barret suggest.

Also, I assume you have checked other headsets in the same socket you are using, and your headset in other sockets? It is unlikely that the A380 socket has been miswired by the manufacturer, but not impossible.* It could also be a faulty ACP on the aircraft, so try using your headset with other ACPs.

When you have discounted by substitution all other possible reasons for the noise then the cause must be your headset, and you can start to work through that.



*We were once using an airship for some TV work, and one of its (Porsche flat 6 piston) engines was occasionally misfiring. To cut a long story short, it was found that the coaxial cable feeding the ignition system had been cross-wired on the faulty engine - the outer screen was carrying the signal and the inner conductor was connected to earth. This is the wrong way round and it meant that external interference was affecting the ignition signal, instead of it being shielded from it by an earthed outer screen.

Touch'n'oops
28th Sep 2015, 08:52
Thank you for all the replies.

I have tried in the headset in multiple A380s the older aircraft seem to have less of an issue, but this is not consistent. I have another adaptor from long ago, which I can have a crack with.
The headset doesn't have ANR, but it does have a box which a phone can be plugged into or listen to music. This requires a small watch battery to power.
Additionally the cabling of the headset looks simple, so I doubt it has any shielding its self. Is it possible to add some sort of wrap?
I do notice a quiet background noise when I connect the headset through the cockpit speakers, which stops when I pull the headset out.

I have also used other types of headset and no sound issues with those.

I'm not flying for a week, but I will give the other suggestions ago and let you know.

Thanks again.

EEngr
28th Sep 2015, 16:56
The headset doesn't have ANR, but it does have a box which a phone can be plugged into or listen to music. This requires a small watch battery to power.

Just for fun, try changing that battery. If it gets low, some of the internal logic might get a bit wonky and couple some noise into the mic circuit.

I dug up the manual on this unit. There appears to be a few DIP switches inside the control box. The manual wasn't too clear on the setting of the 'power' switch (turn off when directed to by a technician). That might be worth investigating. I suspect it selects an external (cockpit) mic power source on or off. But I'm not certain.

Additionally the cabling of the headset looks simple, so I doubt it has any shielding its self. Is it possible to add some sort of wrap?

Not easily. The critical part of shielding is how it is connected to the comms panel ground/shielding. Not something easily done without major hardware hacking with tiny little wires.

I do notice a quiet background noise when I connect the headset through the cockpit speakers, which stops when I pull the headset out.

I suspect that there may be some sort of interconnection between the headphone circuit shield or common and the mic shield or common that involves the adapter and/or the wiring inside your headset. Noise picked up on the headphone side gets coupled to the mic input, which is much more sensitive. What happens when you plug the headphone jack into the adapter but leave the mic unplugged (not useful for operation, but it could be of diagnostic value). An electronics tech with an ohmmeter could check out your headset and adapters and identify any possible interconnections (or broken shield paths) inside. Someone at Airbus customer engineering should be able to provide a technical level specification of what should/should not be interconnected.

BARKINGMAD
29th Sep 2015, 23:26
I presume you've eliminated the AC buzz which occurs on some aircraft, with some types of mic, when the mic is too close to the heated winscreen(s) and picks up the heating AC by induction? :)

EEngr
30th Sep 2015, 01:56
the AC buzzThat's almost certainly what it is. Perhaps not from the window heat. But the 'buzz' you get from inductive pickup would be a whine on an aircraft since it is a multiple of 400 Hz rather than the more familiar 50/60 Hz buzz. Window heat is particularly bad if it is a 'chopped' waveform when it is not on 100%.

Here's an idea (cheap and non-destructive): Touch'n'oops (http://www.pprune.org/members/59210-touch-n-oops), obtain one or two split ferrite core filters. The kind that can be snapped over a cable. Like this:

https://images-na.ssl-images-amazon.com/images/I/61o7Pw9-umL._SL256_.jpg

Snap one over the mic cable (before the adapter) or one on each cable (mic and headphone). Once through is good, a couple of wraps is better (like the photo) if length is available.

Touch'n'oops
8th Oct 2015, 08:01
Thanks for all the replies

On the last flight I tried my spare adaptor, no change. Moving about the flight deck with the headset didn't cause any change in the interference.

EEngr:
I have had a play with the dip switches to no avail and also tried the ferrite core with the double coil and all sorts of ways, no joy.
I'll try sniff out a guy with an ohmmeter and find a new battery. The issue only arose when I connected to the A380.
Airbus engineer for advice... haha... haha... These guys don't even get back to the owners of the 380s in a timely manner!!!

BARKINGMAD:
I have already tried switching off the windshield heat, no effect. Thanks for the suggestion.


BTW, the 380 has unique generators as they are variable frequency, could this play a part?

Thanks for all the suggestions.

Touch'n'oops
16th Oct 2015, 06:02
Hi Gents,

Just did a flight and found that if I disconnect either of the jacks from the adapter the noise goes away. I did this by listening to the speaker with intercom selected.

Eng you suggested there is a misgrounding somewhere. As the cables have been replaced recently would you think it is in the headset's junction box?

Cheers

EEngr
18th Oct 2015, 04:23
Eng you suggested there is a misgrounding somewhere.

I don't know if I'd call it a "misgrounding". But the headphone and microphone circuit grounds could be tied together. Your test appears to indicate that the "loop" is inside the headset itself as opposed to within the adapter.

The next step I'd try would be to find or have built an isolating device. This would be a small enclosure with a plug and jack that would 'break' the electrical continuity of the headphone circuit. Here is an example of a home-brewed device* (for a different but related application):

Application Note: DXD Configuration File Excerpts (http://www.qth.com/topten/apnote9.htm)

If you trace the schematic, you will see that there is no electrical path from the input plug to the output jack. The signals being coupled through the transformers (magnetically). There may be commercial units available with the appropriate plugs/jacks. There are bulkier units with screw terminals and larger enclosures that are not suited to flight deck use. There may also be dual jack to XLR5 adapters made with isolation transformers built in, but I am not familiar with any.

*If your headphones have a mono jack, only 1/2 of this circuit is needed.

Metro man
18th Oct 2015, 10:29
Is the headset on the approved list ? We can use personal headsets but the model must be on the list.

MD83FO
18th Oct 2015, 16:48
I do get a sound on my airbus telex 850 but only on some airplanes when the intercom is on.
Its the same background chord you hear on the frecuency when some boeings transmit.

Uplinker
21st Oct 2015, 23:03
@ Touch'n'Oops; Sounds to me as if there is a mis-wire somewhere; i.e., in either the mic or earphones circuit, the earth and signal connections might have been reversed.

This reverse could be in either your headset or your adaptor.

PM me if you like and we'll talk about how to resolve this.