PA17-79 ANC - Having Problems

[Mad Girl]

This is NOT another "Which Headset" thread.

I've been through 3 sets of PA17-71's (in a year) and am currently trying out the PA17-79 as I keep getting a persistent problem.

After approx 30-40 minutes of a flight I get a very high pitched electronic squeal in my ears and the only way to stop it is to turn the set to passive.

At first both Pilot Communications and I thought there was a fault with the headset and they exchanged it with no problems. Then... when the same thing happened with the new set, we thought it could be an intercom issue with the airplane, so I then swapped my lessons around 3 - 4 different PA28 Warriors. Same thing.

Pilot upgraded the PA17-71 to a PA17-79 which I immediately charged up, and tried this week end - guess what - same problem.

Are there any headset electronic "experts" out there who've got any bright ideas??

Pilot sell 1000's of this type of headset and have done for years...so we just don't understand what could be causing the issue.

and....I just have to say that Pilot communications have given me absolutely fantastic customer service throughout this little experience - nothing has been too much trouble :ok:.

PS - I don't want to give up with them because, quite frankly, the headset is the most comfortable I've tried - no clamping, no head aches.

[IO540]

I bought the PA17-79 a few years back and it's a piece of junk.

It's a very long story, running to dozens of emails and faxes, and eventually I was able to return it to where I bought it from (a U.S. mail order outlet) for a refund. In the process I discovered that every advertiser was putting out bogus attenuation claims on this headset - 44db I recall - following misleading figures from the manufacturer. I have graphs of my actual headset showing a far lower figure and a confirmation from the mfg that this headset is in spec.

Mine whistled a little but the worst bit was that the attenuation was poor.

Then I did a test of a load of headsets, bought a Bose X and never looked back. Just make sure you get one of the current model ones; Bose were selling duff mikes for a few years and the amnesty for getting them exchanged has now expired. They still worked OK, better than most headsets in fact, in most (but not all) intercoms.

[michaelthewannabe]

I'm no expert on headsets, having only just started flying, but I do know a bit about acoustics and audio electronics. It sounds like a flaw in the noise-cancelling electronics. But the fact that it does it on different headsets and different aircraft is weird.

Do you notice the squeal from televisions (the old cathode ray sort, not flat-panel ones)? If so, does it sound anything like that?

Are you quite young? Perhaps you've got exceptionally good high-frequency hearing? High-frequency hearing deteriorates with age, from late teens onwards IIRC.

Are there any controls on the headset for the electronics? If so, does the squeal persist at different settings?

The electronics used for active noise cancellation is intrinsically prone to causing a whistle or squeal if it's incorrectly designed or has a manufacturing fault, because it's a feed-back system. Given bose-x's comment about whistle, maybe it's just a design flaw that most customers don't hear because their high-frequency hearing is poorer than yours.

FWIW, I've just bought a Clarity Aloft in-ear set - but I haven't been able to use it yet because of this bloody weather! I'll let you know what I think of it when I've tried it out.

[Mad Girl]

Hi IO540,

Well........ for the 30-40 minutes that they work properly, I DON'T have any issues!!

Sound quality is good - everything is much clearer.


So... I've got no problems with Pilot who are quite prepared to get me a refund, with no quibbles, if we can't resolve the problem - but I WANT to keep the headset and find a cure, because I like it.


I'm more interested to know if anyone's enountered any compatability isses with other headsets or can think of something which could cause the almost "timed" problem in the first place.

[Mad Girl]

michaelthewannabe said
Are you quite young?
I wish !!! :D
I do have very good hearing and can hear sounds on a high frequency that others (my other half) can't, but he's used my headset on a trial lesson and it did it to him too.

And this noise is loud - makes me squirm!!!!

Are there any controls on the headset for the electronics? If so, does the squeal persist at different settings?
Yep - It's got individual volume controls for each ear cup and a stereo/ mono switch on the back of the volume control. The control is half way down the cable.
I have tried turning the volume up or down before, and playing with the volume and squelch on the airplan's intercomm, but with no change.

The only solution is to turn the active bit OFF.

[michaelthewannabe]

Have you tried turning the active switch back on again, after turning it off? I've seen circuits (especially feedback circuits dealing with noise) that seem to work fine, but over a long period of time can subtly build up an oscillation (e.g. a squeal) that eventually swamps the system - but resetting them puts it back to square one.

[BeechNut]

And here I thought this was a thread about the Piper PA-17 Vagabond with its engine uprated to 79 hp...a buddy in fact just finished restoring a PA-16 Clipper, lovely little aircraft.

[Mad Girl]

Have you tried turning the active switch back on again, after turning it off? I've seen circuits (especially feedback circuits dealing with noise) that seem to work fine, but over a long period of time can subtly build up an oscillation (e.g. a squeal) that eventually swamps the system - but resetting them puts it back to square one.


Pilot Communications put one of the headsets on test for 8 hours without the fault developing again, which is why we thought there could be an incompatability/interference issue somewhere in my flying environment.

I'm only a student and tend to have my hands full most of the time :O so "stop the noise (distraction)" and get on with what I'm doing has always been the priority.

I have to admit to not having tried a simple on/off yet. I'll ask my instructor to humour me next time I'm up, and fly the airplane whilst I "twidddle".

Should a straight on & off do the trick or should I try off, wait a minute, and back on ??

[IO540]

IME most training planes have poor intercoms. Many don't have an intercom - the headsets are all (presumably) wired up in parallel and you can get interference problems with a mixture of types.

I am an electronics design engineer too, been doing it for over 30 years, but have never really gone into avionics audio - the way it's wired is really weird at times.

The 17-79 was a comfy headset, but the attenuation was poor. The ANR feature contributed very little. A Bose X is a complete revelation in comparison, and their current mike is a further revelation over the previous one (presumably due to better noise cancellation). However, despite recent drops, it's about 2x the price of the Pilot one.

[michaelthewannabe]

Should a straight on & off do the trick or should I try off, wait a minute, and back on ??

Flick it off and on, quickly.

If that doesn't work, switch it off, wait a few seconds, then turn it back on.

If that doesn't work, unplug the headset and plug it back in.

If that doesn't work, do the same but with a pause before re-plugging.

If that doesn't work... I'll be confused (not an uncommon state, I might add).

good luck!

[michaelthewannabe]

Many don't have an intercom - the headsets are all (presumably) wired up in parallel and you can get interference problems with a mixture of types.

That's a very good point. I'd expect that the headphones are passively in parallel on old spamcan intercoms, but with individual active buffering on modern intercoms like a unit a pilot shop might test something on.

Does the problem always occur with the same instructor, or with instructors wearing the same type of headset? If so, and if my last suggestion doesn't work, perhaps you could try to get your instructor to wear a different headset for a lesson?

[Mad Girl]

Hi michaelthewannabe

Yes, I'm normally with the same instructor, or with an instructor with the same headset brand. Although some have the passive David Clarkes and one (my main instructor) has done the mod to convert his passive set to active.

But a couple of weeks ago I flew with someone who had a passive Peltor and had the same problem at about the same 30-40 minute mark.

[michaelthewannabe]

Fine, I guess that discounts the theory that it depends on what other headphones are plugged in to the intercom. I hope that switching it back on or plugging it back in sorts the problem!

[Mad Girl]

Michaelthewannabe said
Flick it off and on, quickly.

If that doesn't work, switch it off, wait a few seconds, then turn it back on.

If that doesn't work, unplug the headset and plug it back in.

If that doesn't work, do the same but with a pause before re-plugging.

If that doesn't work... I'll be confused (not an uncommon state, I might add).

good luck!

Me again - Bad Wx stopped play over the last couple of weeks, so I went up again yesterday. :D

My partner took the headset for a trip with someone before my lesson, just under an hour, and the headset was fine the whole time.

I went up for 1 1/4 hours and I got the same high pitched squeal as before but at about 1 hour 5 mins (Oh good - 20-30 minutes more reprieve!!).

I turned it on and off quickly, twice, with no effect and then turned it off, waited 3 seconds and back on again and the noise was gone - Option 2 on your list.

Could you write me an "engineering" lingo explanation of what you said it could be re: the oscillation, so that I can e-mail Pilot who can give it to their engineer. Then you can use as much technical language as you like because you won't be trying to explain it to a totally NON electrical engineering pleb.:O

PM me if you don't want to post.

Also.....As I got 20-30 minutes more time before the squeal this time - could electronic circuits need to be run in?? i.e. warmed up a few times.?? :confused:

Thanks :ok:

MG

[IO540]

The whistling noise could be either a problem with the noise cancellation circuit in the headset (this uses a feedback loop and can thus go unstable) or it could be due to the aircraft intercom not liking the impedance of the headset.

[michaelthewannabe]

The whistling noise could be either a problem with the noise cancellation circuit in the headset (this uses a feedback loop and can thus go unstable)That's exactly my suspicion.

or it could be due to the aircraft intercom not liking the impedance of the headset.It would be very surprising if the input impedance of the headphone changed significantly when the active circuit is turned on. So I think this is more unlikely.

Does the headset have a battery, or does it draw power for the active circuit from the intercom? If the latter, then that could cause it to be dependent on the combination of headset and intercom: if the intercom isn't supplying quite enough welly, the active circuit might malfunction and go unstable. Or it might even be an oscillation on the power supply from the intercom - rather unlikely, though.

Mad Girl: Well done on getting into the sky (better than I've managed recently!). And glad you've found a fix. The rapid switch off/on probably doesn't work, because the circuit stores a bit of residual charge and needs to be switched off for a couple of seconds to actually power down, and restore the circuit to its starting condition.

I can only speculate at the cause, but my best guess is this...


There appears to be a fault in the design or the manufacture of the active noise reduction circuit, which causes it to go unstable after a sustained period of time in the presence of normal cockpit noise levels and usage. This instability manifests itself as an oscillation high in the audible frequency range (probably around 10-18 kHz from the description), gradually increasing in amplitude, and taking 60-90 minutes to become audible. Powering-down and re-powering the ANC circuit clears the fault. It might be dependent on the type of intercom, though this is less likely as the problem occurred in a number of different aircraft.


Also.....As I got 20-30 minutes more time before the squeal this time - could electronic circuits need to be run in?? i.e. warmed up a few times.??It's very unlikely that it needs to be "run in" (regardless of what audiophile loonies say about their hi-fis). But the development of the squeal is probably dependent on various factors, like the sound level in the aircraft, or the temperature, or any number of other random things. So it's not surprising that it might take longer one day than another.

It'll be interesting to find the cause, if Pilot set their engineer on the case! Happy squeal-free flying.

mtw

[IO540]

ANR headsets are powered; one can't draw enough power from the audio signal.

I agree the whistling is most likely a feedback issue with the noise cancellation circuit (which uses a mike inside the earcup, wired to achieve a null sound level pressure inside the earcup with zero audio signal) but

It would be very surprising if the input impedance of the headphone changed significantly when the active circuit is turned on. So I think this is more unlikely.

this is still possible because e.g. presenting an excessively capacitive load to a badly designed audio amp could make it go unstable.

But, as I've said before, I think the 17-79 is a crap headset in terms of performance.

[Lister Noble]

I've used the 17-79 headset in a variety of modern and old aircraft over the last two years ,as has a pal of mine.
We have had no trouble and think they are brilliant,you can pay a lot more just for a name.
Lister;);)

[Grilla01]

I've just had the same problem with one of my 17-79s which till now worked well.

There's a painfully loud, medium-frequency, feedback-type squeal any time the ANR is switched on.

The problem IS NOT related to the intercom system as the headset squeals when disconnected; the mic isn't part of the active feedback loop causing the trouble because the problem still occurs with the mic unplugged.

I've sent it back to Pilot Comms to look at with the comment that the problem is potentially a flight safety issue because the noise is loud enough to be debilitating.

I wonder whether it's worth continuing this thread for flight safety reasons?

[IO540]

Like I said earlier, that headset is a particular piece of c*** :)

But many of the "cheap" headsets are, unfortunately.

[Jhieminga]

I've used a Softcomm ANR headset for a few years that squealed when some people put it on. My guess was that it was an improper seal that let unwanted noise in causing a feedback, it happened particularly with people with a relatively small head size.

In the end though the explanations given above go to the root of the problem: cheaply designed electronics. I've had a lot of fun with the headset mentioned above but I could tell that it wasn't all that good (with ANR on there was a persistent hiss but the overall sound quality was pretty good, and with ANR off it reverted to a cheap headset with lousy sound quality). It did what it said on the box but I've now switched to a David Clark with ANR and that's a lot better.

[IO540]

Hiss is common in crappy ANR headsets. I have a £80 Sony headset for walkman type uses, or for wearing on an airliner to keep the noise down. It whistles too. And my GF went for one of the free trials of the £300 Bose ANR headset which they are trying to flog to airline passengers etc; it was very comfy but whistled too and was sent back, and Bose said nothing whatsoever...

[Zulu Alpha]

Its worth checking the seal. If you wear glasses this can affect the seal against your head/ears.

I found my DC ANR headset very variable, but using my hands to squeeze it onto my head always removed the problem.

In the end I found it best to have the headset volume control turned right down and the radio turned right up. This might cause comments from your instructor unless he also has a volume control on his headset.

The ANR circuits use a small microphone somewhere to pick up the ambient noise and after inverting this, feed this into your earpiece where it is supposed to cancel the ambient noise that you hear. Sometimes this system can give you feedback, particularly if the microphone can pick up the noise from the headset speaker. Clamping the headset on your head and turning the headset volume down both reduce this.

If this doesn't work, then sell them and get Bose which are great. A better and cheaper option though is the Clarity Aloft system. Completely passive and better than ANR, but you do have earplugs in your ear.

[Grilla01]

I think we're all talking about different problems here.

The uncontrolled acoustic or electronic feedback I described in my post is definitely a fault as it is producing a deafening (almost literally!) squeal and as such could be a safety hazard. The problem has nothing to do with faulty seals or any external factor.

I don't agree completely with IO 540 as the headsets have produced several years of good service in my Bulldog and do give good noise cancelling; I like the fact that they don't use a separate box to contain the ANR circuit although they are heavier as a consequence.

I'll report back on Pilot's response to the problem!

[Agcat164]

I see Mad Girl and others had squealing problems with the pilot Pa 1779.
Yup same deal here with this one of my friends, identical to Mad Girl's issues. Sounds like the manufactures haven't quite got it right. My view, spend the money to protect your hearing. You can't get it back. Buy a Bose, it is the best that i have come accross so far. I have tried most.