Menu Sign In Contact FAQ
Banner
Welcome to our forums

Electronics Advice

There seems to be a few electronics experts here and hopefully one of you will be willing to give me a little bit of advice.

I have two very good headsets which I am very happy with. As I mainly fly with just one passenger or other pilots (who have their own headsets) having two good seats is perfect.

However occasionally I'll have two passenger which involves one of them using one our of group's headsets which to be frank are old junk which is pretty much falling apart. Nobody really wants to use them, much less put the mic close to their lips.

A few years ago I saw someone recommending a really cheap new headset from ebay (presumably made in China). It was only €50 brand new with a bag, so I thought I'd give it a try on the basis of the recommendation, but didn't really expect much.

However I was rather surprised. It was well designed (seemed to have ripped off a Schneider design) and (passive) noise annunaction was very good. Sound quality while listening to others was perfect. However it has one fatal flaw making it useless.

When the person using the headset speaks everyone else hears them like they were talking through a long pipe. This was on the intercom; I didn't try any transmissions with it. To the person wearing it, the side tones that they hear themselves as they speak themselves also sound like they are speaking through a long pipe.

My conclusion is that the microphone is what's wrong. It's a pitty, as it's the only thing letting down this budget headset and otherwise it would be perfect for the occasions when I've a second passenger. (Brand new, clean, comfortable, good noise reduction and good sound quality).

I tried to see if I could remove the microphone and buy a more expensive one, but it appears that the wire runs all they way from the ear cups right to the microphone itself (ie it isn't plugged together so I can't just unplug it and plug in a new one.).

This is what it looks like when I remove the back casing.

Could anyone advise if it's practical to replace this microphone with a new one? I don't know much about electronics but I do have a soldering iron and some solder. (Not that I've ever done a huge deal with it). Is it simply a case of breaking off the existing connections and put a new microphone in and soldering the wires back onto it?

If so, how would I know what sort of microphone I need to get, and could someone point me to a place where I could buy one?

Or is this even a solution? I am on the wrong track thinking it's the microphone or would there be a whole load of other electronics that need to be replaced in the ear cups?

I'm really out of my league on this. Given the initial cost I'd have no problem in just throwing it away, but it seems like it can't be a big job to make this headset suit it's purpose very well.

Thanks Colm

EIWT Weston, Ireland

Yes I think the mike if one of the ones pointed to by Jan, but one is supposed to have two mikes in a headset, one pointing at your mouth and the other pointing outwards (actually it is implemented in a single mike unit normally AFAIK) so you get cancellation of ambient noise.

The single mike in this headset "should" never work in a noisy environment.

Administrator
Shoreham EGKA, United Kingdom

To be frank, I am surprised that this one only offers passive noise cancellation. If once it is decided to use electret technology, the added cost of a second cell and a differential amp should be negligible in the total price. It shows to me that the maker tried their very best to keep the price low.

EBZH Kiewit, Belgium

Yes, though I don't think the passive headsets use any electronics.

They would have no means to power it.

The normal 2 jack connection is just one jack for the headset speakers, and one jack for the mike which (never looked into it) is probably an electret mike whose bias voltage comes from the aircraft radio/intercom/whatever.

ANR headsets which always have power have the option of doing clever stuff in the mike, but I still don't think they do. I would bet even a Bose A20 just brings the mike straight out on the cable. One could test this by speaking into it with the batteries removed and the PTT button pressed...

ANR doesn't use the mike you speak into. It has a mike in each headset earcup, which is wired with an op-amp in antiphase, so that with no incoming audio there is zero sound pressure in the earcup. Any incoming audio is injected into this feedback loop so it doesn't get cancelled out as well. The process fails to work at higher frequencies, due to problems with sound waves having multiple paths inside the earcup, but it works well enough. The in-ear headsets can do superb ANR, but most of them don't need to.

Administrator
Shoreham EGKA, United Kingdom

Doesn't the microphone plug/jack always carry 12V dc power, for compatibility with the old carbon microphones? Think I remember some very clever fidgeting with that by most respected Mr. Jim Weir of California, USA.

The available power would be very limited, though.

EBZH Kiewit, Belgium

Luckily a lot of maintenance manuals have escaped into the wild and a google finds e.g. the one for the KX165A here.

Of course I had that one already in my collection but I can't post the URL for that

Page 208 shows what looks like a mike input, and +9V is available, via about 600 ohms, so you could draw a few mA from it. I hope I found the right bit....

Apart from that, the manual is a fascinating insight into what happens if you employ an electronics engineer whose salary does not reduce if he designs something that uses up 50% of the world's output of electronic components.

At every stage, if something could be done with 5 components, they use 50

Administrator
Shoreham EGKA, United Kingdom

Thanks guys!

Am I to understand from Peter's initial comments that simply replacing the mic is unlikely to solve the problem? Or is Peter suggesting that I should replace it, but with a different type of mic?

If a different type of one is it simply a case of choosing a different one and just soldering it in, or is using a different one a complicated job as other elements need to be changed too?

Sorry for the basic questions. This stuff is way outside my areas of knowledge.

Thanks Colm

EIWT Weston, Ireland

IMHO, to make a workable aviation headset you need a noise cancelling mike.

I found this.

The last link there (the PDF) shows how to do it.

There are various ready made ones e.g. this.

Administrator
Shoreham EGKA, United Kingdom

Never having used or owned headsets with active noise cancelling, I am - again - blessed by my ignorance. More relevant, O/P knew there was no ANR yet decided to buy it.

That said: my suggestion would be to replace the electret cell with a different type, which is why I illustrated some candidates. IME they all use the same technology so will all have comparable electrical parameters. However you could, before soldering the old one out, measure DC voltage across it, and compare that to the new one(s) after installation - if the value is more than 30% off, some further consideration might be in order.

I think the main difficulty will be to locate such an electret cell of acceptable dimensions, i.e. the same or smaller. Once that found, installing it in place should be a quick job.

EBZH Kiewit, Belgium
13 Posts
Sign in to add your message

Back to Top