Yes, I had realised my confusion, too. Apologies!
The link I posted is very very slow. It appears to be a home server on ADSL and using dyndns to get the public IP.
But yes you are right. A noise cancelling mike is used on all aviation headsets - it has to be. ANR is a different system used to cancel noise entering the ears.
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
I think you and Peter are talking at cross purposes when it comes to noise cancelling.
I think you are talking about what's known as Active Noise Reduction or Electronic Noise Cancelling and refers to the speaker part of the headset. It attempts to reduce the ambient noise inside the ear cup by creating an inverse sound wave.
I think what Peter is talking about a noise cancelling microphone which attempts to remove background noise from what the microphone detects.
Peter's link doesn't work but if it's how to make a mic then unfortunately I imagine that it's way beyond what I'm capable of.
The ready made one would be perfect, but unfortunately I can't see any way of attaching it to the boom. So I think I'll give Jan's suggestions a try and see if they can make a satisfactory solution.
Thanks for the advice guys!
Colm
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.
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
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
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.
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.
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.
