View Full Version : Mic Gain Adjustment

4th Sep 2010, 17:36

I have a pair of Sennheiser HMEC-25KA's and although they're excellent I do pick up some hiss from my mic while on the 737 flight deck. I was wondering if anyone had managed to decrease the sensitivity of the mic by using the screws on the microphone itself. It's billed as an adjustable gain mic but I can't find any information regarding how to do it!


5th Sep 2010, 16:26
Anticlock to reduce gain, clockwise to increase via a small hole I believe just inboard of the mic inlet. Bring a mini flat head screwdriver (eyeglass size) with you to work and adjust as necessary. Took me a wee while to get it just right. Also, using a quality windscreen will help tremendously. Tried mine without and the plosive artifacts were not worth the increased sensitivity.

5th Sep 2010, 20:38
plosive artifacts ??

Nearly all mics are adjustable for gain, if one has the manual and knows what they are doing.
All too often, however...the gain is turned up too high, which often results in distortion for the receiving station.
Easy does it, with adjustments.
As I use a David Clark H10-30 headset in my private airplane, a very small clockwise adjustment was all that was needed.
The tower responded...'loud and very clear, what kind of radios are you using?
My response...'King Gold Crown, forty years old and still working to perfection'.

These comm sets (KTR9000 series) were installed in UAL B737's in 1969, and yes, they still work good.
Collins 618 series...likewise.
Yes, however, very reliable.
I have friends who have Garmin 430/530 sets, which include comm units. and these have proven rather unreliable, in extended service.
Great...you can navigate, but not communicate.