[Elecraft] K3 microphone input noise

[g0afh]

Hi,

My K3 last arrived last week and I have been getting to grips with it. 
However, I think I may have an issue with noise in the mic amp /adc.

The headset I hoped to use is one that I have successfully used with my 
FT1000MP, a Sennheiser HMD25-1. This has a 200 ohm dynamic mic insert. 
With the K3 I find that I need to use the high gain setting and a 
relatively high mic gain level (30 -40) to get anywhere near the 
required 4-5 bars of ALC. With that much gain I hear more noise than I 
would expect to. The noise is mostly white but has a distinct whine 
which I estimate to be at around 1500Hz. The situation is the same using 
the front or rear mic sockets.

I have also tried a number of other headsets. A Bayer DT190  with a 200 
ohm dynamic mic insert gives similar results to the HMD25-1. A 
Sennheiser HME25-1 which has an electret mic insert is a little better 
(probably because it has a higher output level) although still requires 
fairly high gain.

The best results so far have been with a low cost computer headset or a 
£1.00 electret mic capsule. With both of these I was able to use the low 
gain setting and a mic gain less than 20.

So, some questions...

What sort of gain level should I expect to use for a dynamic mic?

Are other K3 mic amps as noisy as the one I have, if not then where 
should I start looking for the noise issues?

Does anyone else hear the tone in the noise with the mic gain turned up?

73
Ian.