[Elecraft] K2 and Heil Mics...

[Kevin Cozens]

At 02:30 PM 05/27/2002 -0400, you wrote:
>I'm interested in any experience in using a Heil mic (any style)
>containing either the HC-4 or HC-5 dynamic element with a K2.  I
>understand these mics apparently have a lower output than the
>Heil/Elecraft condenser MH-2 mic, but wondered what success and/or
>modifications have been done to make the HC-4/5 work directly on the K2.
>
>BTW, which wiring scheme is used?  Kenwood, Yaesu....?

I have a Heil BM-10 headset with the HC-5 element. In order to use it with 
the K2, I have made the changes to the KSB2 as suggested on this list. 
Namely, changing R14 from 1K to 10K, and R2 from 5k6 to 1k. R15 should also 
be changed if you ever plan on using the SSbA level of 1 (10db cut). With 
the current value of 180 ohms, you would never be able to get the VOX to 
trip if you set SSbA to 1.

The above change helps and the audio as heard on a separate receiver seems 
ok. I haven't fully tested this myself in on-air QSOs as the band 
conditions have been lousy lately. I haven't been able to get in touch with 
some of the net controllers who know my voice from the other rig I used to 
use to do any comparison.

With the change of R14, the audio level going in to U3-4 goes from about 
.2mV to about 2mV as best as I have been able to measure. Operating with 
VOX mode requires you talk more loudly than you might normally talk on 
other rigs in order to trip the VOX.

I rewired the BM-10 connector so I wouldn't have to change any jumpers in 
the K2.

I am not personally satisfied with the VOX performance even after the mods 
with my BM-10. Perhaps a future version of the KSB2 would have a variable 
mic gain circuit built-in as well as user configurable VOX sensitivity.

I think it might be possible to modify the KSB2 to improve VOX sensitivity. 
The VOX will trip if COMP OUT exceeds ALC THR. If the level of ALC THR is 
reduced via changes in the firmware it should increase VOX sensitivity 
although I don't know what effect it will have on the ALC operation.

Alternatively, a resistor divider at the output of U3-6 to reduce ALC THR 
could be done but again, it may affect ALC operation.

A third possibility I am considering trying is isolate pin U4-3 (cut the 
trace going to it near the pin) and add a resistor divider (or small trim 
pot) between U2-5 and ground with the center going to U4-3. In theory, 
using large value resistors (ie. >100k?) in the divider should have little 
to no impact on the ALC operation. I haven't tried it yet. If anyone else 
does, or cares to comment on the idea, I'd be interested to hear from them.


Cheers!

Kevin.  (http://www.interlog.com/~kcozens/)

Owner of Elecraft K2 #2172        |"What are we going to do today, Borg?"
E-mail:kcozens at interlog dot com|"Same thing we always do, Pinkutus:
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