[Elecraft] MH2 question

[Don Wilhelm]

Ed,

Several responses to your post have brought comments regarding the K3 TX 
audio, but I have not seen any specifically addressing the K2.
The K3 TX audio can be tailored using the 8 band TX Equalizer which can 
be used to make most any microphone sound like the best studio 
microphone in the world if you are inclined to do a bit of tailoring - 
no need for an external equalizer, it is built in.

If you have a K2, you may be interested in the following - If not, you 
may want to hit the delete key now, the rest is K2 related.

I do not think Gary has aligned many K2s in the past few years.  I have 
handled most of the more recent Elecraft K2 repairs, and do not see your 
call in my records, so I am wondering just how long ago that alignment 
was performed.

You may want to look at your K2 rather than the microphone.  I would 
hate to see you spend $50 or so on a mod to your microphone and find no 
added benefit because of limitations in your K2 or your SSBA and SSBC 
menu settings.  K2s that I have aligned often garner unsolicited TX 
audio reports, and I have received that report from many customers.  The 
MH2 does have the peaking response in the 2800 to 3200 Hz region - the 
same as many other ham microphones.

How old is your K2, and what is the width of the KSB2 filter (2.1kHz or 
2.4kHz)?  The early KSB2 boards had the 2.1kHz filter while later ones 
have the 2.4kHz filter - that filter is used on transmit as well as 
receive.  To determine which one you have, look at the capacitor row 
just to the left of the crystals on the KSB2 board - if all 6 capacitor 
locations are populated, you have the earlier 2.1 kHz filter, but if 
there are only 4 capacitors fitted, it is the 2.4 kHz filter.  Should 
you want to change the filter width, Elecraft has the SSBCAPKT available 
to do that - but check the crystals first.  If they are labeled anything 
other than 49136-S, you must replace the crystals when widening the KSB2 
filter.  If your KSB2 has the older crystals, your base K2 RF board 
likely has the older crystals as well and will result in better filters 
if replaced. Elecraft has a set of 7 matched crystals as well as a 
matched set of 14 available.

The other thing that will affect your SSB transmit (and receive) audio 
is the placement of the audio passband for LSB and USB.  That may be 
corrected by proper filter alignment (CAL FIL).

There is another thing that can affect the K2 TX audio, and that is too 
much bass.  The KSB2 does allow low bass frequencies to be transmitted.  
While some hams like that, it uses excessive power in the PEP envelope.  
You can reduce that response by changing 2 capacitors on the KSB2 
board.  Change C34 to a 0.47uF electrolytic and change C32 to a 
capacitor between 0.0033 and 0.005 uF. (4700pF is an easily available 
mid-range value).

73,
Don W3FPR

On 7/9/2015 11:06 AM, Eddy Avila wrote:
> Has anyone sent their Heil MH2 to AB5N Bob Nagy for his upgrade? I've never been impressed with my K2 SSB tx audio and I've done everything Elecraft has recommended to improve the TX audio, including sending it to Gary for alignment -- Gary did a wonderful job aligning my K2, but the K2 TX audio still leaves a lot to be desired!!
> Thanks for any advice you can offer regardnig the AB5N mods.
> 73
> ed 		 	   		
>