[Elecraft] Mic Gain, K2/100

[JIMMY D HARRIS]

Bill wrote,

"........on SSB, the voice peaks of the K2 are 25-30% lower than those of 
the FT-890. I am using dynamic mikes on both radios... on the K2 it's a 
Yaesu MH-31 Mic. I also used this mic on both radios and noted voice power 
peaks almost twice that of the K2 (70 w vs 40w). My K2 is set for SSBA of 3, 
and SSBC of 3-1. My KSB2 firmware is 1.07

I have seen a few references to mods on the KSB2, including swapping 
resistors to increase mic gain. I have also seen references that they should 
not be done on K2/100 units.

Are there any internal mic gain mods that can be used on the KSB2 in a 
K2/100? Is there anything else I can do short of the external mic amp?"


Bill
W1PA (K2 FT #61)

Bill and the group,

Earlier this year I researched the above and found some interesting 
information.  Per the response to my query to Support the mic audio input 
should be minus 27 db nominal plus or minus about 6-7 db.  They actually 
gave me a milivolt level that translates to the above numbers.  The "gold 
standard" in commercial broadcasting is minus 40 db for microphone input.  
Most dynamic and electret microphones available to amateur radio operators 
have an output of minus 40 to minus 60 db.  So the average microphone will 
produce about two to five "S" units less output from a K2 than it is capable 
of producing.  Many people report to get maximum usable audio they run both 
full mic gain and full or nearly full compression.  I've compared output 
levels from my K2/100 with my IC-746pro and found that both full mic gain 
and nearly full compression is needed with the K2/100 to get equal output.  
I was using an electret microphone with the K2/100 that had an advertised 
output of minus 38 db and a Heil Goldline (HC-5 - wide element) with the 
IC-746pro.  Many receive good audio reports with a variety of microphones 
but if you set up some simple bench tests you will find that many 
microphones without proper preamplification will not drive the K2/100 to 
it's capacity.

At one time Heil made at least two microphones for the K2 with a high output 
amplifier in their elements to provide the correct level for the K2.  At 
this time I think there is only a headset available with the high output.

When I purchased my K2/100 I also purchased an MD2 (Heil) microphone that 
had the correct output.  Somehow the element got damaged and needed 
replacement.  I could not get a replacement (long story) so I substituted a 
commercially available element and run full gain and almost full 
compression.  I've tryed a homebrew preamp and found it troublesome (noise, 
not variable).  My newest thought is to find an equalizer with a built in 
preamp.

This is one thing that Elecraft should address in their upcoming K3 or K2A. 
-;)

Jim, AB0UK
K2/100  SN 4787