[Elecraft] K3 low PEP Power on SSB

[Paul Christensen]

> This is getting more and more confusing. What exactly is the compatibility
> issue with the K3 and an electret microphone wired for Kenwood? I have a
> Heil Proset with the IC element (which is electret).

Knut,

The answer is going to become a bit more complicated until it becomes easier 
to understand the issue.  Here goes:

First, from the K3 operating manual, page 13:

"Bias must be turned on for the MH2, MD2, and Proset-K2. It must be off for 
Heil mics using the HC4 or HC5 elements."

We're really discussing two means of mic bias here.  One form of bias 
appears on Pin 1 (mic lead) on the K3's mic connector, while the other 
appears on Pin 6 (+8 VDC). The K3 has the ability (through a menu command) 
to self-bias an electret condenser through the mic lead on Pin 1.  When bias 
is activated through the K3's menu, the mic lead is clamped with a + 4.5 V 
DC bias voltage for electrets.   The + 8 VDC on Pin 6 is always on; it never 
turns off through the menu command.

However, other forms of electrets and mic buffer circuits are not biased 
through the mic lead.  For example, I am using a highly-modified D-104 with 
an ultra Hi-Z FET input as a voltage-follower.  In the particular circuit I 
am using, I cannot bias the mic lead directly like you can with your Heil 
Proset.  Instead, I must take +8 VDC from Pin 6 and apply it to the FET.  In 
a nutshell, the K3 can produce mic bias either by clamping the mic lead at 
pin 1 with +4.5 VDC when activated in the menu OR mic bias can be obtained 
through Pin 6 on the K3 mic connector.

What we've been discussing here is that Kenwood places + 8 VDC on Pin 5, 
while Elecraft is using Pin 6 for the same purpose.  That's primarily where 
the confusion lies.

The bottom line is that if you're using a Heil Proset, you should simply 
activate bias through the K3 menu and forget about Pin 6.  I just took the 
soldering pencil to my D-104's connector and moved the power lead from Pin 5 
to Pin 6 and all is well now.  No surprise, now that I see what's really 
going on -- and I was able to use the low-gain mic setting.  I'm a happy 
camper now.

Finally, Elecraft has given us the choice to bias either way, but because of 
the foregoing reasons, the Kenwood pin-out is certainly not 100% compatible 
with the K3.

Paul, W9AC