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
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