[Elecraft] Pin 1 Problem?

[Jim Brown]

On Fri, 2 Jan 2004 11:34:21 -0000, Ralph McClintock wrote:

>After awhile I realized that the mic connector on the K2 is soldered to the front
>panel board and not mounted to the front panel itself so the shell never sees
>ground. 

You have just described a classic design error known in the pro audio
world as a "pin 1 problem" (so named because the shield of the XLR
connector commonly used in pro audio is connected to pin 1). The shield
of the mic cable SHOULD go straight to the chassis. If current flowing
on the shield has to find ground via the circuit board, the voltage
drop across any stray inductance in the path can easily find it's way
into the signal path on the circuit board. 

Pin 1 problems are a major cause of RF interference. If there is any RF
in the shack (common with any long wire antenna), the shield of the mic
cable can act like an antenna. I would expect this to cause a problem
when the mic input of a K2/100 is driven by a computer's sound card. 

Wayne -- if Ralph is right, this needs immediate attention!  

BTW, the same considerations also apply to all other inputs and
outputs. 

Jim Brown
Audio Systems Group, Inc.
Chicago
http://www.audiosystemsgroup.com