[Elecraft] K3 Hum on Audio...

[Jim Brown]

On 2/3/2012 9:25 PM, Guy Olinger K2AV wrote:
>    There is that mu-metal stuff. But mostly
> that level of induction from something pulling that much current into
> microphone level devices is a really really hard cure, hence
> "uncurable" in quotes.

 From the symptoms, it was coming into the LINE INPUT -- he said the 
Line Input was cranked up and he turned it down or off and cured the 
problem.

Yes, mu-metal shielding cures the problem, but that's a lot more 
expensive than what's in the radio.  The real issue is that transformers 
are the wrong solution. All that is needed is simple chassis-to-chassis 
bonding between the equipment being interconnected. This sort of design 
error is  what happens when you assign digital guys to design audio 
circuits.  :)

73, Jim Brown K9YC