[Elecraft] K3: 6M SSB audio hash

[Jim Brown]

On Fri, 6 Jun 2008 21:22:41 -0400, Joe Subich, W4TV wrote:

>There is a significant problem in using balanced input with any 
>"amateur mic" - including Icom, Kenwood, Yaesu and Heil.  Yaesu, 
>Kenwood and Heil connect the shield of the mic cable to the mic 
>return and not chassis (ground).  Icom uses the shield as the 
>mic return.  

>When the shield of the mic cable is tied to the low side of a 
>balanced input, RF that SHOULD go to ground/chassis is forced 
>through the mic preamp instead.   With the shield tied to the 
>mic return there is effectively a 10' piece of wire (antenna) 
>connected to the mic input unless the mic return is tied to 
>the chassis and the chassis is connected to a solid RF ground. 

This is not correct. There is nothing wrong with connecting an 
unbalanced mic to a balanced input -- you simply unbalance the 
input by grounding one side of the input. You lose the benefit of 
the balanced circuitry's ability to reject noise, but the input 
will work fine. The correct wiring is simply hot to one side, 
shield to the other side AND the chassis. 

I do have a serious quarrel with the W2IHY equalizer though -- it 
is FAR more complex and expensive than needed to get great audio 
from a pro mic with a ham rig. All you really need for an 
equalizer is a good quality capacitor of suitable value in series 
between the mic and the mic input of the radio. The capacitor is 
chosen to provide a low frequency rolloff fairly high in the 
audio passband. See

http://audiosystemsgroup.com/HamInterfacing.pdf

I have used a circuit like this with an EV RE16 and several rigs. 
Total cost about $0.50. It would work equally well with any good 
low-Z dynamic mic. I've also changed values in coupling 
capacitors in the K2 to achieve the same result, and that works 
quite well too. You don't need the capacitor with a K3, of course 
-- the equalizer in DSP does the job. 

Pro dynamic mics are easily connected to ham rigs -- since 
they're balanced, one side of the balanced output goes to the mic 
input, the other side goes to audio return, and the shield goes 
to the chassis. I've done this quite successfully with an Omni V, 
a TS850, and FT1000MP. By successfully, I mean that I get VERY 
competitve, clean, contest-quality audio that cuts through QRM 
and noise.