[Elecraft] Balanced Mic to Unbalanced Connection Follow Up Question

[Don Wilhelm]

So --- make an adapter so that pins 2 and 3 are connected to the tip and 
ring of the mic jack, then add a one wire 'dongle' exiting from the XLR 
plug that is connected to XLR pin 1.  Connect that wire to a screw on 
the chassis of the K3/K3S/KX2/KX3.

Noise, hum and buzz are  then conducted from the shield onto the 
"outside" of the radio enclosure where it should be - avoiding the "pin 
1" problem that K9YC often refers to.

For those not familiar with the "pin 1" problem, it is caused by the 
jacks in the transceiver (or other gear) being connected to the circuit 
board ground plane where it can couple into sensitive circuits and cause 
coupling problems.  Proper bonding between enclosures following the path 
of audio or coax lines can minimize that problem by keeping some of the 
noise, hum and buzz mostly on the outside of the enclosure rather than 
injecting it into the circuits on the board ground plane.
We did not have this problem when we mounted the jacks on the enclosure 
rather than mounting them on the boards, usually isolated from the 
outside of the enclosure.

73,
Don W3FPR

On 6/9/2020 7:47 PM, Joe Subich, W4TV wrote:
> 
> Correcting *ALL* the typos <G> ....
> 
> 
>> So which is correct?
> 
> They are electrically equivalent.
> 
> Pin 2 of the XLR connection is Mic+
> Pin 3 of the XLR connection is Mic-
> Pin 1 of the XLR connection is the cable shield (ground).
> 
> Mic audio is present between pins 2 and 3.
> 
> Pin 1 is nothing more than a shield and should be independently
> connected to the *chassis at the jack*.
> 
> Good quality XLR cables use a *TWISTED PAIR* for pins 2 and 3.
> That twisted pair is shelf shielding - particularly good for
> rejecting hum. Connecting a shield in parallel with the wire
> for pin 3 "unbalances" the twisted pair and makes it much
> more susceptible to hum and RFI - particularly when the shell
> of the 3.5mm plug/jack is not tied to the chassis/case of the
> transceiver.