[Elecraft] Balanced Mic to Unbalanced Connection Follow Up Question

[Joe Subich, W4TV]

On 2020-06-09 8:14 PM, Don Wilhelm wrote:
> So --- make an adapter so that pins 2 and 3 are connected to the tip
> and ring of the mic jack,
No, no, no!  The ring of the K3/K3S rear panel mic jack *IS FLOATING*.
Pins 2 and 3 of the XLR *MUST BE* connected to tip and *SLEEVE*.

73,

    ... Joe, W4TV


On 2020-06-09 8:14 PM, Don Wilhelm wrote:
> 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.