Wiring the Shure 450 mic for K3

[Benson-2]

I see in the K3 manual that the mic connector has one pin for PTT and two grounds. My mic, a Shure 450 (http://www.shure.com/stellent/groups/public/@gms_gmi_web_ug/documents/web_resource/us_pro_450_series_2_ug.pdf) has a red and black wire for PTT. They are not part of the audio circuit but are just shorted by the PTT in the mic. Can anyone offer any guidance in wiring this mic?

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[Don Wilhelm-4]

Benson,

You can connect the black wire to either pin 7 or pin 8 and the red wire
to pin 2 and it will work with the K3.  Other amateur transceivers (some
Kenwoods) have the PTT  return separate from the AF return.  I believe
the PTT return is pin 8 and the AF Return is pin 7, so if you also want
it to operate with all Kenwood transceivers having the 8 pin connector,
wire the black wire to pin 8 and the shield plus the white wire pin 7 -
the green wire (AF) goes to pin 1.

73,
Don W3FPR

Benson wrote:
> I see in the K3 manual that the mic connector has one pin for PTT and
> two grounds. My mic, a Shure 450
> (http://www.shure.com/stellent/groups/public/@gms_gmi_web_ug/documents/web_resource/us_pro_450_series_2_ug.pdf)
> has a red and black wire for PTT. They are not part of the audio
> circuit but are just shorted by the PTT in the mic. Can anyone offer
> any guidance in wiring this mic?
>
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[Iain MacDonnell - N6ML]

Hmm, but there has been a recommendation to connect the mic return
and shield to the connector chassis, instead of using pin 7, to avoid
the "pin 1 problem".

http://n2.nabble.com/Microphone-ground-td1329465.html

     ~Iain



Don Wilhelm wrote:

> Benson,
>
> You can connect the black wire to either pin 7 or pin 8 and the red wire
> to pin 2 and it will work with the K3.  Other amateur transceivers (some
> Kenwoods) have the PTT  return separate from the AF return.  I believe
> the PTT return is pin 8 and the AF Return is pin 7, so if you also want
> it to operate with all Kenwood transceivers having the 8 pin connector,
> wire the black wire to pin 8 and the shield plus the white wire pin 7 -
> the green wire (AF) goes to pin 1.
>
> 73,
> Don W3FPR
>
> Benson wrote:
>> I see in the K3 manual that the mic connector has one pin for PTT and
>> two grounds. My mic, a Shure 450
>> (http://www.shure.com/stellent/groups/public/@gms_gmi_web_ug/documents/web_resource/us_pro_450_series_2_ug.pdf)
>> has a red and black wire for PTT. They are not part of the audio
>> circuit but are just shorted by the PTT in the mic. Can anyone offer
>> any guidance in wiring this mic?
>>
> _______________________________________________
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[Don Wilhelm-4]

Iain,

While that is true in many respects, the following facts are also true:

1) The K3 mic connector shell is grounded - so purists should connect
the shield wire from th emic element to the shell of the Foster plug.
2) The K3 original design used a 100 uHy inductor in the ground path
(pins 7 and 8) of the mic jack input.  That has been corrected in the
current build of K3.  Those who have earlier K3s should short out Front
Panel L4 as described in the Elecraft Application Note "Front Panel
Microphone Circuit Modification".
3) The above will be a benefit, but it still does not completely solve
the 'pin 1 problem' (although it comes as close as practical (see below).
4) To truly solve the 'pin 1 problem', the microphone jack shell should
be connected directly to the *enclosure* at the jack location (rather
than to the board ground) - that is difficult to achieve with the
enclosure mounted over a PC board.  It was not a problem in older
equipment where the jacks were fastened to the enclosure itself rather
than fastening to the PC board.

If some users have a need to do so, it would be possible to add a solder
lug on the inside of the Front Panel and connect it by a short path to
the microphone jack shell - that would be the proper "pin 1" solution.  
But since that would require a mounting hole (for the solder lug) in the
K3 Front Panel metalwork, I doubt that many owners would be willing to
do that.  There is space to mount a solder lug on the bottom flange of
the front panel metalwork, so some owners may be willing to add one
there (just below the mic jack) - the solder lug can be positioned in
such a way that it is possible reach into the left end and solder (and
desolder) it to the ground wire around the mic jack when the front panel
metalwork is installed (or removed).

After the change to bypass L4 is in place, mic jack pins 7 and 8 both
have a relatively short path to the board ground plane, and in all but
the most extreme situations, it will be sufficient.

73,
Don W3FPR

Iain MacDonnell - N6ML wrote:
>
> Hmm, but there has been a recommendation to connect the mic return
> and shield to the connector chassis, instead of using pin 7, to avoid
> the "pin 1 problem".
>
> http://n2.nabble.com/Microphone-ground-td1329465.html
>
>     ~Iain
>
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[Bill Steffey NY9H]

I thought those with concern or issues have already taken pin 7 & 8
to ground...
"bypassing" the  inductors and L7 on the rear mic input

bill

At 02:17 PM 12/19/2008, Iain MacDonnell - N6ML wrote:

>Hmm, but there has been a recommendation to connect the mic return
>and shield to the connector chassis, instead of using pin 7, to avoid
>the "pin 1 problem".
>
>http://n2.nabble.com/Microphone-ground-td1329465.html
>
>     ~Iain

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