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K3/K3S Pin 1 question

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K3/K3S Pin 1 question

I am building a switchbox to allow use of a Heil PR-781 microphone to be
used by my K3S and K3, the switchbox using XLR connectors. I note that
in the Heil XLR cable ended in an 8-Pin Foster has mic low (-) tied to
ground and (+) tied to mic high.

Knowing that the XLR pin 1 should be chassis ground, my question is, "At
the switchbox, should I tie XLR pins 1 and 2 together and only switch
XLR pin 3 between radios?" IOW, should XLR pins 1 and 2 be chassis
grounded or should I chassis ground pin 1 and switch both XLR pins 2 and 3?

Thanks in advance.

73,
Dan

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Don Wilhelm-4

Re: K3/K3S Pin 1 question

Dan,

Jim Brown K9YC or Joe W4TV would be a better resource than I am, but if
it were mine, I would preserve the balanced configuration through your
switchbox and only connect the mic low to ground at each radio's plug.

73,
Don W3FPR

On 9/14/2015 1:12 PM, Dan Atchison via Elecraft wrote:

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Bob McGraw - K4TAX

Re: K3/K3S Pin 1 question

In reply to this post by Elecraft mailing list

Maintain the signal path integrity all the way through the switching
arrangement. That means 3 poles to switch from the XLR input to the 8
pin Foster connectors. Keep all away from chassis ground. If you
believe the box should be grounded, I suggest doing so at the input XLR
pin #1 to chassis ground. And keep ground between the outputs, being
the Foster connectors, separate so as not to connect the two radios
together through the shield/ground.

73
Bob, K4TAX
K3S s/n 10,163

On 9/14/2015 12:12 PM, Dan Atchison via Elecraft wrote:

> I am building a switchbox to allow use of a Heil PR-781 microphone to
> be used by my K3S and K3, the switchbox using XLR connectors. I note
> that in the Heil XLR cable ended in an 8-Pin Foster has mic low (-)
> tied to ground and (+) tied to mic high.
>
> Knowing that the XLR pin 1 should be chassis ground, my question is,
> "At the switchbox, should I tie XLR pins 1 and 2 together and only
> switch XLR pin 3 between radios?" IOW, should XLR pins 1 and 2 be
> chassis grounded or should I chassis ground pin 1 and switch both XLR
> pins 2 and 3?
>
> Thanks in advance.
>
> 73,
> Dan
>
> ______________________________________________________________
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>
>

Jim Brown-10

Re: K3/K3S Pin 1 question

In reply to this post by Elecraft mailing list

On Mon,9/14/2015 10:12 AM, Dan Atchison via Elecraft wrote:

The answer is that it depends on the kind of cable used -- single
conductor plus shield with mic low on the shield, or twisted pair plus
shield, with the mic low not connected to the shield.

If twisted pair plus shield, carry mic high and mic low to their
designated pins on rig, and connect the cable shield to the shielding
enclosure (the chassis, in a K3 or K3S). For any shielded twisted pair
going to an unbalanced input, the connection between one side of the
audio and the chassis should be at the radio input. This allows audio to
stay on the twisted pair, which inherently rejects noise by virtue of
its twisting.

If a single conductor plus shield, connect mic high in the cable to mic
high in the radio, and the cable shield to the chassis. In your plan,
you would want to switch everything but the shields.

NEVER connect a cable shield to a return pin unless that pin has a
direct short to the chassis at the connector. To do so is, by
definition, a Pin One Problem, and a major cause of hum, buzz, and RFI.

73, Jim K9YC

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Jim Brown-10

Re: K3/K3S Pin 1 question

In reply to this post by Don Wilhelm-4

On Mon,9/14/2015 10:25 AM, Don Wilhelm wrote:
> I would preserve the balanced configuration through your switchbox and
> only connect the mic low to ground at each radio's plug.

As usual, we agree. :)

73, Jim K9YC
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Joe Subich, W4TV-4

Re: K3/K3S Pin 1 question

In reply to this post by Don Wilhelm-4

On 9/14/2015 1:25 PM, Don Wilhelm wrote:
> if it were mine, I would preserve the balanced configuration through
> your switchbox and only connect the mic low to ground at each radio's
> plug.

*Absolutely* ... connect the *shield* of the XLR cable to chassis and
switch both mic + and mic - carrying both wires all the way through to
the transceiver. At the transceiver the shield should be connected to
the *shell* of the Foster plug which should, in turn, be bonded to the
*case/chassis* of the transceiver.

Connecting a shield via a connector pin to a circuit board then via a
"long" trace back to the chassis/case (power supply return), is the
very definition of the "pin 1 problem." Every amateur transceiver has
a pin 1 problem and most third party accessories have to deal with that
issue in their own (typically non-standard) way.

73,

... Joe, W4TV

On 9/14/2015 1:25 PM, Don Wilhelm wrote:

> Dan,
>
> Jim Brown K9YC or Joe W4TV would be a better resource than I am, but if
> it were mine, I would preserve the balanced configuration through your
> switchbox and only connect the mic low to ground at each radio's plug.
>
> 73,
> Don W3FPR
>
> On 9/14/2015 1:12 PM, Dan Atchison via Elecraft wrote:
>> I am building a switchbox to allow use of a Heil PR-781 microphone to
>> be used by my K3S and K3, the switchbox using XLR connectors. I note
>> that in the Heil XLR cable ended in an 8-Pin Foster has mic low (-)
>> tied to ground and (+) tied to mic high.
>>
>> Knowing that the XLR pin 1 should be chassis ground, my question is,
>> "At the switchbox, should I tie XLR pins 1 and 2 together and only
>> switch XLR pin 3 between radios?" IOW, should XLR pins 1 and 2 be
>> chassis grounded or should I chassis ground pin 1 and switch both XLR
>> pins 2 and 3?
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

bdenley

Re: K3/K3S Pin 1 question

In reply to this post by Jim Brown-10

I agree with Don as well here. I use a Behringer Shark DSP110 which has both balanced XLR and 1/4 inch mono inputs and outputs that can be set to line or mic levels. It also provides a noise gate and mic gain if you need it. You can stay balanced as far as you want. It was ~$50 used.
Brian
KB1VBF
Sent from my iPad

> On Sep 14, 2015, at 5:52 PM, Jim Brown <[hidden email]> wrote:
>
>> On Mon,9/14/2015 10:25 AM, Don Wilhelm wrote:
>> I would preserve the balanced configuration through your switchbox and only connect the mic low to ground at each radio's plug.
>
> As usual, we agree. :)
>
> 73, Jim K9YC
> ______________________________________________________________
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