K2 and K3 Microphone Input Impedance

[John Huggins, kx4o]

Wayne et al.

I am surveying various rigs to see what their microphone input impedance
values might be.

I note the K3 schematics show just about every audio path including the
microphone's path terminated in 10k ohms or so.

In the KSB2 I see 1k ohm (or 180 ohms if /ATTEN is asserted).

Was there a compelling reason for having different termination values, 10k
vs. 1k, between transceiver model lines?

Thanks.

John


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[George & Jan]

John,
I would not select a radio on the input impedance of the microphone input!
It is not critical at all - should be at least 10 times the microphone
impedance.

Pro-Audio from as far back as the antique Western Electric unbalanced
systems of the 40s tend to be in the range of 1 k to 10 k. Mostly depends on
what the designer wants to emphasize. Lower would tend to reduce noise
pick-up. Higher would tend to load the mic less thus improving S/N. Probably
neither value is significant.

George
AI4VZ

-----Original Message-----
Was there a compelling reason for having different termination values, 10k
vs. 1k, between transceiver model lines?

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[John Huggins, kx4o]

Rest assured George, the mic input Z is not a rig selection criteria for
me.  This is for a completely different item I am developing to adapt my
mics to various rigs including the K2 and K3.

John

On 1/6/2011 5:55 PM, George & Jan wrote:

> John,
> I would not select a radio on the input impedance of the microphone input!
> It is not critical at all - should be at least 10 times the microphone
> impedance.
>
> Pro-Audio from as far back as the antique Western Electric unbalanced
> systems of the 40s tend to be in the range of 1 k to 10 k. Mostly depends on
> what the designer wants to emphasize. Lower would tend to reduce noise
> pick-up. Higher would tend to load the mic less thus improving S/N. Probably
> neither value is significant.
>
> George
> AI4VZ
>
> -----Original Message-----
> Was there a compelling reason for having different termination values, 10k
> vs. 1k, between transceiver model lines?
>
> ______________________________________________________________
> 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
>

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[Jim Brown-10]

On 1/6/2011 2:55 PM, George & Jan wrote:
> It is not critical at all - should be at least 10 times the microphone
> impedance.

Actually, the current applicable IEC Standard DEFINES the impedance of a
microphone as 5X its rated load impedance. And yes, a higher input Z is
better -- the rated impedance is a minimum value.  Most professional
mics have an impedance of 150-250 ohms, and most pro mic inputs have an
input impedance of at least 1K-1.5K ohms, and there are excellent
technical reasons for values of 5K ohms or greater.

73, Jim Brown K9YC
Member, AES Standards Committee and WG on Microphones
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