[ELECRAFT] {OT} Transformer to change mic impedance

[DaveL G3TJP]

Hi all.  Has anyone any knowledge of a sub-miniature transformer to change the impedance of a 100k dynamic mic to 600 ohms?

I have a surfeit of old Shure mics and just about all are very high impedance.  Ideally, I'd like a transformer that could be tucked away in a spare corner of a hand-held PTT mic.

Thanks in advance.

Dave, G3TJP
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[Dale Parfitt-3]

Heil sells such a transformer- I have one here I used on an EV mic.

Dale W4OP

----- Original Message -----
From: "David Lankshear" <[hidden email]>
To: <[hidden email]>
Sent: Friday, February 25, 2011 12:43 PM
Subject: [Elecraft] [ELECRAFT] {OT} Transformer to change mic impedance

> Hi all.  Has anyone any knowledge of a sub-miniature transformer to change
> the impedance of a 100k dynamic mic to 600 ohms?
>
> I have a surfeit of old Shure mics and just about all are very high
> impedance.  Ideally, I'd like a transformer that could be tucked away in a
> spare corner of a hand-held PTT mic.
>
> Thanks in advance.
>
> Dave, G3TJP
> ______________________________________________________________
> 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 2/25/2011 9:43 AM, David Lankshear wrote:
> Has anyone any knowledge of a sub-miniature transformer to change the impedance of a 100k dynamic mic to 600 ohms?

Try it without the transformer before you decide that you need one. It
is VERY likely that it will work just fine. Use TXEQ to adjust for any
needed changes to frequency response, set the mic gain as needed.

73, Jim K9YC (audio guy)
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[Joe Subich, W4TV-4]

An alternative is the FET follower that Paul, W9AC documented
for the D-104.  While the 50 to 100K dynamic elements aren't
quite as high impedance as the D-104, the FET follower should
still do a good job and a singe J201 or MPF-102 might be less
expensive than a transformer, easier to find and certainly less
sensitive to magnetic fields <G>.

See: http://72.52.250.47/images/D104.jpg

73,

    ... Joe, W4TV


On 2/25/2011 9:42 PM, Jim Brown wrote:

> On 2/25/2011 9:43 AM, David Lankshear wrote:
>> Has anyone any knowledge of a sub-miniature transformer to change
>> the impedance of a 100k dynamic mic to 600 ohms?
>
> Try it without the transformer before you decide that you need one.
> It is VERY likely that it will work just fine. Use TXEQ to adjust for
> any needed changes to frequency response, set the mic gain as
> needed.
>
> 73, Jim K9YC (audio guy)
> ______________________________________________________________
> 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 2/25/2011 7:51 PM, Joe Subich, W4TV wrote:
> An alternative is the FET follower that Paul, W9AC documented
> for the D-104.

Another suggestion I had forgotten about. The original post said it was
a Shure mic. Many (most?) high impedance mics made by main line
companies like Shure and EV had built-in transformers with taps that
could be wired for Hi-Z or Lo-Z.  It's worth looking to see if that is
the case for your mic.

I have data sheets for many old Shure and EV mics, so if you post a
model number I'll try to look it up.

BUT -- I repeat my earlier advice -- hook it up, adjust the gain, listen
to it, and try correcting any frequency response shortcomings with EQ.  
It is VERY likely that it will work just fine.

73, Jim Brown K9YC
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