I'm trying to get a 500R impedance dynamic mic working with an old
IC-730. The rig does not have a built in preamp so you have to have
one in the mic casing.
I've found a suitable design by G3SEK (http://www.ifwtech.co.uk/g3sek/
in-prac/best-of.htm#icom) but it seems to be designed for Heil HC4 or
HC5 inserts. These seem to be 1000 ohm impedance. Am I going to cause
problems by using a 500 ohm mic with a preamp designed for 1000 ohms?
Can the deisgn of the preamp be modified for 500?

Cheers
Tom 2E0WNT

Tom Corker wrote:
I'm trying to get a 500R impedance dynamic mic working with an old
IC-730. The rig does not have a built in preamp so you have to have
one in the mic casing.
I've found a suitable design by G3SEK (http://www.ifwtech.co.uk/g3sek/
in-prac/best-of.htm#icom) but it seems to be designed for Heil HC4 or
HC5 inserts. These seem to be 1000 ohm impedance. Am I going to cause
problems by using a 500 ohm mic with a preamp designed for 1000 ohms?
Can the deisgn of the preamp be modified for 500?

Cheers
Tom 2E0WNT



The 1,000 ohm input impedance shouldn't cause any problems at all;
many microphone preamplifiers have input Zs higher than the nominal
figure for the microphones with which they're used.

With all good wishes,

Kevin, WB4AIO.

Tom Corker wrote:
I'm trying to get a 500R impedance dynamic mic working with an old
IC-730. The rig does not have a built in preamp so you have to have
one in the mic casing.
I've found a suitable design by G3SEK (http://www.ifwtech.co.uk/g3sek/
in-prac/best-of.htm#icom) but it seems to be designed for Heil HC4 or
HC5 inserts. These seem to be 1000 ohm impedance. Am I going to cause
problems by using a 500 ohm mic with a preamp designed for 1000 ohms?
Can the deisgn of the preamp be modified for 500?

Cheers
Tom 2E0WNT

No need - that design will be fine as it stands.


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

On Tue, 08 Dec 2009 06:20:05 -0800, Tom Corker wrote:

I'm trying to get a 500R impedance dynamic mic working with an old
IC-730. The rig does not have a built in preamp so you have to have one
in the mic casing.
I've found a suitable design by G3SEK (http://www.ifwtech.co.uk/g3sek/
in-prac/best-of.htm#icom) but it seems to be designed for Heil HC4 or
HC5 inserts. These seem to be 1000 ohm impedance. Am I going to cause
problems by using a 500 ohm mic with a preamp designed for 1000 ohms?
Can the deisgn of the preamp be modified for 500?

The 'ideal' mic preamp would have an infinite input impedance, so you
should be fine from that standpoint. If the voltage levels are
significantly different you'll have a problem -- but for that you just
need to try it and find out.



--
www.wescottdesign.com