"ian field" wrote in message
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"w9gb" wrote in message
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"ian field" wrote in message
news

"Michael A. Terrell" wrote in message
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default wrote:

On Sat, 16 Dec 2006 19:57:54 GMT, "ian field"
wrote:


"default" wrote in message


Try it with no battery installed. There is usually just an FET and
pull up resistor in it. Removing the battery should leave just the
FET and you'd have the pull up resistor/voltage source inside the
flash recorder - the way standard un powered electrets work.

Doubtful - the output of the OP's powered mic appears to be capacitor
coupled, so there's no DC path to supply the FET.

Well, cap coupled wouldn't work. I'd try it, nothing to lose, and
wouldn't you feel stupid if you didn't try that first?


No, since I don't expect it to work like that when its designed
properly. Also, you are applying a reverse voltage to the coupling
capacitor if you try this.


Since you mention that, if the cap is a tantalum even a small reverse
voltage can cause S/C failure - so it could work after all!!

That is why a non-polar tantalum is used in this application.



Didn't know such things exist! - got a pdf?

GOOGLE is your Friend for Internet look-ups !

Non polar tantalum capacitor - US Patent 5777840
http://www.patentstorm.us/patents/57...scription.html

Data sheets
http://www.digchip.com/datasheets/pa...parts_st41.php

Vishay
http://www.datasheetcatalog.com/data...f/T/C/TC.shtml

Kemet FAQ
http://www.kemet.com/kemet/web/homep...itor+Selection

You can read it straight from Bob Heil (and yes he installs and sells these
with this products)
A non-polar electrolytic, if available, could also be used.

IF you use other microphone elements (copper wound, magnetic
bobbin, dynamic) -- on a "phantom powered" device ---
then the DC power must be de-coupled.
You use a capacitor to block this DC power.
A 1 mFd. non-polar tantalum capacitor in series with microphone lead. You
may get by with a .68 or a .47 mFd but anything less (.01, .005 etc) will
not pass any speech audio worth
listening to). The cap MUST be a non-polar. This will keep the D.C. from
getting across the dynamic element while passing the speech audio through
the cap into the mic preamp circuitry.
http://www.heilsound.com/amateur/harmonics.htm#DC