[Milsurplus] SIMPLE Carbon Microphone Substitute.

[Hubert Miller]

" Since the JFET channel is a single, uninterrupted piece of semiconductor
material, there is usually no difference between the source and drain
terminals."
Also, doing some brief message board look-ups, i noticed some people had
reported their electret worked both ways, either polarity. I did not see yet
a 
message  boards post explaining that, so to  me at least, it remains a
puzzlement, i mean the reported electret polarity dependence. Some did
mention the
worth of having the electret case to ground, for shielding. 
It occurred to me the that the DC resistance of the electret element, tho in
megohms, might be operative here. 
-Hue 

-----Original Message-----
From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of
AKLDGUY .
Sent: Sunday, May 29, 2016 2:50 PM
To: milsurplus <milsurplus at mailman.qth.net>
Subject: Re: [Milsurplus] SIMPLE Carbon Microphone Substitute.

> https://en.wikipedia.org/wiki/Electret_microphone#/media/File:Electret
> _conde
 nser_microphone_schematic.png
>
> It's a two terminal variable resistance.
> I hadn't realized this feature of the many electrets i've harvested.
> What will remain a puzzlement for me, is why, as Dave reported, his 
> electret is entirely polarity dependent.
> The FET should be able to be polarity "rolled", and the electret 
> element is permanently polarized, a DC nonconducting device.

It shouldn't be a puzzlement. FET's are polarity conscious, confirmed by
David's finding that the circuit worked with the polarity one way only.

His configuration of the FET as a source follower is actually rather good,
with the FET drain-source current turning on the transistor and the low
impedance output as a source follower driving the base. Probably explains
why the audio quality is good. I intend to use this circuit in my BC-AO-230.

73 de Neil ZL1ANM