[ARC5] Driving the BC-456

[J Mcvey]

I was noodling with the electret mike circuit today.It turns out that the initial reverse engineering results were pretty close.The input Z is very low, in the 30-50 ohm range. 4Vpp DOES NOT overdrive the modulator!This falls in the T-17 mike spec which was a max of 1.7 Vrms ( 4Vpp = 1.41Vrms)
It looks to be about 80% modulation@ 4Vpp. 
I thought that would be enough , but it looks like it would be good to have more adjustable range to5Vpp or 6Vpp.
The internal tone modulation looks like 100%+
So far, the circuit consists of two active devices. A LM3900 and MPSA06 npn transistor.A LT1006 or equivalent would probably work as well-maybe better, but I have the LM3900's on hand.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/arc5/attachments/20170326/6a2d17ec/attachment.html>