Author Topic: 2 Stage Preamp gate not closing  (Read 1233 times)

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Offline blewisjrTopic starter

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2 Stage Preamp gate not closing
« on: October 08, 2013, 02:28:42 pm »
Ok so I came across a new issue while trying to get more sensitivity on my Electret Mic LED trigger circuit.

To get more sensitivity as it really was not sensitive enough to get solid triggers from a distance I decided to add a second preamp stage.

So now I have a 2x NPN3904 preamp before the signal gets to the micro.  It is now sensitive and I can actually trigger it off with my voice from a few feet away.  +1 for the second stage.

The issue I have now is that the gates are staying open leaving the led lit when they should close back off.

Here is the circuit diagram of the whole setup attached.

What would I have to do to get the gates to close.  Would 10k resistors from the emitters to ground get the current to drop?

Edit: Never Mind I was able to fix the problem after a crap load of experimenting.  Turns out there was not enough Gain on the second stage.  By replacing R5 with a 6.8k resistor and adding a 10k resistor from ground to the output capacitor everything started functioning properly.
« Last Edit: October 08, 2013, 04:06:30 pm by blewisjr »
 


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