On Tuesday, January 11, 2022 at 5:13:08 AM UTC-8, Jake T wrote:
Quick question for what I hope might be a simple circuit. I just set up
an ultra sensitive electret mic to monitor some bird activity near my residence. There was no AGC used, so when a jet flys close, it sounds
like my speakers are going to burn out from the loud sounds. Of course,
i suppose I could build an AGC, but was looking for something simpler,
maybe something that would mute the audio when a certain audio level is exceeded? Suggestions for such a circuit would be welcome. It would be
placed between the mic output and speaker. Thanks in advance.
There's an integrated circuit, LM13700, that has this basic function.
See figure 17 here
<
https://www.ti.com/lit/ds/symlink/lm13700.pdf>
That example uses one half the chip, and responds to pulling the 'gain control' pin low
when the sound is too loud. The tricky part is, you use the other half of the chip
to amplify, rectify the sound from AC to negative DC, smooth the DC with a capacitor,
and steal some current from the "Iabc" circuit node while that capacitor
stays negative. It's just a couple of capacitors, diode, and a lot of fiddling with
resistor values.
Alas, it's an oddball chip, and an oddball kind of design.
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