Directional microphone (output to earphones) to listen birds (no bats) in quiet areas.
Today I built and tested a preamp for an electret microphone followed by a LM386 based amplifier. Both worked fairly well.
Next step is to include in between, a tunable (variable-state) filter with Gain, Q and filter mode selection available.
My questions:
1) The three stages have gain control by design. I intend to fix the filter Gain =1.
Could / should I , also fix the gain of the the preamp? If so, to what level at the output?
2) I could see in the scope that, by yelling, the electret output can reach up to 250 mV or more. While I do not expect anyone yelling around, shouldn't I consider eventual high levels as that, that could hurt my brother's ears? This is my gift to him if I manage to build something reasonable.
Is here where compression enters the game?
3) The filter requires +/-9V supply. Does it make any sense to use it also with the preamp, taking away both resistors to polarize the noninverting input when using a single supply?
4) A preamp should it be loaded with a resistor? If so what is the value?
5) The DC blocking capacitors at the preamp and filter's output, what value should they have?
Replies and also comments, are welcome. Gracias.
Today I built and tested a preamp for an electret microphone followed by a LM386 based amplifier. Both worked fairly well.
Next step is to include in between, a tunable (variable-state) filter with Gain, Q and filter mode selection available.
My questions:
1) The three stages have gain control by design. I intend to fix the filter Gain =1.
Could / should I , also fix the gain of the the preamp? If so, to what level at the output?
2) I could see in the scope that, by yelling, the electret output can reach up to 250 mV or more. While I do not expect anyone yelling around, shouldn't I consider eventual high levels as that, that could hurt my brother's ears? This is my gift to him if I manage to build something reasonable.
Is here where compression enters the game?
3) The filter requires +/-9V supply. Does it make any sense to use it also with the preamp, taking away both resistors to polarize the noninverting input when using a single supply?
4) A preamp should it be loaded with a resistor? If so what is the value?
5) The DC blocking capacitors at the preamp and filter's output, what value should they have?
Replies and also comments, are welcome. Gracias.
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