ehh..I have a little bit problem on amplifier..
I'm building a circuit that can detect the voice at certain frequency range, using microphone.
I use a LM386 as pre-amp of gain 200, connected to a Butterworth Bandpass Filter, and then to a LM285 to provide further gain.
However, i found out the output is still very small, around 1Vpp. Hence i added another LM285 with gain of 10.
The things work fine if i use the input from audio generator.
However, when i use microphone, the output dowan increase 10 times as expected. Wondering why.
Another question, in a non-inversting amplifier, we increase the gain by increasing the.. resistance. Is there a limit for the gain/resistor?