technique_valley

This circuit is the audio Amp section for a complete optical transmitter.   The circuit Amplifies and filters the voice audio signals from an electret microphone.  The circuit is described in more detail in the receiver section of Dave Johnson's.

This is a collection of inverting and non-inverting active low pass filter circuits.  I included one, two three, four and six pole filter circuits.  You can change the component value ratios shown to achieve any frequency cut-off you may need . . .

This circuit uses a switched capacitor filter IC from National Semiconductor to filter signals with frequencies higher than the 3KHz needed for voice audio. The schematic includes an audio Amplifier that is designed to drive a standard audio head phone.