This audio noise filter circuit is a bandpass filter for audio frequency band. It filters unwanted signals that are lower or higher than the audio frequencies.
It has 2 filters: a low pass filter and a high pass filter in a cascade configuration.
Both filters are second-order filters with a 24 dB/octave fiter capability. The 3 dB cut-off freq. are 11.8 Hz and 10.7 kHz.
The bandpass characteristic can be changed by changing the values of the capacitors and resistors. If you want to raise the bottom cut-off freq., you must reduce the values of C1 up to C4. For lowering the bottom cut-off freq. you must increase the values.
If you want to reduce the top cut-off f you must raise the values of R5 up to R8 and decrease it in order to increase the top cut-off frequency.
Audio Noise Filter Parts List
R1 = R2 = 56kΩ
R3 = 39kΩ
R4 = 100kΩ
R5 = R6 = R7 = R8 = 3.3kΩ
C1 = C2 = C3 = C4 = 0.33µF ceramic
C5 = C6 = 0.0033µF ceramic
C7 = 0.0047µF ceramic
C8 = 0.0018µF ceramic
IC1 = IC2 = NE5532N