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Operational pass band filter Q=2 BW~900 Hz, Center Fo=1850 Hz, Gain = 1.
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Suitable for speech applications where a microphone should not catch ambient noises more than expected. The Bandwidth of this filter is not really the best solution for a pleasent voice sound but separates low & high pass filters should be used instead. The microphone at the input is a capacitor capsule type, with its own voltage supply usually set at 4.5 Vdc and output impedance of about 400 ohm.
In the simulated circuit, the operational amplifier is intended to be feeded with +/- Vcc respect to ground but I suggest to use a single power supply type like LM358 . It is important to note that Q must be set for a value <10 and always greater than the stage gain.
Saying that R1 and R2 are respectively 15Kohm and 2.7 Kohm; R3 is the 33 Kohm one, we can write:
R3 = 2 Go R1 where Go is the stage gain.
R1 = Q / (6.28 F0 Go C) where C is arbitrary choosen usually in nF.
R2 = Q / (6.28 Fo C (2 Q^2 - G0)).
Remember that the Bandwidth "BW" is:
BW = Fo / F2 - F1 where Fo is the center frequency, F2 the higher and F1 the lower one.
Considering what said above, we may expect this will work nicely for women and kids voices tone ??
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