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How can I calculate precisely the roll-off frequencies of this configuration? The passband seem to be between 3.1Hz to 78.1Hz. I tried using the equations for the inverting active bandpass filter but they gave different results. I can't seem to be able to get these values with any combination of values, what am I missing out?

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The passband seem to be between 3.1Hz to 78.1Hz

enter image description here

C4 and R6 define the LF cut-off and that equals 3.38 Hz

C3 and R4 define the HF cut-off and that equals 72.34 Hz

If you are measuring a difference in your sim then this is likely due to imperfections in the LM324 i.e. non-infinite input resistance. There will also be a slight effect due to C6 and R10.

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  • \$\begingroup\$ That's what I thought, just a sanity check, thank you :) \$\endgroup\$ – Shibalicious Jan 24 '18 at 12:51

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