Active filters are usually Sallen & Key designs. They work by applying positive feedback, and their input impedance is often a lot lower than casual inspection would suggest. They need to be fed from a low impedance source. In op-amp terms, that means a buffer, in transistor terms, an emitter follower, and valves need a cathode follower. Buffers should not be shared.
Failure to buffer properly is likely to cause frequency response errors and distortion in the preceding stage. That's the effect of their input impedance...
Failure to buffer properly is likely to cause frequency response errors and distortion in the preceding stage. That's the effect of their input impedance...
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