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input impedance of active filters.q
input impedance of active filters.q
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Old 16th June 2003, 05:27 AM   #1
theChris is offline theChris
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Default input impedance of active filters.q

i was looking around at the demo of "filter solutions" and noticed each circut type has a "Zin" which has a phase, magnitude, and group-delay. so how does this affect the phase, magnitude, and group-delay of the filter?
if only it could be used for good, not evil...
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Old 26th June 2003, 12:07 AM   #2
EC8010 is offline EC8010  United Kingdom
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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...
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
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