my singular has finished (Singular)

by James D, Saturday, December 24, 2005, 00:01 (6669 days ago) @ Bert

I thought that a current source amp

was not sensitive to impedance at all... :confused:

Hi Bert,

With a current source style amp i.e. high or very high output impedance the series filter has no or little effect as the voltage across the filter is allowed to vary whilst maintaining more or less constant voltage across the driver due to constant current through it and so no filter effect.

To make a filter work with a current source amp you have to divert current away from the driver so the driver current develops less voltage across the driver. You do this by putting the filter components in parallel with the driver - these then divert current from the driver at the frequencies relative to the driver impedance that they become active.

So the filter has the same component values as a series filter but in parallel rather than in series...

Hope this makes sense to you!

James

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