[Switchable ladder filter]

[Harry Bissell]

Dave: Some simulations I did indicate that you might be able to do just
that... but watch out for your supply voltages. As you add stages you need
more voltage to support it. I went to 5 stages without problems. 

The other point is where you get the resonant feedback from. I got the best
(simulated) results from taking the feedback from the last stage at all times,
and tapping the filter with a differential amplifier at an earlier stage.... I
used the 2nd and 4th stages. The fifth didn't "look" too interesting so I
didn't bother trying further. The 4th stage is "Standard M@@G", the second
stage has the same cutoff frequency, but with more pronounced "ringing".

Trying to tap the filter after the resonant feedback point is a LOSER !!! the
extra stage(s) kill any peak from the resonance... might as well not bother.

I have seen a schematic (off list) for a M@@G filter with taps at all four
stages... maybe someone has a copy they could send you... It varied the
feedback point with the tap... Didn't behave well for me. I don't know if the
schematic I saw was theoretical, or really a production unit. Someone took a
lot of time to draw (print) it, so maybe the tapped resonance worke and I'm
all wet.  :-) Harry

PS whats an fr-777 ????

"david leigh" <dave909 at hotmail.com> wrote:


Noticed that the fr-777 has a switchable 4/6 pole filter on it...
How would I go about somthing similar? is it just a matter of extending the 
"ladder" ???


Dave (Melb Australia)


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