AW: Re: AW: Another VCF Finished

[Haible_Juergen#Tel2743]

Hi!

I found this in my inbox, so I guess it was unsent; if it comes
twice, I am sorry.



>     I'm using 100K/220 dividers to keep the 3080 input structures in
>     linear mode. I haven't honestly done noise floor tests but I think
>     that since the filter seems to handle 10v p-p signals nicely that this 

>     will be the best way to keep the S/N high.

Yes. But maybe a little more distortion would be nice also. When I
think about how far I can overdrive this famous SSM filter, maybe
this would be nice on the 3080-4-pole as well. Could you make some
experiments with a 22k/220 divider? I think that overdriving must be
very nice, because most of the distortion would occur at the first
stage, and then the harmonics caused by the distortion would
be filtered with the remaining 3 stages. Should be very smooth!

>     Of course over the weekend I've had much time to think about this
>     filter (like in my sleep, or during dinner, etc. you know how that is) 


My wife always asks me "where are you gone? To your synthesizers??"
when I have this certain glance on my face during our meals ...

 [very good description deleted]

>     The second type however differs in that it is a unity gain integrator. 

>     This means that it can be used by itself to provide a 6 dB/octave
>     rolloff lowpass response, with no additional feedback. It is a
>     "stand-alone" integrator.

Yes. What you build this way is a current controlled 1-pole lowpass.
I am not familiar with the term "unity gain integrator". I always call it
a "Lag", but I don't know if this is precise either.

>     Since each unity-gain integrator in a multi-pole filter is
>     non-inverting, resonance is added by bringing the output back in to
>     the input of the first stage, inverted (this design does it by summing 

>     it into the (-) input of the first stage).

As you have an even number of stages, you can use either inverting
or non-inverting stages, which gives you some freedom in design.
Integrated 4-poles use inverting gm cells to reduce the required pin
number and external component count.

JH.