[sdiy] IR3109 (OTA-based) filter question

[>>>marjan<<<]

> 
> You should be able to get an output from each stage of the ladder in the
> 2044 using a separate diff amp.
> Have a look at Tony A's Multiladder Filter - it has an output on every rung.
> 

Yes I know that, that's what you need to do for 12/24 mode anyway, but
lees
mess (single opamp isn't the solution, so you need 3 of them per stage
or real diff amp which isn't solution for me, and times 6 for all the
voices)

> One question is whether the ladder will tolerate having the first stage
> capacitor values switched thru an analogue switch...

Now that's where OB confused me. It uses switch as you need, according
to the theory to dich that pole, so OB opted for much smaller cap
making it much farther. I don't now how ladder would react to such
thing, maybe you could eliminate cap entirely, but yes, there's also
the issue of the switch that would add/disconnect larger cap to maybe
smaller one or none (like 4066 or 4052). Note that 4th integrating cap
in OB is much smaller due to the CEM's lack of internal buffering
between stages (thanks to JH for clarifying that), and 2044 in poly6
does also have one cap smaller that others (thou IR chip in JX3P is
standard buffered so it uses all the same caps).


marjan