[sdiy] Ladder filter pole

[Dave Magnuson]

At 11:30 AM 4/17/02 -0700, Tim Ressel wrote:
>Yo,
>
>I'm taking a pole: If I were to be crazy enough to
>build a ladder filter, which circuit should I use?
>

I prefer transitor ladders to diode ladders.  There's a million out there,
but they're all derived from the same design.  I'd just look for a design
that allows filter overdrive as well as voltage control of cutoff /
resonance.  It's also best to used matched transistors (match in pairs
across the ladder) and a good matched pair for the expo converter
(regardless of which design you use).  There should be tons of info about
this in the archive.

Also, it's pretty easy to add HP/LP/BP response...  If you want details,
let me know.  It would be best if you picked your filter design first, so I
can refer to specific spots on the schematic.

Dave Magnuson


PS:  building a transistor ladder is NOT crazy... I think it's one of the
"must-have" modules (I have 4 of them).  And it's easy enough to build that
it's a good diy project.  After you build your transistor ladder, it's
pretty easy to rework the PCB design to make a diode ladder...  similar
sound, but a bit smoother and not quite as much bass.  Look for EMS diode
filter schematics to see how similar it is to the Moog ladder.






Resonant Frequency:
resfreq at hoohahrecords.com
http://www.hoohahrecords.com/resfreq/index.html