Moog ladder HP mode

Fernando

Hi all,

Reviewing Moog ladder schematics in my archive I found this variation:

http://www5b.biglobe.ne.jp/~houshu/synth/moritaVCF76.gif

it includes a switch to HP mode by just injecting the input signal to the output buffer (through a trimmer and a resistor)

I like this version:
http://homepage2.nifty.com/rjb/pdf/rjb_diy_synthe_202a_vcf_moog_schem_revB.pdf

http://homepage2.nifty.com/rjb/pdf/pcb_202a_vcf_revA.pdf

http://homepage2.nifty.com/rjb/diy_synthe9.htm

and wonder if it would be possible to implement the Morita trick to get HP response...

Dan Lavin · Posted: Mon Jun 25, 2007 1:17 pm Post subject:

I'll be honest with you that high pass filters are neither something I use or am an expert at, however, I did take a peak at a couple schematics of state variable filters and they do seem to take the HPF output off of the input stage. I can also understand your attraction to this: everyone likes the Moog LPF, but likes the versatility of a state variable type. If I were you, I'd build the Moog LPF, then tack solder on the HPF mod (or breadboard) and see how it performs. If it doesn't work, you still have a nice Moog LPF. Or, you could always breadboard the whole circuit.....
Now, I do recall seeing a Moog filter with either a HPF or a BPF filter option and I don't think the circuit you listed was it. Unfortunately googling this will give you a million hits as Moog is a popular search.

I'm sure you don't like my answer. It's like when you ask a question in school and the teacher tells you to research the answer yourself and report back the results to the whole class! What you end up with is a bunch of kids who keep their mouths closed during class! Sorry, my apologies. Hopefully someone else out there is a better HPF expert.

blue hell · Posted: Mon Jun 25, 2007 1:49 pm Post subject:

goldenechos · Posted: Mon Jun 25, 2007 4:02 pm Post subject:

zipzap · Posted: Tue Jun 26, 2007 2:41 am Post subject:

I saw a schematic with the ladder in pb mode. have to look.
Basically it´s like this:
If you substract the lp from the original you get a HP.
If you substract the HP from the LP you get a BP (?)
If the filter performs very good this will sound as expected. I tried this with my moog ladder. It sounded different. That´s because the LP was not only cutting away the highs, but also changing the low signal parts in such a way, the substracting them from the original still left a lot of bass in the signal.

BTW, anyone know the sherman filterbank?
It´s got two pots to set the filterresponce.
One to blend from Lp to BP to HP.
One to blend from -BP to -BP+LP+HP
With this everything is possible, and it sounds really great. No idea how this is done, though.

goldenechos · Posted: Tue Jun 26, 2007 4:25 am Post subject:

Fernando · Posted: Tue Jun 26, 2007 5:42 am Post subject:

all very interesting info, thank you

I'm not looking for multifunction, I plan to build many different kinds of filter topologies
BTOH, Ken Stone's "CV Cluster" can be used (among a miriad of other uses) to control two filters and get variable bandwidth response a la Moog modular filter controller using an HP and a LP, etc.

I posted that schematic because I found interesting the trick.
Maybe does not give you a real HP response out of the ladder but something interesting, we'll see...
and since I do not have a Moog ladder built yet I was trying to stimulate someone to try it, since it's just a trimmer, a switch and a resistor =:)

hey, and if it works (or it does something interesting) a switched pot could be used to get intermediate responses...