Oscar filter board

I’ve been daydreaming about designing a clone of the Oscar filter for the Shruthi-1. I’m an electronics newb but I’m trying to fix that. Is this even a possibility or am I crazy? Here is a schematic:

There is a computer-generated diagram that is apparently based on the drawing (attached):

It’s a dual SVF done with OTAs. There’s a good chance it won’t be that different from the already existing dual SVF.

The way the biasing current for the OTAs are generated is quite original, but it doesn’t impact the sound.

if you want to do somthing with distinct sound, why not try wasp filter, randy?
there is a lot of schematics around and it looks to me (also newb) as if it was not that compilcated and quite small circuit.

Look at the Wasp’s filter schematics… It’s almost one half of the Oscar filter!

Thank you for looking at it. It was the “filter drive” parameter that seemed to really set it apart sound-wise. I thought I saw it on the schematic before but now I don’t. I guess that it boosts the osc output before the filter to send the filter into overdrive? Would it be possible to do that with the shruthi?

Haha! Yes, the oscar is definitely 2 wasp filters combined. There is a story about it here:


Actually, yes, there’s this small distortion circuit on the Wasp. Might be worth trying on a breadboard…

I’m doing it! So, I’m going to order a breadboard and all the parts that look like they match the Wasp schematic. Anything else I need? I’ve never breadboarded anything before…

Which Wasp filter schematic were you guys looking at? I found one that is hand written and some of the values are very hard to read…

that one:

Funnily this is lying in my Printer since a few days…

rhese might be interesting aswell:




Great links, thanks!

So, if I build a WASP from those schematics I’ll have a filter with several pots to control the parameters. Then there’d be the challenge of updating the circuit to deal with CV’s instead so it could be controlled from a shruthi. The Oscar design is already dealing with 5V CV’s so I would conceivably be able to connect it to a shruthi as-is and have it maybe sorta work. I could leave out one of the filters to simplify the build…

What do you guys think? Doable?

Doable. Not for me, but doable :wink:

pichenettes, is it work randy909 buying one of your Shruthi playground boards?


Ah, scrub that- I see you don’t stock that board anymore.


fcd72: Not for you why? Too hard? Am I nuts to think I can assemble a working circuit from these schematics without knowing much about electronics? (I’ve figured out enough to read the schematic - I’m in the middle of an intro to electronics book)

this one http://modular.fonik.de/pdf/Wasp%20Filter%20clone.pdf
runs already on 5v.

maybe you can get an idea from this one http://www.cgs.synth.net/modules/pic/schem_cgs49_twf.gif
how to make cv in for cutoff

The JH version is a good starting point indeed!

One thing I hadn’t notice, and which makes it differ a lot from the typical SVF is the use of a CMOS inverter instead of an op-amp in the filter core. Yikes! Spicy!