New filter boards

I have assembled today the 2 latest filter boards.

Digital filter board: it works, as in, it samples the oscillators signal and the CV accurately and without aliasing, runs “hello gain!” on the samples, and spit them on the DAC. Except that there’s no digital filter code yet :smiley: But hey, coding is a non-problem here :slight_smile:

Dual SVF filter board: it was a pain to assemble, I was scared as shit because I never got it to work correctly on the breadboard, but it appears to work. The digital routing/switching of the filter modes/serial/parallel still needs to be implemented correctly in the firmware (along with the extra menus for setting up cutoff2/res2/and all…), but I’ll work on that soon and post the first samples! This was a long battle - it’s pretty tedious to assemble and there was a board layout mistake, fortunately in a well accessible area…

Quick n00b-like question if I may… “Dual SVF” what does it actually mean? Is it 2 different types of filter on a single board, that can be modulated individually?

And while we’re on the subject of filter boards… Are you still considering the ‘modular’ board?

Dual means that there are two filters, SVF means that each of them can be configured either as low-pass, band-pass or high-pass. In addition, you can route them in parallel, in series, or in “double” mode (the output of filter 1 is sent to filter 2 but also to the main mix). So 3 modes for filter 1 x 3 modes for filter 2 x 3 routing = 27 responses. And the cutoff/resonance of both filters can be adjusted individually.

think of it as the most monstrouesque filter thingy since the Oberheim Xpander… or maybe even more monstrouesque…

Yes, that sounds good! And pretty much what I guessed it would be, and then some…
Thats going to make the random patch generator function even crazier! Brilliant!

And to think I was only going to make 1 Shruthi. Now im already considering a 4th before my 3rd is even complete…

even worse, i’m working on the 3rd before my 1st is even complete. considering some more…

Pichenettes, do you think you’ll sell kits with the digi-board + dual SVF board…I’m very, very, very, very interested…this filter looks like my beloved sherman filterbank 2…

Let’s see if there’s demand for this… But making kits means planning for large quantities! What I can say is that in terms of sound, building time, this is not a filter for everybody…

Olivier, the 2 forthcoming filters sound very exciting!

But I still am wondering about general strategy - why so many filter boards? Are people buying control boards to go with all these different filter boards, to make multiple Shruthi’s with slightly different sound characters, or are they just trying multiple filters to find the one they like best, and then just leaving the others unused, or ???

The strategy is to have fun designing circuits :slight_smile:

:) And make us all crazy in the process! :)

Seriously though - I do think it would be cool to think about a way to put all these filter boards to use, in non-Shruthi ways… Perhaps with some new project that your’re cooking up (one of the sampler ones maybe)?

Aha - I just read in the News: “A sampling synth using Shruthi-1 analog filter boards too (codename: Shruthi-612).”


Strategy strategy… Pleasure, fun, love, sunshine, …

Well done Mista O.

But where are photos? An the duck?

Sounds very exciting.
I’ll definitely be buying one of the SFVs, maybe for my Green Shruthi :smiley:

Keep up the great work, pichenettes


Well, I’m pretty sure I’ll buy one of those SVF board…


Sample 1

Sample 2

I want one !

Doesn’t seem so complicated to build looking at your photo…am i totally wrong ?

the state variable is really different. i guess you can sequence all the aspects of the filter?

and btw, is there a significant difference between the AD and the cool audio part?

Sounds great!
Put me on the list.


@rosch: you can control cutoff2/ resonance2 through the mod matrix, but not the routing/topology. Indeed, there are sometimes little plops when switching from one mode to the other so it wouldn’t be a good idea to sequence that.

The AD and CoolAudio parts are the same ; CoolAudio bought the IP from AD, and AD no longer manufactures it anyway.