Shruthi-1 SDE (Sound Designer Edition) Filter ****Wiki Documentation Completed***

Martin! Please share the DIY designs if you don’t mind. I would love to see them!

Wow, I’d also like to have a look at what you’ve done.

@Titus Raindrops & piscione - no probs.

I’d made loads of notes (and measurements) along the way, but only having done the final soldering of the 6-way switches yesterday I’d yet to create neat circuit diagrams of the various mods :wink:

Leave it with me.


great work. id like to see the design, too

At this stage I’m more interested in initial reactions to the ‘sound’ of the mods - whether or not folk like them, and if so what particularly takes their fancy :wink:


Just pictures would be cool! Love to see it, even if it’s a breadboard rats nest.

I’m particularly partial to the distortion modes. I left some comments on SC…

No, it’s already neatly constructed on Veroboard :wink:

Thanks for those comments:-)


Yo yewtreemagic

interested in doing this as an old school handmade PCB? If so, drop me a Line…

love the massive texturing achieved with these mods!

Hi frank!

Thanks for the suggestion, but actually the circuitry is fairly simple (although tweaking the component values took ages for best result, and I ended up re-designing things at least three times to get maximum variation from the sounds). My board only contains a couple of dozen resistors, a handful of diodes and a couple of capacitors.

It’s the handwired 6-way switches and extra connections tagged onto the SMR-4 MkII filter board that make it more unwieldy, but I didn’t want to take the 4053/4051 route and make things more complicated :wink:


i think the resonance modes sound great. it is nice to have a choice there. (that is what i like about 4-pole, too)
the "3-SDE-Filter-FM " example has some nasty bits in it. i think its the filter fm i like there.

Good work, Martin!
Can i turn to you for advice with implementing resonance CV control of wasp filter?

In my opinion, all the versions are worth it and sounds very cool. Quite impressed by the way you’ve modified the original board.
We totally need the schemos!

Nice job Martin! I guess you don’t find yourself pining for many of the other filter boards now huh??
I attempted something vaguely similar with a x0xb0x. It sounded, umm, awful! haha. I may revisit the idea though…
Now then… I wonder if this is the table top synth under appraisal I saw mentioned on another forum? :wink:

Im curious to see how your modded Shruthi-1 SDE looks too!


Martin, was your work facilitated by the “hack” pads provided on the mkii board, or could you have modified any of the other boards just as easily?

Thanks for all your comments!

@loderbast: The existing demos are simple to demonstrate the new SDE features as clearly as possible - I only let loose a little bit more on the Filter FM demos, but I fully intend to post clips of forthcoming ‘Outer Limits’ sessions with no holds barred :wink:

@schrab: To be honest my third re-design of the Filter Flavours was after I followed the Wasp thread and listened to the MP3 clip you linked to. Although I got some new flavours as a result, ironically I got the closest to the Wasp using my Filter FM control.

@MicMicMan: My only reservation at the moment about providing the schematics is that I don’t want Olivier to lose out on any sales for his stunning 4-pole Mission design :slight_smile:

@Luap: Not quite so much pining, although I still hanker after the Polivoks for its nastiness and the SVF dual multimode :wink: And if you promise not to tell anyone else I can confirm that the Shruthi-1 is the ‘table top synth’ I mentioned another forum. As for looks, my Shruthi-1 SDE is still ‘au naturel’, but I’m working on a french polished wood and brass steampunk-inspired case.


There’s no reason not to publish the schematics. I think there are enough people in the queue for a 4PM :slight_smile:

@Titus Raindrops: I certainly used most of the existing hack pads, but I also needed to carefully add around half a dozen hand-soldered cables to various points on the back of the existing circuit board. The Filter FM pot is an easy mod using a pot wired to one hack pad and a couple of other wires soldered direct to the circuit board.

The other two mods require various hacks to the SMR-4 MkII circuitry, removing a few components, changing the value of others, as well as adding a small circuit board with extra components - I wouldn’t recommend trying them unless someone is reasonably experienced.

Filter Flavours and Shapes features could possibly be added to other filter boards, but each one would require new choices for all the resistors to match into their existing gain structures - in other words, it COULD be done, but it would require a fair amount of extra work, experimentation and measurement. Nothing I’ve done with the SMR-4 MkII is that complex - what took all the time was refining my design choices and spending many hours on listening tests to extract the last possible drop of inspiration from Olivier’s already excellent design :slight_smile:


@pichenettes: Thanks for the reassurance about publishing my circuit mods - I didn’t want to tread on any toes :wink:

I did mention to you when I first ordered my Shruthi-1 that I used to be an electronics engineer many years ago, and I would now love to give something back to this friendly community that provides so much help to other Shruthi-1 users :slight_smile: