Euro-SHRUTH, the Shruthi/Phoenix MOBO for Eurorack

Hi , i have here the IDEA to build only the Shruthi Mobo as a swiss knife for the eurorack.
Only the MOBO with its outputs and signals/controls.

Signals for output are
1: the normal VCA - ADSR
2: the complete signal for the VCF separate , this means in Shruthi you can select what output you want to have.
Example , Volt(note ) output, or VCF ADSR , or the VCF LFO .
3: a output for for CV1 . In the Mod Matrix you can choose the LFO’s or the ARP or the sequencer , or all possible sources …
4: the same for CV 2
5: the oscillator singal as a separate output also.

Inputs ,
i will add a MIDI through
Note control with a normal Midi keyboard >> MIDI in
Maybe i build a Volt-to Midi interface . Than you can control the Shruthi with MODI or. switchable with Volt in/Gate.
And i make the four Volt inputs usable. This with a rail to rail Opamp…

I will make all Control voltages /output/input from 0… to 10 Volt.
This means also , the oscillator comes with a fixed filter 18 KHZ so that there is no rest of the PWM .
The other outputs also with a filter , LFO, ADSR … and so on .
The Atmel inputs get also a input 0…10 Volt . But on this inputs only pos Voltages are possible .
In the end it will be a very flexible modul with an ARP (CV out9 or stepper (CV out) ar two additional LFO and 2 ADSR
and also a MIDI to CV - if you want this .
What do you think ???

PS , the stereo Filter is also ready but i sell it at first ’ ready build ’ as a special for Christmas. Coming soon .

Let me know what you think about this .


Sounds cool!

I’m into this.

If it has v/oct and fm inputs for the oscillators it would be great! And CV inputs for modulating the parameters of the waveforms :slight_smile:

@tubeohm Hey, that was MY idea… sort of… :wink:
Go for it, sounds good to me!


How about an Ambika-style 12-bit DAC for the oscillator output?


GATE OUT would be useful too although presumably if you set the envelope to a rectangular shape this could be simulated?

Will the resolution of the LFO and ADSR outputs be noticeable if you’re modulating external VCOs?

It’s going to be 8-bit, so I imagine it will be steppy. It won’t be hi-fi generally though, so that’s not necessarily a problem.


Hi , ok possible is . Gate - no problem. You can take the VCA ADSR .
Fast attack, fast release. 100 % sustain = Gate.
But i think it is possible to use the Mod Matrix for this.
The Mod Matrix is the best . You can send nearly all LFO, Stepper, ARP to CV 1 or CV 2.
Remember for example the VCF control . This had an inbuild V/OCT .
I think it is precise enough, the normal SHR Filter works +/- 1…2 HZ.
And , you can set the V/OCT to zero - in the Mod Matrix . Than this output is a VCF ADSR .
Or this output we can also use as a LFO … and and and…
And this is only the VCF output
Hi Toneburst , can be that you also have this IDEA, i had this idea also 2 years before as i start with Shruthi, but now i have realize that there are so many options , like the both inbuild digital OSC and the Sub .
If i think more about this project it sounds for me better and better … And it is not hard to realize …
We can use the actual firmware without changes . and get a lot of usefull features.

The best will be if we can use the normal Shruthi Mobo . But maybe this needs a redesign …
I will inform you.



Will the LFO be unipolar or bipolar? If the proposed outputs are 0-10V then the LFO will need to swing around 5V for maximum range.

This LFO offset would need to be cancelled with negative offset on say a VCF or VCO

@tubeohm I was just teasing. Other people have had the same idea, too I imagine. Unlike me, though, you have the skills to actually make it happen :slight_smile:

Would you use an OLED display, and the same control layout? I wonder if it would be possible to make the interface a bit narrower. Maybe a mini OLED, plastic, knurled-shaft knobs, and mini tact switches.


I am in, too !
Go ahead André, you gonna make my day - modular tools for the win !

@tubeohm, adapting the Shruthi to eurorack is quite a big project, with a fairly small set of potential customers. Personally, I think you would be better off adapting your superb Steiner-Parker filter for eurorack. There is still no eurorack version of the Steiner-Parker filter that has solved the uncontrolled resonance problem, as you did in your Shruthi Steiner-Parker filter. That, plus the soft distortion capability, makes it the best Steiner-Parker filter available - and in eurorack format it would be really popular.

^ That.

I think you’re underestimating the amount of work necessary to remove from the firmware all the crap that will appear to be “broken” once the synth is turned into a module, then optimizing the code for more responsive CV input scanning, then redesigning the PCB for the change in output/input levels and a better UI. And how will you make the Shruthi accurately respond to CV note changes, with its 7-bit ADC? Good luck adding an external higher resolution SPI ADC…

Indeed, if you take the time to fix all the quirks of the Shruthi to make it a better citizen in a Eurorack system, you’ll end up with a shittier, less modular, underpowered version of the existing Mutable Instruments modules.

While the filter is something easy, and that people outside of this forum will actually want!

Hi Olivier ,
possible is a separate CV to midi with an Atmel 328. I don’t want to rewrite the firmware. I will use the Shruthi as it is and as additional modul for an Midi controled digital osc . With some specs more like
2 ADSR’S and the LFO and the stepper. I know that the Atmega 644 Inputs only usable for low frequency modulation . And than only with an offset. Imagine , only the Shruti Mobo with Midi in , 2 ADSR, 2 LFO and feature like your ARP , Stepper was a good start into the Eurorack system.
It was only an IDEA, here for discussion .But if i build a second PCB with the Filter and power supply units , than we can take the normal Shruthi MOBO , connect it on the new board and have the posibility to use it in an Eurorack in different ways. With CV ins and also CV outs.
Why i don’t build the Shruthacon as a eurorack version ? I simply don’t find a good solution for the front pannels- This is my biggest problem. The damn’d metal works. And less time to look intensive what tools i need to make a nice pannel . But it is in plan.
@Cnicht ,
uni polar /Bipolar with a switch . unipolad is usable for the ADSR , bipolar needs simply an Cap that removes the DC. I think a switch is an easy solution . But you had to adjust the offset in the mod Matrix . OLED , no because of the spikes of the power rail .


> I simply don’t find a good solution for the front pannels

You’ll have the same problem if you do a Shruthi euro module :slight_smile:

Andre, maybe consider making the panel out of a PCB. It’s way cheaper than a metal panel and looks better than plexi.

I have a few DIY modules with panels made of PCB material. Looks nice, I think.
I’ve only seen this done with relatively small panels, though. Cost for larger panels might not be competitive with aluminium, I suspect.


I have a couple of modules where the PCB and panel are the same thing, actually. I’m not sure that’s entirely successful, though.


It works great as long as it’s thick enough and the panel sits level on all of the jacks and pots. The Make Noise Rene is a good example. Plus it’s considerably cheaper than metal. I know from experience.