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…

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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 .
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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 .
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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 .

Greets
Andre’

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!

a|x

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

a|x

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.

a|x

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.

Greets

Andre’

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.

a|x

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.
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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.
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@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 .

Greets
Andre’

> 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.

a|x

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.

a|x

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.