Shruthi-1 VC Filter Box Kits

Hi everyone,

Gabriel Rodrigues of Amazing Machines here, we’ve been working on this modification for our Shruthi-1 4PM and I thought that maybe people would be interested in a conversion Kit that adds CV Inputs for the VCF Frequency, VCF Resonance and VCA Level. This is by no means something that is on our to do list, we understand that the market for this thing is very limited, but if there’s enough interest from the community it might very well become a finished product one day. It’s important to notice that the range of the CV Inputs is set to /+5V on the Shruthi-1 Filter Boards (0V to 5V for the VCA) so interfacing with an Eurorack System is not exactly straight forward, it needs attenuation, it doesn’t mean that the higher voltages (Within the Eurorack Standard) would damage the Filter Board, it just needs attenuation to keep the CVs in range. Where this modification really shines is when you use a DC Coupled Audio Interface to generate CVs out of Silent Way, Volta, Max or Reaktor, because it’s spot on in range with the usual/+4.5V that a Motu Audio Interface can offer. So it can’t hurt to ask, would anyone here be interested in a kit for doing this modification?

I attached some pictures of the prototype we’ve built, I apologize for the bad pictures, these were taken from a Cell Phone.

If this becomes a Kit, our idea is to send it pre-wired as you can see in the pictures.

The Labels were carved during the Laser Cut process and I covered them with a CD Marker just to make it easily readable, doesn’t look very pretty, my bad. For a finished Kit we would want to Silk Screen the Labels and Logos.

If you know where to wire these Inputs, you will notice that I made a mistake with the Labels on this Installation, the VCA Label should be with the Connector at the Top side of the case, while the VCF Freq Label should be with the Connector at the Bottom. This way the wires stay aligned instead of overlaping.

In case you want to do this mod on your own, there’s some useful info on this forum thread:

We used a 33k resistor for the VCA Input instead of 47k, I read on another thread Olivier suggesting to experiment with resistors around 18k and 64k, it all depends on what kind of CVs you are feeding to the Filter Board, if you want them to match the range of the CV Inputs on the Shruthi-1, then you must experiment with those different resistor values, If you still have any doubt feel free to ask!

The whole idea was to give our Shruthi-1 4PM facilities similar those found on the Moog Minitaur, which can be used as a Synth on it’s own right, but also can be used as a Standalone Voltage Controlled Filter and Amplifier Box. When paired with something like Reaktor Blocks, these Inputs open a whole world of possibilities, from unlimited number of Oscillators, LFOs, Envelopes, Modulation Mixers, CV Processors to Oscillator X-Mod and Filter FM, all while keeping the amazing sound from the Analog VCF and VCA of the Shruthi-1 4PM in place.

We think that the final cost would be around $64 USD plus $24 for the Flat Rated Shipping, there would be themed Kits for the 4PM, Polivoks and maybe SMR-4 mkII boards, so what do you guys think?

Thanks in Advance!
Gabriel Rodrigues,
Amazing Machines