Shruthi-1 Modding Session

March 22, 2013

I’ve been a bad boy, skiving-off to further molest my Shruthi-1.

These mods have been brewing for a while, as I fiddled and took notes from the Mutable Instruments forum and the Mutable Wiki. They are surprisingly easy to implement, once you gather the right components, and they are providing good learning points for the 4×4 build.

KK, on with the details…

IMG_1922

There are 3 filter switches…

  • 1. Select 2 or 4 pole filter.
  • 2. Choose either of 2 bandpass modes. I haven’t quite got this one working yet. I think I need a new switch.
  • 3. A switch to allow the audio input to be used as FM modulator on the filter. An input level knob is also added to provide more control. Initial tests of this are very promising!

And two new knobs…

  • 1. A separate FM control knob allows a degree of filter feedback. It’s quite subtle, but adds lovely harmonics to the low-end. I’m going to see if I can beef this up.
    EDIT: Thanks to the helpful guys on Mutable forum, I removed the 47k resistor and used a C10K reverse audio pot to give a nice transition from subtle to a harsher FM grit. Lovely.
  • 2. Then there is the drive knob. This one is great! It overdrives to distortion very nicely. An output volume control is necessary to attenuate, because this can get loud. Shruthi size belies and delights yet again.

I’ve also put a LED on CV1 out. This can be hooked-up in the mod-matrix to provide visual feedback of modulation parameters, including tempo-synced LFOs. It works brilliantly, and the brightness is also adjustable from the mod matrix. CV2 is also available and will be used for the same purpose. This is going to look great on the 4x4Pole!

And of course, the 2 joysticks. I am loving these. In a moment of madness I imagined an interface dominated by an army of these fellas. It surely will happen 😛

Now, I could squeeze all these entrails into the standard enclosure, but I feel that would be unfair to poor Shruthi. I’ve really gutted this guy, so it’s time to buy some new clothes, with enough space to include these and any future mods. I already partially atoned by replacing the filter caps with fancy styroflex thingies. That’s a new OLED too which makes a big difference. Finally, I took the chance to re-align the boards, and now everything is where it should be.

I’ve already designed and ordered the case: the Shruthi NoisyLitteBugger edition should be ready next week 😉

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