Beginner Guide to Shruthi alternative control.
  • Hey team-

    I haven't gotten an enclosure on my SMR4mkII Shruthi yet, because I'd really like to add a few things. You know, stuff like in/out volume knobs, 2/4pole switch, bandpass switch, FM input mod, and maybe some CV in/out. It's the CV in/out that I'm most unsure of.

    Here's what I get:
    The IN1>-IN4> can accept 0V to +5V.
    The INs cannot control pitch value.
    The CV1< and CV2< are connected to the Filter Board but go nowhere.

    Here's where I ask dumb questions or say stupid things and you guys get to school me:
    I would like to have 4 CV IN jacks. The jacks connect to IN>1-IN>4, respectively, and GND. What about +5V? When is that applicable?
    I would like to have 2 CV OUT jacks. Can I just connect to the pins poking out the bottom of the filter board?
    For the extra CV IN FM mod, it says to add resistors. Pretty clear. Can you just feed the pin an input signal? What's the difference between sending a CV signal and an audio signal? Internal audio?
    What "protection" do I need on the CV INs?

    Okay... I think that's all of my questions. I realize it's a lot, and I'm in the deep end of the pool. Thanks for your help!
  • this thread is about making sure, cv in voltages are in the 0….5v range:

  • > I would like to have 4 CV IN jacks. The jacks connect to IN>1-IN>4, respectively, and GND. What about +5V? When is that applicable?

    It’s applicable when you want to connect a pot here instead of jacks. +5V to one end of the pot, GND to the other end of the pot ; CV to the wiper.

    > I would like to have 2 CV OUT jacks. Can I just connect to the pins poking out the bottom of the filter board?

    Yes, but keep in mind that the Shruthi-1 output PWM-modulated signals, so they can’t be fed to a modular – most modules will do something weird out of it. Better if you make them go through a glide or slew-limiter circuit… Or just a passive RC low-pass filter with a cutoff at 1kHz. If you look at the schematics of all the Shruthi-1 filter boards, you’ll see they all have such filters in place on their VCF / VCA CV paths.

    > For the extra CV IN FM mod, it says to add resistors. Pretty clear. Can you just feed the pin an input signal? What’s the difference between sending a CV signal and an audio signal? Internal audio?

    Feed whatever you want. It’s a resistor through a virtual ground so the voltage you feed is not relevant – and it can even be modular level audio.

    > CV in protection.

    A pair of schottky diodes to +5V and GND is what I now recommend.

  • Perfect. Thank you, gentlemen!