CV musings

So I have been thinking about how to easily integrate these and came up with this: two extra pots on board tapping +5V in series with normally closed TS jacks for passive volume pedals (which are just pots). Any reason this should not work? Analog filtersweep would be nice…

If you manage to solder a 30k resistor on the inverting input of the VCF CV scaling op-amp (pin 2 of IC3), you can inject there a CV signal that will be applied to cutoff in the analog domain. +/-5V is a good range for this (as this will allow you to move cutoff down to 0 even if it is set on 127 on the Shruthi-1). This is the best thing to do if you want a true analog cutoff pedal (without stepping).

I’m planning to send revised boards on friday (fixes: less noise on digital board, cleaner labeling on some parts of the PCB). I’ve just added blank pads for directly connecting analog ins on the cutoff CV path. I’m thinking of adding a jumper there so we can switch the “audio in” jack to either an audio input or an expression pedal jack.

Actually, I was thinking more about the actually “hack me” cv inputs but thanks for the input (har har). What is the resolution of the DAQ that is onboard? Would it be smoother than the digitized pots or the same? I guess what I am really after is a simple way of adding two pots by using the +5 rail and the CV inputs

There’re two ways in which you can tap into the cutoff:

  • Use a 0 to 5V signal on one of the extra CV, and route it to cutoff in the modulation matrix. Pros: can be routed to other synthesis parameters. Cons: resolution limited to 8 bits (256 steps). It’s twice as much as the digital cutoff control on the filter page (128 steps), but it won’t be truly “analogue”.
  • Use a -5 to 5V signal and push it into the CV scaler via a 30k resistor. Pros: truly analogue. Cons: hardwired to cutoff, will need some hacking unless I revise the board.

perfect, exactly what I had hoped for… :slight_smile: