Multiple filter boards setups

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Why it is not a great idea

At the exception of the SMR4 mkII, the Shruthi-1 filter boards require special signals from CV1/CV2 and from the expansion connector to operate.

Filter board CV 1 / CV 2  Expansion port
SSM2044 High-pass filter cutoff
Digital filter CV transmission over a serial link
Dual SVF Cutoff and resonance for filter 2 Filter routing and mode selection
Polivoks Filter routing and mode selection
4-Pole Mission Filter routing and mode selection
LP2 + Delay Feedback EQ low and high levels Delay time and FX level control

As a result, it is quite straightforward to connect in parallel one of these filter boards with the SMR4 mkII; but it is not possible to connect two of the boards listed here in parallel.

If you really insist on doing it, you will have to mod the filter boards so that they don't rely on CV1/CV2 and the expansion port. Here is how it is done:


Wire a pot with A connected to 0V, B to +5V and the wiper connected to the CV1 input of the SSM2044 filter board.

Digital filter

The digital filter can only be used in parallel with a SMR4mkII. It requires a fairly complex signal on the TX> pin which can only come from a digital control board configured to operate this specific filter board.

Dual SVF

  • Wire pots to CV1 / CV2.
  • Remove the two 4053 and wire switches instead. (TODO)


  • Remove the 595 and wire switches to each of its outputs.


  • Remove the 595 and wire switches to each of its outputs.

LP2 + Delay

  • Wire pots to CV1 / CV2 and get used to the horrible control response.
  • Remove the 4822 DAC, check its datasheet, and wire voltage sources (pots, CV inputs) in place of its outputs.