DIMI-A cheat sheet

Only piece of original documentation that remains of DIMI-A is an A4 cheat sheet describing the instruction set of the instrument. Original version has a few mistakes in it, these are fixed on this revised version.

Band pass filter frequencies are calculated according of the components on PCBs. In real life they are slightly off because of the component tolerances. Frequencies are compromises aimed to give a peak on every A note on octaves 1-8. The original sheet lists center frequencies roughly on note F on octaves 2-9, but in reality they are not tuned that high.

Main clock circuit of DIMI-A has a limited range of where it can be tuned. For some reason HY unit is tuned one octave lower (A4 440Hz) than all DIR units and Lundsten’s unit (A3 440Hz). I suspect this to be a malfunction on HY unit which I need to get into in the future.

When A3 is tuned 440Hz, oscillator octaves align perfectly with band pass filter frequencies. In this case C0 on DIMI will be 32Hz corresponding to MIDI note 24 (C1). Here is a chart from UNSW for reference.

Here is the original sheet from 1970:

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