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March 23, 2015 AT 5:54 am

Crowminius: a Synthesizer Story

Hey folks, Crow here.  As I may have mentioned in the past my first hobby is electronic music synthesizer design.  While a fair amount of my spare time these past two years involves the crOwBX project, I did manage to work out the design for a new instrument.  The two main driving forces behind this project were wanting to make a replacement machine in the style of a Minimoog 204D (“model D”) for my good friend Doug Ferguson, who lost his circa 1974 original Mini to hurricane Katrina, and I wanted to create a machine that would fit in the compact aluminum attache case as used with Dan Alich’s awesome Duinokit.  Thus was the Crowminius synthesizer born.  (Doug calls it “Crow’s Mini for the rest of us.”)  The schematic capture and board layout took about 10 days, with 1,457 airwires to sort through for the approximately 800 parts.  (I do not use autorouting: autorouters suck.)

Crowminius Eagle .brd

Crowminius is a compact recreation of the 204D, except my Atmel ATMEGA328P/MCP4822-based MIDI interface takes place of the old 44-note Pratt-Read keyboard.  Otherwise every control and jack on the model D is represented here.  The controls are extremely compact as the entire system has to fit on a 8.5″ x 11″ circuit board and given the inset border needed for mounting the board in the case the actual area available was 7.5″ x 10″.  Thus far all the subsystems are checking out as shown by this 98% assembled first unit.  An Adafruit LCD monitors the MIDI stream for me; that is a MIDI Note-On code for key 0x34 at velocity 0x5B.  I had a spare DAC channel available so one of the MIDI options will be filter modulation by various MIDI sources, such as key velocity.  The odd little green plastic items are actually 3D-printed clips I use on my Ikea “Detolf” figure display cases to hold NeoPixel strips to the metal struts to light the shelves.  It just so happens they clip onto pot shafts just fine for my makeshift pitch and mod wheel levers and will serve as the basis for custom printed pitch and mod levers actually meant for this sort of thing.

Crowminius v1 98% assembled

By request I added a feature the original model D did not have: PWM of the oscillators.  Oscillator #3 was typically used in “control mode” as a low-frequency modulation generator to add vibrato to the first two oscillators or additionally add filter modulation, but there was no routing to provide pulse-width modulation of the primary tone-generating oscillators.  To address this (lack of a) feature I devised a pair of simple low-frequency triangle-waveshape oscillators, one for each tone generator.  Separate oscillator PWM is one of the many details that gives the Yamaha CS-80 the rich sonic texture that made it such a great instrument, so I decided to use that concept for Crowminius PWM. Here they are being tested.

 

The only items left to install are the transistor arrays and rotary switches, then a session of calibration is in order.  Once it is all tuned up I will post some short audio demos.  Cheers!  –Crow

 


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5 Comments

  1. How much did the PCB cost?

    That looks like a monster!

  2. I ordered ten boards from seeedstudio’s “fusion” PCB service for about $250. These are 8.5″ x 11″ (216mm x 280mm) and while large, not the biggest I’ve made. About 800 parts.

  3. Robert T Wilson

    This is amazing!

    really looking forward to grabbing the PCB , will you have BOMs available also?

    cheers

    RTW

  4. Scott when the board will be available,, this looks awesome!

  5. I should have bare boards stocked in mid to late April. I am preparing online BoMs at Digikey and Mouser, and will have a google doc spreadsheet for those who need a general BoM doc. Board orders will also include a pdf of schematic and board part refdes locations, along with some assembly tips and alternate part suggestions. I will make a note here (and elsewhere) when I have boards available. –Scott

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