synthCube / Ian Fritz
Chaotica Module

I built a 5U Ian Fritz Chaotica module from synthCube and modified it for +/-15V.

5U FrontPanelExpress HPGL design file



The PCB is a large format with all the IO brought out to 0.100" spacing pads.  The connector nomenclature is copper under solder mask so is a bit hard to read.


Chaotica PCB reference diagram

Chaotica 5U Mouser BOM  +/-12V standard BOM; no changes have been made for +/-15V operation




I used MTA connectors for all the IO.  This PCB has my resistor changes for +/-15V.


Ian's modification for +/-15V changes the gain of the four modulator circuits which also changes the gain of the external CV gain.  I chose to modify the gain of just the modulator controls which does not affect the external CV inputs.  I also changed two resistors that maintain the original offset for the Rate and Damping. In using the module there is plenty of range for the external CV inputs so reducing the gain doesn't really affect operation.

In addition,  I also changed two resistor to maintain the reference levels in the Reset circuit which really aren't critical.  I don't think my +/-15V modifications offer any advantage over those recommended by Ian.


My +/-15V modifications

These modifications change the gain of the four controls
Ref Orig Value New Value Comment
R51 68K 84K5
R58 270K 332K closest stocked value to 340K
R65 560K 680K
R70 180K 226K
These modifications maintain the offset for the Rate and Damping controls
R50 220K 270K
R57 1M 1.25M add 249K in series or use 2M||3.3M
These optional modifications maintain the references for the Reset input
R80 470K 562K closest stocked value to 590K
R82 47K 57k6


I chose to make the bracket as small as possible which locates the PCB very close to the front panel controls.  This made the wiring a bit difficult as the MTA connectors are along this edge.  I debated about adding an external reset button but chose not to.  I can sometimes "lock up" the module with the Clip light on but flipping switches and playing with the controls usually returns the module to operation.




Here are some XY scope images with various settings of the controls.