Sputnik 244 CV Toolbox

I was sent a partially built 244 CV Toolbox to finish.  I programmed the AVR parts using the STK500 and an ISP adapter.  Most of the controls are obvious except for the Manual Trigger.  These are simple CV gate outputs controlled by the switch.  The A, B, C nomenclature does not relate to the Analogue Shift Register.

 

I made PCB reference diagrams from the PCB images.

PCB1 Reference Diagram

PCB2 Reference Diagram

 

 

Operation

The Analogue Shift Register seems to be a very poor design.  Users report offset and drift problems.  I encountered both.  The amount of offset is dependent on the input voltage, so you can calibrate it at one input voltage but when you change that voltage it is no longer calibrated.  The outputs drift positive at a rate around 10 to 75 mV/minute.  These two issues make this function basically worthless.  I have no technical documentation on this module and it has that horrid black solder mask so you can't trace out the circuit.  Too bad as it should be possible to actually make this function work.

 

The Pulse Divider outputs 10V pulses as can be seen in these scope images.  These are the /2, /3, and /4 outputs.

 

These are the /5, /6, and /7 outputs.

 

This is the /8 output.

 

This is the VCA output.

 

This is the Quantizer set to 1.2V/Oct.  There is a bit of digital noise on the outputs, some of which may be due to my scope grounding as there isn't a convenient ground on the PCB.

 

 

Modifications

These modifications are from the build thread:

  1. Change R17 on PCB1 from 2M2 to a jumper.

  2. Change R117, R129, R138, and R147 on PCB2 from 4k99 to 2K (correct in the BOM)

  3. Short pins 6 and 7 together on IC14 and IC15 on PCB2.

 

 

Calibration

Calibration is straightforward.

  1. Clock the Analogue Shift Register at about 10 Hz and set the difference between the In and C output to 0V with TR1.

  2. Calibrate the V-Ref pad to 2.56V with trimmer TR4.

  3. With no input, adjust each Quantizer output to 0V with the Offset trimmers TR3, TR6, TR8, and TR10.

  4. Apply 6V to each Quantizer input.  Adjust each Quantizer output to 6V with the V/Oct trimmers TR2, TR5, TR7, and TR9.

 

 

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