Saturday, 14 November 2015

Master Pulse Divider - CGS 22 - Build notes

These are the build notes for Ken Stone's master clock divider. Cat Girl synth 22
The incoming clock signal is divided into successive clock signals to drive EGs, sequencers, etc ... lots of nice poly rhythms.

Its more than just a simple clock divider though.
There are four outputs each for divisions of 2, 4, 8 and 16.
Altogether there are 16 outputs.
ie : each division had 4 variations that are phase shifted from each other.
The first is a straight division. As far as I can work out, each successive is shifted by 1/2 the frequency of the last. (please let me know if this is BS).
HEADERS, Beads, the odd cap & diode .

 Resistors first.

I've followed the suggested values for the resistors:
RA = 1k8
RB = 1k
RL = 2k2 (for the LEDs).

Most of the decoupling capacitors are mounted directly to the solder side of the board. Pads are provided on pin 7 and 14 of each of the 4070 for 100n the decoupling capacitors. 

 I've added heatshrink to the cap legs to avoid shorts.

 Most of the decoupling caps are surface mounted 805s.
Trannies next. These are common BC 547s

There are 4 types of IC used : the TL072,CD4024B, CD 4070B.

 It's a dual op-amp.

The CD 4024 - its a general purpose binary up counter with clock input, reset, and 7 outputs (only 4 of which are used in this circuit - Q1,Q2,Q3,Q4). The binary outputs count up on the negative edge of the clock. It counts out a binary sequence and makes the bits available on the output pins (pins 5,9,11,12).  So we clock this counter (pin 1) and this produces a binary count N bits wide. Hitting the reset (pin2) with a logic signal of 1 resets the counter to 0.

This chip is very useful if you wanna generate square waves from a oscillator.

The 4070 is the logic network which accepts the counter output bits as input.
It's a quad 2-input Exclusive-OR gate. There are 4 of these in this module.

Initial tests indicate that the pulse outputs for the CGS22 are +5v. OK for Eurorack, though my aim is to use this in Buchla land. So looks like I'll have to boost this to 10V to drive the sequencer on my 208.
The Dual Lopass Gates on the 208 do however trigger with the 5V pulses....interesting.

Update ; The Buchla 208 sequencer can be triggered with 5V pulses from the CGS 22 if you go via the Easel program card. The program card seems to accept much lower trigger voltages.
The panel is a bit rough around the edges.
The LEDS are mounted straight onto the PCB. I hate wiring things up. Couldn't avoid having to wire the bananas though. Lots and lots of flashing lights. :-)
Gotta love that.

I've wired the bananas according to divisions. The top (left most) four are division2.
The next four are division 4, and so on.... the last being div 16.
It would have been nice to mount the LEDs next to the corresponding banana, but one can't have everything.esp if you decide to mount the LEDs directly onto the PCB.

From top (left in the pic) the LEDs are labelled:
1B - Division 2 Phase 3 (clock XOR Q1)
1D - Division 2 Phase 1 (clock XOR Q1)
1C - Division 16 Phase 4 (Q4)
1A - Division 16 Phase 2 (Q4)
2B - Division 4 Phase 3 (Q1 or Q2)
2D - Division 4 Phase 1 (Q1 or Q2)
2C - Division 2 Phase 4 (Q1)
2A - Division 2 Phase 2 (Q1)
3B - Division 8 Phase 3 (Q2 XOR Q3)
3D - Division 8 Phase 1 (Q2 XOR Q3)
3C - Division 4 Phase 4 (Q2)
3A - Division 4 Phase 2 (Q2)
4B - Division 16 Phase 3 (Q3 XOR Q4)
4D - Division 16 Phase 1 (Q3 XOR Q4)
4C - Division 8 Phase 4 (Q3)
4A - Division 8 Phase 2 (Q3)

You can see a pattern developing.

+ CGS 22 build notes
+ Schematic
 + CGS version 1 
 + MOTM - Richard Brewster 
For more CGS builds, info, etc click here.

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