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CS-style VCO core

For a  long time im interested in the sound of the old CS Synths. So I started in spring 2013 making a clone of the VCO.
After studying the Service Manuals, Interrnet Research (google Patent search) I breadboarded several circuits with more or less sucess.
Some don’t oscillate reliable, some wheren’t linear etc.

In a German Synthesizer Forum, Sequencer.de  I got help from Uwe Schüler and he designed a simple CS-Style VCO. Thank you Uwe.
I read that one of the secrets where the 30µs rectangle step.
You can see the waveform in the following pictures

CS Style Oszi1_web
CS-Style Saw


CS Style Oszi2_web
CS-Style Saw enlarged.

The VCO is a linear sawtooth oszillator with a V/Hz characteristic.
You can here the VCO in combination with my homebuild MIDI to Voltage Converter.

As you can hear, it’s detuned in the low octave. The Reason for this is the 12Bit resolution of the DAC.
In the following table you can see the small differences in the control Voltages, I think a 14Bit DAC will be fine.


CS Style VCO thru a 24dB Ladder Filter:


Note    CV
C           0V
C#        0,5297V
D          0,5612V
D#        0,5946V
E          0,63V
F          0,6674V
F#        0,7071V
G          0,7492V
G#       0,7937V
A          0,8409V
A#       0,8909V
B          0,9439V
C’         1,0000V

Here a picture  from the bench.

Aufbau 1_web


UPDATE 08.01.2014

After Uwe, the developer of the VCO, wrote me an e-mail where he asked me about the used OpAmp, i wrote him that i used an OP07 (bipolar), he told me to use jfet type.

So I changed it  to a LF356.

Here the results:

CV                   F
0.125V              49.8Hz
0.250V             99.01Hz
0.5V                 197.4Hz
1V                    393.8Hz
2V                    784.9Hz
4V                   1520Hz
8V                   3140Hz

I think this is very linear.

I did a simple temperature check (hair dryer)

15C°    1000Hz
20C°      999Hz
30C°      993Hz
40C°      984Hz
46C°      977Hz

The circuit was build with standard metalfilm resitors with +- 50 ppm

Thank you Uwe.

CS Style Schematic.pdf

Patent No. for google search:
Patent No: 3959743
Patent No: 4191932
Patent No: 4061987

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