Voltage Controlled Oscillator (VCO) / Low Frequency Oscilator (LFO)
Oscillator is the most basic module from which the sound begins. It can create audio frequency signal and also low frequency modulation signal for controlling another parts.
Oscillator has three waveforms: triangle, square (pulse) and sawtooth. Each of the output channel has two identical output and indicator LED. You can switching output level between unipolar (from 0 to +5V) and bipolar (from -5 to +5V)
Image of the latest released version of the module. This is not the final product, development is in progress.
You can control the frequency (pitch) by coarse and fine knobs, and also with external control voltage (CV).
- Pitch input has 1 V/Oct scale, you can tune scale by 1 V/Oct tune trim
- FM input has variable scale, controlled by Fine/FM knob in FM mode
Also for the square wave we can control pulse width by knob and by external CV.
Each input channel has two CV input pins. Signals from both inputs are summed.
Known issues
- board outline update is needed
- triangle output not implemented
- in FM mode changing FM amount affects base frequency
- expo converter has narrow range and high temperature sensitivity
- output voltage range is not quite accurate
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Hi. I would like to ask what is voltage range for the Pitch input? Is it bipolar or unipolar?
And what voltage corresponds to A4 440hz wave?
All CV voltage is in range from -5 to +5 volts, 1 V/oct.
Base oscillator frequency is tuned by pitch knob.
2 Likes
Any chance we might be able to get a sync/reset input? Would come in handy in lfo mode and who doesn’t love some hardsync.
Yes, we plan to add sync input in release version. Adding the hardsync will be simple, but I will think about softsync input also.
2 Likes
Would be there anything for a sine wave, btw?
Maybe we should have made a stretch goal out of it 
Hello!
We have a great update on the VCO schematic. I found a current leakage of about 20 µA through the Schottky diode, which caused the 1V/oct law to go out of tune, even at the second octave. After changing the diode to a BAV99, we now have 6-7 octaves perfectly tuned!
Also, the LFO range has become wider, and the oscillator can produce an ultra-long period of up to 1 minute!
Now I’m working on the triangle converter, hard sync input, and output levels.
4 Likes
After a lot of work, we’ve finished debugging the VCO module!
So, triangle output is implemented, hardsync works, output levels is 0…5 or -5…+5 with 5% accuracy!
6 Likes
