I have been very busy with most of my spare time for the last few weeks developing a modular project (not the SDIY Experimenter!). Using lots of new ideas and techniques from recently trying to be a good bookworm!
I have developed a Voltage Controlled Oscillator and a similar concept (but simpler) Low Frequency Oscillator, a tasty Voltage Controlled Low Pass Filter based on the Sallen Key Filter concept and a Voltage Controlled Amplifier.
I have more stuff in the works as well. I am using lots of techniques which are new to me such as using transistors as voltage controlled resistors in the VCO, “vactrols” for the low pass filter and transconductance amplifiers for the VCA.
Today I started tidying up my design and prepared a pair of VCOs and LFOs on a breadboard:
I also made a test video after correcting a couple of mistakes:
The VCOs have a frequency modulating input (voltage controlled) and a soft sync input (I call it soft sync because you can attenuate the signal you sync to for a varied affect – the term soft sync is ambiguous in the world of analog synths). The VCOs and LFOs are capable of producing perfect triangle, square, sawtooth and ramp waveforms but they don’t scale to accurate musical pitches.
In the video, I patch the LFO to frequency modulate the first VCO (through an attenuator), and patch the output of the second VCO to the sync input of the first (also through an attenuator). When the second VCO is set to certain frequencies, you here a kind of stepped pitch which sounds like a musical scale.