The most important modules in an Analog Modular Synthesizer are its oscillators. Without an oscillator, there would be no sound to transform. Of coarse you could use another source of sound like a guitar or music or a human voice, but these sources have the disadvantage of not being able to be precisely controlled into constant tones, timbers and notes.
Naturally an oscillator is the first module you would want to build. Many DIYAMS websites offer their versions of a VCO. Vee-cee-oh stands for Voltage Controlled Oscillator, meaning the pitch and other functions of the oscillator can be controlled by a imputting a voltage from an external source.
CGS synth, Music From Outer Space, Thomas Henry - Birth of a synth, and Yusynth are the best producers of DIYMAS instructions and all offer one or more VCOs. I have chosen Yusynths VCO for many reasons, but it might not be the one for you. The Yusynth VCO has many features, an all Op-amp construction, a single sided PCB layout, and Mr Yusynth has a disposition to monetary gain.
Originally I bough a pack of 40 mono input jacks and plugs for the front panels before I remembered a better option. The Tinsizer, in the interest of compactness, uses 0.1 inch, double row headers in concert with solid core wires to provide patching. This is the patching method I chose for my synth, but I incorporated ground connections and shielded cables. The bottom row of the double row header are all grounds and the cables are two pronged, but for shorter patches I can just use bits of wire. I put a lot of thought into how these jacks function because of course it has to be the same on all the modules in my synth.
The three lowest knobs are attenuators which turn down the volume of incoming signals and only do anything if an input signal is fed through them, otherwise they sit dormant. I only have attenuators on my VCO's because the were the first modules I built. All subsequent models will have direct inputs, and attenuation will be patched in using external attenuators.
One of the reasons I chose this VCO was based on my theory that it would be able to achieve very low frequency's without much modification. I was able in the end to implement a switch that changed the VCO from a 4Hz - 12.6kHz audio range to a 0.047Hz(21s) - 13.3Hz LFO range (with external voltage input). These ranges are close to what I want and sound grate, it takes a lot of fiddling around with component values. I will go into copious detail in my next post about the circuit.
Possible future mods
There are a number of small problems that I may make a fuss about in the future. frequency ranges, waveform purity ect, I have a compulsion to make things perfect but that is becoming less important and rewarding then building new moduals. However would like to implement some new wave form outputs.
first would be a Ramp wave, the inverse of the saw-tooth wave would just take one opamp to make and would be very useful in LFO mode.
A serious mod I want to make is a Triangle/Saw Skew output and control. One of the wave forms of the Minimoog is a combination of its triangle and saw and helps to give its signature sound. I may also attempt to make the mix between saw and triangle, voltage controlled, a unique feature I have not seen exactly on other VCO's out there.