An analog musical oscillator is a capricious creature. It is much easier to build an oscillator for almost any other purpose than a music synthesizer. It is expected to operate over a range of up to 8 or more octaves at relatively low (audio) frequencies and it has to be able to stay in tune precisely across this range to play a chromatic scale closely enough to satisfy the very pitch sensitive nature of the human ear. This was no small engineering feat using 1970’s analog electronics. Because a synth VCO has to cover such a large frequency range it cannot be natural resonant oscillator based on a crystal like those found in radio circuits, it is generally a relaxation type oscillator who’s frequency must be driven by a precisely controlled current that is derived from a control voltage from a keyboard. And as though that wasn’t enough of a design challenge there was another problem to deal with – temperature.

Electronics are very sensitive to temperature. Much like a guitar or piano string they will go out of tune when the ambient temperature changes. When you pass a current through electronic components physics demands that they heat up. This characteristic must have given designers sleepless nights and there were many solutions invented to deal with the issue, some better than others. Tuning problems have become folklore around instruments like the Yamaha CS-80 and the original modular synthesisers from the 1970’s. Using synths in clubs where the temperature climbed during the show was always tricky for keyboard players. The one good thing that comes from this instability is that the rich sound of old synths is partly due to the subtle detuning between the VCO’s on the same voice of the instrument. Lets take a look around inside some famous synths at their VCO’s. As always, click on the images for a closer view.