It's been a dream of mine to build an analogue synthesizer for a few years.
In this time I've built VCOs based on the 555 timer, which I know do not generally have an accurate frequency response without a lot of additional circuitry.
I've also built a VCO based on the LM358 op-amp. This seems to sound better and be more stable.
A lot of VCO designs I've found on the internet are quite complicated to build and require the +-12v power supply. Here's an example of one designed to run on two 9v batteries inverted.
What I'm looking for is a simple design, not a huge amount of components, V/Octave frequency response and powerable by DC from a battery(or two) (with an audio frequency range somewhere between 20Hz-12.5kHz).
I'm also considering the DCO approach, the Juno method of using a programmable divider to attain a frequency from a master clock seems very attractive.