Been really busy of late with my course work, and as part of this, have turn my attention to analogue and modular synths after having so much noisy fun with the CMOS squarewave oscillators I’ve mentioned before.

I’d built a few VCO’s in the past, so a quick refresher thanks to the wealth of information available on the web has produced some amazing results!

I’ve been abusing everything from the TB style VCO’s, more simpler circuits based arround the examples from the LM13700 data sheets, to the synth-on- a-chip SN76477.

The SN76477 features a VCO, LFO, noise source with filter, attack/decay and a VCA type device. Its original purpose was to provide sound effects for video games, and it also featured in some sound effect generators and toys, but this mighty little chip has also been used in several major synth projects, such as Thomas Henry’s SNVoice module and the Super Controller, and John Blacet’s Dark Star Chaos.

There’s loads of information available on this chip to keep you entertained and building noise boxes with a handful of components, but I’m going to try and get round to building the full blown SNVoice at some point too.

On the other hand, the LM13700 is a versatile OTA chip, capable of producing VCO’s and filters amongst other things. A VCO circuit is currently on my breadboard, hooked up to a very crude CV keyboard I made to test it. It sounds pretty sweet just now without any kind of modulation from an LFO or effects.