A while back i posted this, and it’s been sitting on the self for quite some time! I pulled it out the other day to use as a project for my course, as an example of how cmos chips can be tricked into producing entertaining techno-esque-squelchy-ish sounds.

Its only capable of square wave synthesis, but whats the harm in that when it produces noises like this! With a few extra components you can convert the output into different wave formations, but at that point we start getting into proper synth building, so we’ll keep it simple for the time being.

Since the last post about this, I’ve been adding a few extra circuits, but kept the original which contained an interesting starve function for the vactrol. To be honest it was a complete accident that i found this, as its not your usual starve circuit that restricts the current to the output, but it works, and nothing melted, which is always nice, so it stayed.

I’ve had a few emails about this, but i’ve never documented it, which i am in the process of doing just now. So hold your horse’s, somethings coming shortly with schematics and if i get round to it…. Eagle files as well.

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.

I’ve been playing around with the square wave oscillators, alog with some ripple counters from the VGA synth, and a vactrol amongst other things, and have come up with a nice little circuit that creates rhythmical patterns.

This was wired up on a breadboard, so the switching between connections is jerky and not in sync. Expect a finished unit by the end of the week…. ish.

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I’ve been playing around with some of the IC’s I’m using for the VGA synth, to see if they can be used for audio. The circuits are based on those by Nicolas Collins, and so far, they make some brilliant sounds!

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