VCDO-based new synth!

After the BH-101, loosely based on the Roland SH-101, I wanted a new synth.

I’ve chosen the Electric Druid VCDO as the oscillator. Despite being digital in the sense that the waveforms it produces are indeed digitally generated by a pre-programmed PIC, it is still fully CV-controllable and insert itself perfectly in the Electric Druid ‘ecosystem’ of chips, or any CV project.

So I started by building the circuit around the VCDO on a proto-board, using my now fully-adopted JST connectors for each pin, plus the associated Bessel Filters needed to convert the output of the DCO to analog.

One important thing if you want to build it is ensure that every pin must be either VC controlled, or depending on the pin, put to ground, to VCC or 2.5V if you’re not gonna control it. If not done properly, you’re just gonna end up with horrible noise out. I tried to solve this by building a dedicated proto-board, that puts the connection either to Ground, 5V or 2.5V.

Also the very important thing is to power all those modules, so I built something like this, which can distribute +12V, -12V, +5v and -5V using JST cables:

When I finally got a proper output from the VCDO, I started building the envelop and the VCA, respectively the ED ENVGEN, and the AS33XX, that I already built before for my BR-101.

So when you have a source oscillator and an envelop, you pretty much have a synth already.

The next step was interfacing this with my MIDI/CV converter, already built also, until. I’ll build a dedicated interface. When doing that you’ll have to take care of inverted CV inputs, fine tuning of voltages, but it is doable with a few op-amps and is well explained in the application schematics..

By the way, the VCDCO has 2 outputs, one Main osc and a Sub osc, so I added a simple pan pot to balance the mix between the two and from there you can pretty much add whatever you like.

For now I added an AS3320 low-pass filter, a CV controller switchable between pots and jacks from the MIDI/CV interface.
Next thing is adding an LFO, for example the Electric Druid Tap LFO, and the One Shot Env, a White noise generator to add to the two oscillators..anything is possible really.

Here are a few audio bits to demonstrate. I’m still getting some errors here and there that I have to correct. They might come from a bunch of different places, a short, bad decoupling or noisy pot..

A simple line, playing with the ADSR:

Browsing through waveforms, with Glide:

Arpeggiated, playing with ADSR:

Finally a demo track with beats:

To be continued!

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