DroneBox: Square Wave Shenanigans

Building a square-wave oscillator from 1/6 of a 40106 hex Schmitt trigger is a bit like the ‘Hello World’ of synth DIY, and for good reason – you don’t need a huge number of parts in order to get an audible result. Instant gratification, and all that.

Things get a lot noisier when you start mixing multiple oscillators together, and if you take it a step further and mix the oscillator outputs through a CMOS logic IC such as the 4070 quad XOR, then you’re really starting to cook.

That’s what the DroneBox does.

It is essentially a tarted-up version of my XO106 Eurorack module – a square-wave drone generator with individually tunable (hoho!) oscillators mixed through a logic IC. To increase the sonic palette there’s also a current starvation pot, which makes the 40106 behave very oddly in some cases, and a simple RC filter to knock the rough edges off the sound should you see fit.

Whereas the XO106 is a Eurorack module built with surface-mount componentry, the DroneBox uses 100% through-hole construction – this confers two distinct advantages: firstly, and most obviously, it’s a good DIY project (yes, PCBs are available). The second reason is a bit less obvious – since through-hole ICs are used, you can swap out the logic IC for something that’s pin-compatible.

What does this mean?

It means that you don’t have to stick with the CD4070 if you don’t want to – whilst it produces some very nice, metallic sounding drones, there are times when you may want something a bit different. This being the case, you can swap the 4070 out for another CMOS logic chip in order to change the timbre of the output – you can use a 4001 quad NOR, or something like a 4011 quad NAND or 4093 NAND Schmitt trigger. Good, eh?

But wait! There’s more …

 The desktop version of the module has a set of switches – one per oscillator. Depending on the size of the capacitors you use this enables you to have a ‘low’ and a ‘high’ range for each oscillator – this means that by using a capacitor of 10μF or so on one of the oscillators you can get some really cool gating/LFO type effects. If you’re DIYing, the choice is entirely yours.

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