So this week I finished the first edition of something I’ve been messing around with for the past few weeks: the Exenterator. It’s an oscillator that can be gated by an incoming audio signal.

This is the St. Cosmos edition – it was designed in collaboration with a vocal artist by the name of St. Cosmos, hence this edition is optimised for vocals. Here’s a quick demo (I’ll get St. Cosmos himself to upload something soon as):

There is definitely potential for some good guitar noises out of this thing too. I will be tweaking the circuit and releasing a guitar-centric edition sometime in the future but for now here’s a demo to give you a taste:

I will be producing up to ten of these units, two of which have already sold so get in touch if you would like one. They’re going for $180 each. If you’re broke like me then please go ahead and build your own: here’s my schematic and layout diagrams, and an obligatory gutshot.

If you’re interested, here’s how the circuit works: the LM386 takes the input signal and amplifies it to a level that will register on the 40106 input. The amplified audio signal is conditioned by the two inverters (IC2B and C) with the result being that the output of gate C goes high when there is an audio signal present, and low when the signal stops. IC2A is configured as a basic square-ish oscillator, with coarse and fine pitch control. D1, D2, R3 and inverter IC2D form a NAND gate (‘Mickey Mouse logic‘). This mechanism lets the oscillator signal pass through to the output only when the audio signal is present on the input. Finally the ‘mix’ pot controls the ratio between the audio signal and the oscillator signal.

Power supply note: works beautifully on a regulated power supply, but a cheap wallwart supply will cause the circuit to resonate at 50Hz intervals – I will be adding a 7809 regulator to subsequent builds to bypass this problem. Also a reverse-polarity protection diode is never a bad idea.

Let me know if you make one of these, it’s always radical to see my designs popping up round the www.

Any questions, hit me up!

FYI, the values of C5 and R2 determine the decay time on the gate.