OptoBox: Everyone loves (ghetto) VCAs

… because everyone loves VCAs, even ghetto ones.

Once upon a time I had a module called the OptoThing – it used an optocoupler IC to do weird and strange things to an incoming signal (side note: if you want one, you can get it as a super-easy DIY kit)

This, then, is its successor, with a bit of a difference – rather than being a Eurorack module, it is in a compact, desktop-friendly format.

There are two sides to this – there’s the ‘optocoupler side’, which uses a Sharp PC817 or similar phototransistor to do nasty, filter-like things to the sound and there’s a ‘vactrol side’ which uses a VTL5C3 vactrol to give you possibly the world’s simplest voltage-controlled filter – there’s even space for a pair of filter capacitors (I used 100nF and 10nF on the prototype builds) and a switch to swap between them. Both sides also act like ghetto VCAs, which was one of the reasons the OptoThing popped into existence in the first place. Each ‘side’ has a CV input, an input and an output – there’s absolutely nothing to stop you feeding the output of one into the other or using them both independently. There are also the obligatory LEDs which respond to the control voltage.

If you want to DIY it then you can get the bare PCB and populate it yourself:

OptoBox PCB – rear.

OptoBox PCB – top.

Construction is 100% through-hole and there are no components that cannot easily be sourced from the usual suspects – you could easily replace the vactrol with a good, old-fashioned LED/LDR combo.

You can get schematics, panel files and such from Github: https://github.com/yorkmodular/optobox

PCBs can be ordered from the Etsy store: https://www.etsy.com/uk/shop/YoMoCircuits

For partial or pre-built units, submit a custom order and we can sort something out.

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