Monthly Archives: May 2014

A while ago, I made a simple synthesizer/noisemaker, with matching amplifier and loudspeaker boxes. I call it the Little Bzzztrd, which will make more sense when you hear it in action in the demo clip below :-D

A few months prior to making these boxes, I had attended Nicolas Collins‘ excellent Hardware Hacking workshop at Atelier Nord. One of the many fascinating things we learned about there was how to “misuse” a simple logic chip (a Hex Schmitt Trigger, for those interested) to make one or more nicely buzzing, square wave oscillators. At the end of the workshop I had a finished synth sporting two oscillators, with a potentiometer controlling the pitch of the first one and a light sensitive resistor controlling the pitch of the other. Which was cool enough – although the light sensitivity made it a bit unpredictable.

As I played with it, I found myself wanting more precise control and a wider selection of sound combinations. Also, I was about to make my first foray into CNC milling. So, I decided to build a similar circuit with three oscillators controlled by potentiometers, make a custom designed box for it and top it off with matching boxes for an amplifier and loudspeaker – so I could listen in style to the wonderful racket the circuit would make :-)

Since the loudspeaker box would be the simplest of the three boxes, I started with that one. I drew the design in Inkscape, with the useful Tabbed Boxmaker plugin providing the necessary calculations for generating the outlines of the parts in one fell swoop. Drawing and placing my broken note logo and the hole+pocket for the RCA connector was all that remained before the parts could be milled:

The material was a piece of grey Valchromat HDF that Jens generously gave me. I painted it before milling, to get this nice three-dimensional effect:

In hindsight, I should’ve used a different type of paint and been more thorough in my preaparatory work. I ended up using an acrylic paint, and didn’t sand or clean the surface before I painted. As can be seen in the picture above and other places on the boxes, this led to more fraying around the milling edges than necessary.

A bit of assembly:

Due to the nature of CNC milling, each tab in the corner joints had two small holes in the inner corners. Since I harvested the speaker driver from a closed box loudspeaker, I wanted to keep this custom box reasonably airtight, too. Sugru to the rescue! A bit pricey, perhaps, but still a very quick and tidy way of sealing those holes.

With that out of the way, I set about designing the box for the actual synth. This was quite a bit more complicated; with multiple connectors, holes and pockets for switches and potentiometers, a service hatch and some graphic elements. I intentionally overloaded this design, with large graphical elements and oversized switches. A loud design for a loud and obnoxious synth :-)

That last picture above is of the service hatch, which allows me to replace the battery and get at this rat’s nest of jumper cables:

Here’s the finished synth:

I wanted to assemble the final box – the amplifier – at Bitraf‘s (Norwegian language website) stand at this year’s Maker Faire Oslo. Bitraf is part co-working space, part hackerspace and part makerspace. The idea was that we would bring Bitraf to Maker Faire, instead of just showing up and displaying things we had made. This seemed to work well, both my box building and other projects attracted the interest of the Maker Faire visitors.

Here’s the finished amplifier: