Using China based PCB manufacturer allpcbs, Ed previously fabcricated a couple of circuits, circuits which he typically finds useful in his designs. The first circuitboard was the Soundsniffer, which forms the basis of a preamplifier kit Ed sells via his website. The second circuitboard was a Mosfet motor driver. We utilised both circuits in our design with the addition of a pre-fabricated amplifier circuitboard for driving an 8 ohm speaker. This speaker was attached to one end of a spring, achieved by creating a small puncture in the driver, followed by pushing through a large diode which was then fixed in place using superglue.
The Soundsniffer has inputs for piezo, mic and coil pickups. A piezo was attached to end of the spring opposite to the speaker driver. It was decided that the device would feature strings so we therefore added a pair of pickups. The pickups themselves were Ed’s own design. A small fabricated PCB formed the basis of each, this attached to a bobbin fabricated using an SLA based Formlabs 3D print. Four neodymium magnets were used in each pickup (two on either side). I was particularly impressed by how strong these small magnets were.
Once the PCB, bobbin and magnets had been attached to one another we wound copper wire around each bobbin. With the help of an electric hand drill this didn’t take very long at all, perhaps around 3-5 minutes. Once wound, we were able to snap the copper wire and solder either end to the PCB, together with a cable which attached to both pickups being used. This pair of pickups was then submerged in a mixture of 80 percent paraffin, 20 percent beeswax. They were submerged for around 10 minutes. This process was used to ensure that the coiled wire did not vibrate when the instrument was being played.
A case for the pickups was fabricated using Fusion 360. We worked through the design together, each on our separate computers. After a couple of iterations we were able to create a case which consisted of a base and lid, the two snapped together and stayed attached through friction. I was amazed at the accuracy and precision of the Formlabs 3D printer. I have some experience using filament based 3D printers, which are comparatively very cost affective but not close in terms of print accuracy.