February 14, 2020

Building A Drum Machine: Part I - Prototyping

This week I started the design process of building a simple drum machine. Likely, the entire module will be based around the classic Roland TR-808. The 808 is a fully analog drum kit sequencer from the early 80’s. As the story goes, it was a commercial failure. Weirdly enough, it became hugely popular not long after it was discontinued in 1983. The un-realistic drum sounds have since shaped electronic music in the same way the Fender Stratocaster has shaped rock music.

Following the schematic for a simplified version of the 808’s snare and high-hat by Total Circuit Distortion I did some bread-bording to try it for myself. I spent about 5 hours messing around with the circuit, unable to get good results. I was fed up with it and went to bed. Discouraged, the next morning I begin removing components and placing them back into their respective locations in my lab. Transistors, resistors, and finally capacitors all back into their corresponding plastic baggies, sorted neatly by value: except three crucial capacitors whose part numbers did not match my perceived values. In that moment I knew I had used the wrong sized capacitors! Instead of using 68uF ceramic capacitors, part number 683, I had used 68pF capacitors, part number 68. I was a factor of 10^6 off!

Engineering Lesson 1: Never spend too much time on one complication without a good night’s rest.