As part of the synth project, I decided to build a version of a well known voltage controlled filter (VCF). You need a VCF to make cool synth sounds! It’s what makes all those weird waaaah and woooooooh sounds and it also shapes the sound. This was not an easy task as it’s a relatively complex circuit (compared to the other parts I’ve been working on). But I made it happen in just a few days. I based my design on the work of Yusynth who is a bit of a synth DIY god. So much so Arturia contacted him for help when they built the new Microbrute. He not only published a schematic for the circuit using easy to find parts, but he also published a design for the printed circuit board (PCB). However, since I don’t have a drill press or very efficient printing techniques, I had to redesign the board… Mine is done without any holes. Instead I just soldered stuff right on the top. It’s a pretty fun way to build actually and works well enough when space isn’t a big concern. I was extremely careful in my building and got it working on the first try! Well… not really, at first I plugged the input and output of the circuit backward and had to give up around 6am this morning in frustrated exhaustion… but it worked this afternoon so I made a short demo recording. What you’re hearing is a sawtooth wave (coming from a simple design by Nicolas of Electro-Music.com) going through the filter. It does low pass, high pass, band pass and all pass, but I only used low pass and high pass in the recording. I still need to improve a couple of things, most notably, the transistors are supposed to be matched… and I haven’t done that yet. Also the power supply is supposed to be +/-15V, but I’m using some random printer power supply that’s more like +15/-17… it should sound better eventually!