The Art of Creating a High Pass Filter
Our goal was to produce a high pass filter using a hand wound inductor created in class. We wanted to achieve around 2mH of inductance so that we could use a 3 to 5 Ohm resistor in the RL network.
To wind our inductor all we needed was 120 or so feet of bobbin wire, a piece of 1 inch diameter PVC, some hot glue and a whole lot of patience. Our best inductor was produced by one of my patient students; I call him, “Rock Solid” because he has nerves of steel. He was able to get a value of 1.937mH or so. Not bad considering there was in the neighborhood of 400 turns, all of which had to be meticulously wrapped and aligned. We wanted a cutoff frequency of around 300HZ which lead us to our resistive value of 3.7 Ohms. All frequencies below 300 Hz would be essentially blocked, while those above 300 Hz would be passed. We were then able to plot the voltage magnitude out with respect to frequency. This showed the cutoff just as expected. It was a great learning experience for students in hands on precision component fabrication as well as protoboading. Hand wound is the method used for high-end speaker crossover networks.