If you've not come across the Look Mum No Computer YouTube channel, you're in for a treat. Sam Battle, who describes himself as a "musician and inventor", takes a high-energy approach to his videos in which he shows you how to create synths and other instruments entirely from scratch. In his latest video below, he's demonstrating how to make a Korg MS20-style low pass filter - so strap yourself in and check it out!
In amongst the manic presentation is some great advice on how to prep and build your own synth hardware - you might want to pause for breath if you're actually following along with your soldering iron - but in the end, it really works! There's more modular madness on his channel page too.