electro-music.com :: View topic - Just another Transistor Ladder Filter
Kassutronics: Transistor ladder filter
Using RC filter with transistor - General Electronics - Arduino Forum
Simple 12 db low pass filter. This filter use 2 BC547 NPN transistor and a stereo 100k pot for the cutoff, instead of … | Filters, Synthesizer diy, Transistors
DIY simple band-pass filter - Do It Easy With ScienceProg