This filter was found in an 80's English publication. However, it can be implemented with modern operating systems. The circuit can tune frequencies in a range from 10,000 to 1.
Found in American documentation this circuit uses transistors of the time. The circuit can be made...
The TAA300 integrated circuit is not common today. In fact, the circuit shown is from a Dutch...
This circuit was found in a 1980s documentation. Q1 and Q2 can be BC548 and SCR a TIC106. The...