Found in a 1960s documentation, this circuit uses an operational amplifier from the time and a current diode, both of which are difficult to find today.
The cut-off frequency of the filter shown in the figure can be adjusted to values between...
This circuit was found in a Popular Electronics from the 90s. The components used are all common...
This circuit uses a dual floodgate MOSFET not very easy to obtain today. Its handling is very...