Found in a Motorola documentation from the 70s, this circuit makes use of transistors of the time. Modern equivalents can be used. The diode also supports an equivalent.
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...