This circuit was found in an American publication in 1966. The circuit uses a general-purpose FET that admits an equivalent. The instrument is a 250 uA full-scale microammeter.
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...