Found in a 1924 book by Gernsback, this circuit uses a double variable capacitor, a component not very common at the time. Listening was done on a loudspeaker at the time.
We found this circuit in a 1998 documentation. The circuit makes use of CMOS logic and must be...
Suggested by Siliconix in documentation from the 90s, this amplifier has its gain digitally...
Found in an old American publication, this is one of many possible configurations for an analog...