This circuit was found in a 1924 Gernsback publication. The variable capacitors are dual. Listening is through a high-impedance phone.
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...