This circuit was found in a publication by Edelman from 1924. The power comes from the battery and the listening is through a high-impedance headphone.
This circuit was found in a1980s Motorola documentation. The integrated circuit is from that time....
This circuit is a variation of the previous one, indicating a voltage range, for example 11.5 to...
This circuit was obtained in a 90’s American documentation. The FET can be replaced by a modern...