This circuit was obtained from an 80's EDN. The components used are still common. The circuit can be used as a shield and the frequency is approximately 775 Hz.
Found in a 1968 EEE, this circuit accepts frequencies from 1 to 1000 Hz and control voltages from 0.1 to...
This circuit has appeared several times on this site in different applications. This is from 1997...
This setting appears other times in this section from other sources. This is from an 80's American...