Based on the LF256 operational amplifier, this circuit was found in the September 1989 issue of Radio Electronics magazine. The indicator is analog, and the power supply must be symmetrical.
This power source, obtained in a 1973 publication, suggests the use of partially burned germanium...
This circuit was obtained from an Electronic Design from 1964. Transistors admit modern...
The circuit is from the 1994 National Semiconductor Linear Applications Handbook but can be...