The diagram shows a tone control with the LM381 IC. The circuit is from a Radio Electronics from February 1990. The power supply is single.
We found this measurement circuit with a logarithmic scale in an Electronics Now from November 1995....
This circuit assumes that a pulse produced by S1 has a constant duration determined by R1 and C1....
This circuit is used for remote current monitoring. In the original version of the 80s a lamp is...