This circuit was found in documentation from the 90s. The operational amplifier is NE5514, which is uncommon today. The configuration can be adapted to use modern components.
This filter, from an audio publication from 1977, passes the frequency range corresponding to the...
In the figure we have three voltage doubler configurations that can be used in high and low...
This circuit was found in Motorola documentation from 1966. The lamps are according to power and...