Found in a Popular Electronics from the 90s, this circuit can be adapted to use modern operational amplifiers. The output voltage is the square root of the input voltage.
White noise applied to an audio amplifier can be used as a relaxant, since it resembles the noise...
This circuit fires a xenon lamp being powered by a 300 V battery. The circuit is from a Radio...
The operational amplifier of this circuit is not very common today, because we removed the circuit...