This circuit was found in a Popular Electronics from the 90s. The power source must be symmetrical and the operational amplifiers can be 741.
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...