This circuit is from an ancient American documentation. The integrated circuit is 741 and the power supply must be symmetrical. The passing band is centered at 1 kHz.
The components of this circuit are exchanged for modern equivalent such as 470 K for the pot and...
This voltage regulator for automotive use was found in a Radio Electronics from the 80s. The Q3...
This circuit was obtained from an English magazine from 1979, but can be easily assembled today...