Using an operational amplifier of the time, this circuit was obtained from a 90s Radio Electronics. The circuit covers the frequency range from 2 Hz to 20 kHz.
This article was obtained in a French magazine Nouvelle Electronique from 1994. It can be easily...
This circuit was obtained in an old US 1974 documentation when Nixie tube displays were common. The...
This two stages amplifier is used with high impedance earphones. The transistors are very old...