This simple step of low power audio is from a 1975 documentation. The transistor can be a BC548, and the transformer of the type found in small transistor radios and recorders of the time.
This anti-ringing circuit was found in an English documentation from 1996. The integrated circuit is...
The figure shows how to increase the gain of the amplifier stage of the previous circuit. The...
This circuit uses unusual operational amplifiers, but equivalents can be tried. FETs can also be...