This circuit is from a documentation from the 70s. The circuit uses logic gates of the time, which in many cases were arrays of transistors allowing use as audio amplifiers, as in this case.
In the figure we have a simple amplifier stage for BC547 series transistors. The gain is...
We have here a very interesting project found in a 1982 publication. By the operation of the...
The circuit shown in the figure is suggested by National Semiconductor and makes use of an...