This simple tone control using two transistors was found in an Electronics Today International of the 90s. Transistors are general purpose NPN types, like the BC549 for greater gain.
This circuit, suggested by Siemens, allows the activation of 24 V solenoids from TTL LSL signals,...
In the figure we have the way to linearize the response of a TTL port with the use of a feedback...
In the figure we have the original version of an amplifier with high input impedance, 1.2 M ohms....