This elaborate mixer is from an Electronics Today International from the 80s. Operational amplifiers are common and resistors with no value determine the gain of the amplification steps.
This circuit, from the 90's, is intended for operation with vinyl record players of the time, as...
Using a zener diode it is possible to change the linearity of the scale of an analog instrument by...
Found in American documentation from the 1980s, this circuit prolongs the ringing of a doorbell or chime...