This circuit was found in the March 1992 issue of Radio Electronics magazine. The circuit has several adjustments and uses an operational amplifier. Note the supply voltage.
This circuit is used to cut the “click” in the loudspeaker of amplifiers when they are turned on....
Found in RCA documentation from the 1970s, this circuit is intended for firing thyristors in inverter...
In the figure we have the way to control a TIC series triac with a reed switch. The current in the...