Found in a 90s Radio Electronics, this circuit uses a ceramic capacitor (C1) as a sensor. The operational amplifier is a double 741 of the time.
This circuit came out in an American magazine that no longer exists. It's the Electronic...
This circuit can be added to any audio amplifier design, consisting of a good tone control with an...
Using a 741 op amp with symmetrical source, this circuit was found in a 1982 documentation. The...