Found in a Popular Electronics from the 90s, this circuit is intended to measure the harmonic distortion of an audio signal. The circuit can be tuned between 970 and 1030 Hz.
This source is used to supply circuits with operational amplifiers, being originally created for...
The transistors in this 80's documentation project may be BC548, the most modern equivalents of...
This circuit uses a FET to drive an LED with constante currente. The current up to 20 mA can be...