This sensitive 5-band circuit was found in a September 1995 issue of Electronics Now magazine. The headphones, for greater sensitivity, should be high impedance.
We have here a very interesting project found in a 1982 publication. By the operation of the...
We found this circuit in an old American manual. The formulas allow the gain to be calculated as a...
This circuit is from the time when cars used contact breakers. This 80's version measures the dwell...