This circuit can be used as an amplifier for musical instruments or even with your cell phone. The circuit is old and was found in the 1990 edition of Radio Electronics Experimenter magazine.
This is the basic configuration for using the ULN2001 and MC1441 and others of the same series in...
This interesting effect circuit was found in a 1982 publication. The sequence of musical notes is...
This circuit, published in the 1980s, can be applied to operational amplifiers of almost any type....