Audio amplifier 741 (CB20478E)

This low power audio amplifier was found at 1992s Popular Electronics. Transistors are general purpose common types.

Precision Tone Switch 4046 (CB25256E)
Using a 4046 PLL this circuit recognizes a 1.6 to 1.8 kHz tone by driving an output LED. The...
Sequential Tone Recognizer LM567 (CB12669E)
In the figure we have a circuit in which the second tone recognizer remains disabled until the...
1 kHz low pass filter (CB7579E)
This filter can be implemented with almost any operational. The power suppply must be symmetrical. ...