This is an amplifier from the 70s. The integrated circuit used is uncommon today and the power supplied is not the greatest. The circuit is from Motorola.
This circuit was found in a 90s Hands-on Electronics. The transistor can be a BC548. What it does...
This circuit separates the bass from the treble in an audio signal. The circuit is from a Hands On...
The frequency of the signal produced by this circuit depends on the temperature of the diode used...