Half Wave Fast Rectifier (CB5160E)

This 80's circuit can be made with current comparators. Rectification accuracy is 1% DC up to 100 kHz.

Tunable filter amplifier (CB7237E)
This circuit for low frequencies (bass) was found in a Popular Electronics from the 90s. The...
Transistor Metronome (CB11939E)
This configuration has already been given in several articles and circuits on this website and...
Mixer 741 (CB17049E)
This circuit is a traditional mixer version with the operational 741 and appears several times on this...