This amplifier with gain control was obtained in a documentation from Signetics of the 80's. Transistors are of power and operational amplifiers are not common nowadays.
The sensor in this circuit is a BA315 diode. Other diodes can be experimented, but this is one...
This circuit tunes MW radios to apply the signal to a good audio amplifier. The circuit is from an...
This circuit can use both separate LEDs and a common cathode display when one segment indicates...