Normally, if you want to control the gain of an amplifier, you’ll use a variable resistor. You know, like a volume control. But what if you want to control the amplifier’s gain with a voltage? [Engineering Prof] explains a circuit that can do this using a pair of op amps and a pair of matched JFETs.
This is a companion discussion topic for the original entry at https://hackaday.com/2023/12/15/inside-electronic-gain-control/