Erica Synths has a series of educational modules for learning about electronic music generation. I’ll be doing all of them, and we started with their EDU oscillator, then did the envelope. Next is this one, their simple VCA . Even if you don’t buy the kit, I recommend you download the user manual, it’s a great practical guide to electronics in music.
Very serviceable dual VCA, if you need more this is a good choice, easy to build and inexpensive.
EDU VCA build