This one was a request. Two pots onboard and one offboard. The Barbershop Overdrive is a transparent overdrive/booster with medium gain. It has the expected Volume and Drive controls, but also has a Sag control which alters the voltage the pedal is running at. This can change the color and compression of the tone.
I did a little research, and found out Q4 is just a fancy way of doing polarity protection and can be omitted if you want. Here's a layout without it.