Using a differential amplifier with a gain of 10 and applying the feedback after the transistor output allows for the removal of a dedicated op amp buffer and non-inverting amplifier.
Of course the potentiometer connected to the inverting input is tied to the motors shaft.
Adjusting the bottom potentiometer changes the set point which would cause the motor to spin in the direction that will rotate it's tied pot to produce an output voltage that matches the set point voltage, this would produce a differential voltage of 0V x 10 = 0V that stops the motor from rotating.
Requires a dual power supply. The circuit below is used to split a 12V source into the +/- 6V supply. Output of the transistors acts as the ground.
