What device receives low-level electrical input signals and amplifies them to drive the motor?

The correct answer is the servo amplifier. A servo amplifier is specifically designed to take low-level electrical input signals, such as those generated by a controller or sensor, and amplify them to a level that can control a motor effectively. This process is crucial in systems that require precise control and movement, as it ensures that the motor receives the adequate power needed to respond accurately to the input signals.

Servo amplifiers play a vital role in closed-loop control systems, providing feedback that allows for adjustments based on the motor's actual performance compared to the desired performance. This feedback mechanism is essential for applications that require high precision, like robotics or CNC machinery.

In contrast, a servo motor is the actuator itself that performs the actual movement but does not amplify the signals; it requires the input signal to be pre-amplified. A signal amplifier might increase signal strength but is not specifically designed for the control of servo motors. A power regulator is focused on maintaining a consistent output voltage or current and does not directly relate to amplifying control signals for motors. Thus, the servo amplifier is the correct choice for the function described in the question.