Systems and methods are disclosed that can be used to control an output signal, such as for controlling a heater for a hard disk drive. A system can include a pre-driver configured to provide a pulse-width modulated (PWM) signal to an output system in response to a control signal and a feedback signal, the output system being configured to provide an output signal for driving a load, the pre-driver comprising a modulator that provides the PWM signal in response to the control signal and a filtered feedback signal. A low pass filter is configured to receive a feedback signal with a voltage corresponding to a voltage of the output signal, wherein the low pass filter provides the filtered feedback signal that controls a frequency of the PWM signal to the modulator, the low pass filter having a bulk driven operational transconductance amplifier.