The T-Rex Tremster Classic Tremolo Pedal designed to create vintage tube-amp tremolo, the Tremster uses a light-dependent resistor (LDR) to achieve its deep, buttery and seductive sound. A flashing LED displays the current speed and permits a wide range from very slow to seizure-inducing head spinning. With the Mode knob in the normal position, the Tremster has an aggressive, sine-wave type effect. Depress the mode button and the effect is less aggressive with a square-wave quality. The volume knob delivers 3dB boost in maximum position.