The ProCo The RAT pedal was first manufactured in 1978, and has since been used by countless artists for its simple yet unique distorted sound. It features an LM308 op-amp noted for its poor slew rate, which creates a more distorted tone despite the simple circuit's resemblance to other distortion and fuzz pedals. With three knobs for Distortion, Filter, and Volume, the RAT is the quintessential distortion pedal.