The MXR Distortion Plus utilizes a 741 op-amp to achieve its signature distortion sound, with the guitar signal entering through the non-inverting input. The op-amp's differential amplifier compares the two inputs and amplifies the difference, with gain controlled by resistor values in a feedback network.
This setup allows for a gain range from a subtle 6 dB boost to a massive 46 dB increase, depending on the resistance. However, the true magic of distortion comes from the germanium diodes, which clip the signal by only allowing voltages above 0.3 volts to pass, creating a distorted output.
This combination of op-amp gain staging and diode clipping offers a more refined and controllable distortion compared to the raw fuzz pedals of the 1960s, allowing for a range of tones from a gentle sparkle to a full-on fuzz. The MXR Distortion Plus exemplifies this elegant approach to achieving amplifier-like distortion.