The 741 is a bipolar op-amp sourced by many manufacturers, designed in 1968 by David Fullagar at Fairchild Semiconductor after Bob Widlar's LM301 integrated circuit design. The MXR Distortion + Operational Amplifier: The 741 When Dunlop took over MXR, the PCB was redesigned using a more modern approach to the board: the power connector, LED, jacks and potentiometers are directly mounted on the PCB, making it easier/cheaper to be mass produced.

The jacks and potentiometers are hand-soldered to the board, which makes it quite labor intense during production. All the components are placed on one side of the PCB that contains the inspiring text ' hand built by guitar players'. The original circuit is built on a single layer creme colored PCB, this PCB material was extensively used by MXR. The simple and reliable design uses only 1 operational amplifier and a pair of germanium diodes in order to create a distortion effect that boosts the guitar signal up to 46dB, with a simple mild-hump frequency response and using only two potentiometers: Output (output level) and Distortion (op-amp gain). The MXR Distortion + circuit can be divided into three blocks: Op-Amp Stage, Clipping Stage and Power Supply: The MXR Distortion + uses germanium diodes and its sound could be defined as mild fuzzy distortion, like all of the 70's rock and 80's metal recordings that made this iconic pedal famous. The design of this circuit was reliable and used later on as a starting point for the M-133 MicroAmp which is, in fact, a un-distorted redesign of this (previous) M-104 MXR Distortion+ pedal.Ĥ. Jim Dunlop bought the MXR licensing rights and currently manufactures reissues of this classic MXR distortion effect (with a power jack and an LED). The original stompbox did not have external power jack or indicator LED. The M-104 MXR Distortion + aka Distortion Plus aka D+ is a distortion guitar pedal designed by MXR and released between 19.

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