The Marshall Modification Project

About the Project

The Marshall Modification Project explores how a largely undocumented group of amplifier technicians helped shape the sound of modern rock and heavy metal music.

From the mid-1970s onwards, rock guitarists increasingly demanded greater distortion, sustain and articulation from their amps. Commercial amplifiers of the period were not designed for these emerging guitar playing styles, and instead of waiting for manufacturers to respond, guitarists turned to independent technicians, commonly known as amp modders, to alter existing off-the-shelf amplifiers by hand. A small group of these technicians, working from small workshops and garages, particularly in Southern California, transformed standard guitar amps into tightly responsive, high-gain musical devices tuned to the desires of individual players.

One amplifier brand became central to this practice: Marshall.  Originally designed in England in the 1960s to achieve the loud live performance volume required as rock music grew in popularity and performance spaces expanded, Marshall amplifiers became the primary “donor” platform for amp mods, and a bespoke Marshall modding culture developed around the brand. Technicians such as José Arredondo, Lee Jackson and Mike Soldano redesigned Marshall amplifier circuits to meet musicians’ demands for greater gain, sustain and responsiveness, and in the process helped define the recorded guitar sounds of late-twentieth-century rock and metal.

Despite the importance of these sounds in the history of popular music, the technical and cultural role of amp modification has received little scholarly attention. The project, therefore, combines video interviews, technical analysis and cultural research to document how these technicians worked, how they interpreted musicians’ demands, and how they balanced innovation with respect for existing amplifier designs.

Central to the project is the idea of the amplifier not merely as equipment but as a collaborative musical interface. The research examines how modders describe tone, feel and responsiveness; how guitarists physically interact with modified amplifiers; and how craft knowledge and embodied listening have shaped an industry driven as much by human expertise as by electronics. In doing so, the project reveals a hidden network of collaboration between musicians and technicians that has helped define the sound of modern guitar music.