During his employment at Serge Modular Music Systems (1980-82), Marriott invented the "voltage-controlled Casio", in which a installed circuit board allowed the keyboard to be driven by control voltage sources such as an analog synthesizer. A later upgrade used an onboard voltage source and a comparator circuit to switch between the original clock and the voltage-controlled clock. This ability to frequency modulate the Casio resulted in a wealth of bizarrely beautiful sound. Among the musicians who used this modification were Throbbing Gristle, Snakefinger, Tuxedo Moon, Don Preston and especially The Residents who purchased three of these instruments. The sound of the instrument was especially significant on the Resident's "Tale of Two Cities" and "The Mole Show" performances.

Here's the sound of the voltage-controlled Casio (together with a Serge Modular Synthesizer and other participants
Vortex (1983)