A grounding cable has been made available as an accessory to Theremax.
In many instances, the audio output connection an amp/speaker or mixer establishes a stabilizing earth ground link with a three-prong power cord and there is no need for this cable: The circuit-common/”ground” of Theremax isn’t floating as is the situation when going into a two-prong (or battery) powered device, but anchored to the stable, zero potential of earth. This cable is useful for resolving noise conditions resulting from radiated, interfering energies introduced via the circuit-common or DC power supply’s minus pole, or other particularly sensitive circuit nodes.
Three variations for the cable allow for connection between a three-conductor wall, or power strip, outlet and Theremax (or other devices) via a connector, lug, or clip. Wire ties are included for bundling the cable along with the DC power wire.