Spiral Electric FX Yellow Spiral DriveThe Greatest Show on Girth The Yellow Spiral Drive can do it all: Gain, Grit, Grind, and most important Girth. Size Matters, and the Yellow Spiral Drive allows you to control your low end content with its unique Tonehenge Girth control. The Girth control is a capacitor network selector that allows you to go from controlled lows to fit in a mix, cut through for leads, or completely unfettered low end pant rippling thunder. The Yellow Spiral Drive also