Installed a volume knob. Built-in amplifier electric guitar. Sound is produced by a 9V rectangular battery. The sound from the built-in speaker and the external output jack is good, with no scratchy noise. The back cover didn't fit, so it has been modified. The neck is straight. The string height has been adjusted to a suitable level. There is no fret buzz or dead notes. There are scratches due to it being a used item. Please purchase with the understanding that this is a used item.