The Koppophon is a special craftable Placeable item. Its blueprint can only be obtained from Banker Samael Silren's store, and it requires a unique item, Kopp's Soul Gem, to be crafted. As such, the Koppophon can only be crafted once. The item is a reference to one of Enderal's composers, Marvin Kopp. When the Koppophon's blueprint is first bought from Samael, The Prophet will receive a Mysterious Note, which points them in the direction of the unique Soul Gem required to craft this special item.
When activated, the Koppophon plays a special track composed by Marvin Kopp called "Koppophon". This grants you the "Music of the Lightborn" Steam achievement.