HOHNER Rocket 10 Hole Diatonic Amp Harmonica with Brass Reeds Plates - Key Of C In the key of C. With the Hohner Rocket Amp harmonica, Hohner has developed one of the world's loudest and most comfortable harmonica models. The green Amp version is technically identical to the standard Rocket, but features covers without side vents, which facilitates a tight enclosure when cupping the harmonica with a microphone for amplified playing. The ABS green comb with rounded sides and edges ensures a supremely comfortable playing experience and allows great control of the instrument. This is a powerful, dynamic harmonica that is perfect both for live work and recording sessions.