Up for sale are a pair of the bottlehead co crack headphones. This was a kit sold by the Bottlehead Co USA who specialise in OTL headphone amps. This started out as a pair of Monoprice headphones sold with modification components to improve and make the headphones compatible with their OTL amps which work best with high impendance headphones. The kit comprised of a high quality cable/rsisters/internal damping components to improve the sound. I purchased them complete with the kit fitted. They come with the original box etc. The sound quality quality is excellent. If you have any questions please message me. If you require any images, please send me youe email address.