Check the listing for details. Rocktron G.A.P. 1 guitar preamp rack unit. Tested. Condition: Used. Listed at 110.00 USD. The Rocktron G.A.P. 1 guitar preamp rack unit is a high-quality signal processor designed specifically for guitarists. Made by the reputable brand Rocktron, this unit offers professional-grade preamplification for enhancing the sound quality and overall performance of your guitar. With its compact rack unit design, it is easy to set up and use in live performances or studio recording sessions. The model G.A.P. 1 is known for its reliable audio processing capabilities, making it a popular choice among musicians looking to elevate their guitar sound.