A miniature reel-to-reel magnetic tape cassette for a high speed dubbing system capable of achieving tape speeds as high as 120 inches per second or higher. The cartridge incorporates means for facilitating driving of the tape by a relatively large diameter high speed capstan, utilizes a conductive liner for preventing the build-up of static electricity at the high tape speeds employed, and incorporates self-centering concave rollers around which the high speed tape travels in passing from a pay-off reel to a take-up reel.