The MXR rack line of gear line began with 2-space rack units such as the MXR Model 113 Digital Delay, MXR Model 124 Dual 15-Band Graphic EQ, MXR Model 126 Flanger/Doubler, and the MXR Model 129 Pitch Transposer.
If anyone has a copy of the operation manual that shipped with this device and is willing to share it with the community, please contact us.