The output level at the “TO FX” (SEND) jack is controlled by the INPUT GAIN knob.

The total gain range available on the INPUT GAIN knob depends on the connector the signal is attached to and the setting of the GAIN button located on the right side of the Mixing Link, just above the “INST IN” jack. Each input connector yields different ranges for the INPUT GAIN knob.

More information can be found on page 5 of the user guide: https://s3.amazonaws.com/com.eventide.downloads/Product+Manuals/MixingLinkUG.pdf