Inputs and outputs
Every jack on the FM9, on a diagram you can click — what it's for, and the thing about it that costs people an evening.
FM9 · Rear panel · schematic, drawn from Line 6’s panel diagram
INPUT 1 — Instrument
TS, 1/4" (unbalanced)rear panel
Your guitar or bass, on Fractal's Secret Sauce IV front end.
Inputs 2 and 3 will take a guitar and do not have this circuit. Put the instrument here.
FM9 Owner's ManualInput 1, and the Humbuster trick
Input 1 is the instrument input and carries Fractal's “Secret Sauce” circuitry, tuned for guitar and bass pickups. The other inputs are line level and will take a guitar, but without that front end. Plug the guitar into Input 1.
FM9 Owner's ManualThe quarter-inch outputs use Fractal's Humbuster wiring, which cancels ground-loop hum when you use a Humbuster cable — a TRS plug at the Fractal end and a TS plug at the amp end. An ordinary guitar cable works and simply gives up the benefit. If you have hum going into a real amp, this is the first thing to try, before a ground lift or a DI box.
Axe-Fx III Owner's ManualThe grid is the Axe-Fx III's
14 by 6, all stereo, two amp and cab pairs, eight scenes, four channels per block. For a normal preset the FM9 is not a cut-down engine.
FM9 Owner's ManualOutput 1 is XLR and quarter-inch at once
Same signal on both, so the desk and your amp can share one output.
FM9 Owner's ManualHumbuster on the quarter-inch outputs
A Humbuster cable — TRS at the FM9, TS at the amp — cancels ground-loop hum.
FM9 Owner's ManualNine switches, nine layouts
Eighty-one switch functions before you write a custom layout, which is why an FM9 rarely needs an external controller.
FM9 Owner's ManualSecret Sauce IV is on Input 1
Inputs 2 and 3 are line level. A guitar in them works and sounds different.
FM9 Owner's Manual