Inputs and outputs
Every jack on the FM3, on a diagram you can click — what it's for, and the thing about it that costs people an evening.
FM3 · 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 circuit from the Axe-Fx line.
Input 2 is line level. The guitar goes here.
FM3 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 ManualOne amp and cab pair per preset
The clearest line between the FM3 and its bigger siblings. The FM9 and Axe-Fx III each allow two, which is what makes wet/dry/wet and two-amp rigs practical on those and awkward here.
FM3 Owner's ManualThe grid is 12 by 4
Smaller than the 14 by 6 on the FM9 and Axe-Fx III. Every slot and cable is still stereo.
FM3 Owner's ManualInput 2 is a loop return or an aux input, not both
One jack pair, two jobs. Decide which before you plan the rig.
FM3 Owner's ManualOutput 1 is XLR only
No quarter-inch pair alongside it, unlike the FM9. Output 2's quarter-inch jacks are where a real amp connects.
FM3 Owner's ManualSecret Sauce IV is on Input 1
The same instrument front end as the Axe-Fx products. Input 2 is line level.
FM3 Owner's Manual