Inputs and outputs
Every jack on the Axe-Fx III, on a diagram you can click — what it's for, and the thing about it that costs people an evening.
Axe-Fx III · Rear panel · schematic, drawn from Line 6’s panel diagram
INPUT 1 — Instrument
TS, 1/4" (unbalanced)rear panel
Your guitar or bass. This is the input with Fractal's Secret Sauce front end.
Inputs 2, 3 and 4 are line level. A guitar will make a sound in them and will not sound right — put it in Input 1.
Axe-Fx III 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 ManualFour inputs, and any of them can be a block
Inputs are placed on the grid like anything else, so one preset can process a guitar, a line source and a loop return along separate paths.
Axe-Fx III Owner's ManualOutput 1 is XLR and quarter-inch simultaneously
Same signal on both, so you can feed the desk and your amp from the same output without a splitter.
Axe-Fx III Owner's ManualHumbuster wiring on every quarter-inch output
A Humbuster cable — TRS at the Fractal end, TS at the amp — cancels ground-loop hum. Try this before a DI box.
Axe-Fx III Owner's ManualFootswitches are a separate purchase
There are none on the unit. An FC-6 or FC-12 connects over one XLR cable via FASLINK II, which also powers it.
Axe-Fx III Owner's ManualSecret Sauce is on Input 1 only
The other inputs are line level. A guitar in Input 2 works and does not sound the same.
FM9 Owner's Manual