Plugging it into things
Every jack, what it is for, and the Humbuster trick that fixes hum before you reach for a DI box.
05 · 6 min
Guitar into Input 1. Into a real amp, use a Humbuster cable — TRS at the Fractal end, TS at the amp — and the ground hum goes away.
The jacks
Click any jack to see what it does and what to watch for.
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 ManualHumbuster
Fractal wire their quarter-inch outputs so that a special cable — TRS at their end, TS at the amp — cancels ground-loop hum. An ordinary guitar cable works and simply gives up the benefit.
If a real-amp rig hums, this is the first thing to try, before a ground lift and long before a DI box.