Make sure to use headphones with an impedance between 25 to 70 ohms and with sensitivity as close to 100dB/mW as you can get for best performance with Iridium’s headphone output. The higher the impedance of your headphones, the lower the output volume of Iridium’s headphone output will be.
When using the headphone output on Iridium, this requires the pedal to draw more current than it normally would when the headphone output is not in use.
Iridium was designed as a an amp modeler solution in a pedal format that you can drop into any pedalboard. Like most other guitar pedals, it receives its ground connection via the 1/4″ output jacks. When listening to Iridium through the headphone output and using a wall adapter, there is no connection earth ground like there is with an amplifier. This causes some noise (hum) and is usually reduced when you ground the guitar by touching the strings. The adapter that is included with Iridium significantly reduces this hum when compared to similar parts. If an amplifier with an earth ground connection is available, then, the hum can be eliminated by connecting the LEFT or RIGHT OUT from Iridium to the input of the amplifier. The amplifier doesn’t need to be powered on for the ground to be provided. Power supplies like the Zuma and Ojai have much better filtering and isolation which will improve the noise performance.