It establishes the connection between the monitor signal from the mixer, instrument or amp and your own headphones. It is very easy to use: simply activate the device with the volume control and set the desired volume for the headphone signal. The RockBoard HA 1 can be adjusted to the input signal available using the stereo/mono source switch, which is easily accessible on the device. The extremely compact and lightweight aluminum housing is equipped with a clip for attaching to a belt or waistband. The HA 1 has a status LED that changes color depending on the available battery voltage. Two AAA batteries (not included) provide up to 12 hours of power and changing the batteries is done in no time at all thanks to the practical battery compartment with clip closure that is accessible from the outside. The HA 1 is equipped with a combo socket for use with stereo jacks (6.35 mm) and XLR cables for the input signal and a 3.5 mm stereo jack headphone output. On stage, in the rehearsal room or at home, the RockBoard HA 1 in-ear monitoring headphone amplifier always offers full control over the monitoring signal. In small clubs, in-ear monitoring improves the acoustics in the hall. When the band turns up the volume again, you can quickly adjust the signal and enjoy the same sound in every part of the room.