The HeadTAP is a passive device with an input to connect the PA or monitor amplifier and an output to connect the headphones.A volume control regulates the headphone level and internal resistors keep the unit’s impedance high enough to protect the headphones. It also protects the amplifier from encountering too low a load impedance while powering tap units, the speaker system or several tap units by themselves. A good tap will also work with a stereo headphone amplifier for use in recording situations when you want to add headphones for additional performers.