The PA550 audio preamplifier has three selectable stereo inputs: phonograph, RCA and 3.5mm (1/8") jack for phones, tablets or other. It features a very powerful headphone amplifier so it can be used as a stand alone headphone amp. Designed to have the highest level of sound quality, whether you are using it as a headphone amp or sending music to your amplifier

The inputs and outputs of the PA550 are easy to understand. Plug a signal in, select the source, and connect to your desired headphones or amplifier. One thing to note about the PA550 is that the RCA output's are the default output. When you plug a pair of headphones into the headphone jack on the front of the unit the RCA output section is then completely disconnected from the circuit--meaning that when using the headphone output of the PA550 the unit is only functioning as a headphone amplifier.