With the HA4000 4-Channel Headphone Amplifier, up to four people can listen to a recorded take at the same time, while being able to adjust their own individual headphone volume. High quality sound is maintained even at full volume. The HA4000 is also great to use during playing or recording, allowing listeners to hear the main mix. Max Output Level: +22dB Signal to Noise Ratio: >98dB Input Connector: 1/4" TRS Stereo Output Connector: 1/4" TRS Stereo Input Impedance: 1000KO (unbalanced) Output Impedance: Minimum 10O each channel Max Gain: 20dB per channel Power Supply: 12-18v DC adapter (included)