SM Pro Audio XPH4 4-Channel Headphone Amp Level 1 Input connectors: Stereo 3.5mm mini TRS and RCAMax gain: 19dB/ChannelInput impedance: 100K unbalancedS/N ratio: &gt;98dBMax input level : +22dBPower: 12-18V DC adapter (optional accessory, not included)Output connectors: 1/4" stereo TRS phoneSize: 88mm X 54mm X 38mmOutput impedance: Minimum 10 ohms each output