Check the listing for details. Mackie HM-4 4-Way Headphones Amplifier. Condition: New. Listed at 39.99 USD. This super-compact headphone amp is perfect for home studios, mobile recording, and even initimate "headphone" rehearsals. Each of the four outputs has a dedicated volume control. Input is 1/4" stereo, and each of the four headphone outputs is 1/4".FeaturesBuilt-Like-A-Tank™ constructionShare a single stereo source with up to 4 pairs of headphonesIndividual level control for each outputPowered via the included 12V AC adapterSpecificationsMaximum Level (1/4" input): +22 dBInput/Output:Input Type: Female 1/4" phono, unbalanced stereoInput Impedance: 10 kΩ each channel, unbalancedOutput Type: 4 x Female 1/4" phono, unbalanced, stereoOutput Impedance: 47 Ω each channel, unbalancedLevel Control: 4 x Rotating phones knobsPower Requirement: +12V DCCurrent Draw:Display LEDs: Top power on/offDimensions (H x W x D): 2.0" x 4.3" x 2.3"Weight: 0.5 lbs.