Mackie HM-4 Headphone Amplifier 4-Way

Compact 4-Way Headphone Amplifier Share a single stereo source with up to 4 headphone pairs, 1 x 6. 3 mm jack stereo input and 4x 6. 3 mm jack stereo outputs with individual volume controls, Dimensions: 51 x 109 x 58 mm, Weight: 200 g, Includes 12V ... To my ears it slightly brightens the sound, but I use it in specific scenarios so take this with a grain of salt.

I got it to raise the volume of backing tracks when I'm drumming on my electric drumset, did the job. I found myself using it to listen to music on my tablet with the studio headphones, WOW It's now my favorite way of listening to music, when I want to hear the details. Easy method to get loud headphone volume and drive multiple headphones from a single box.

Mackie made a very good product. The grounding in the power supply isn't the greatest so you'll get a lot of electrical noise coming through if you have this near several other power cables but easy enough to navigate around if you just move it a bit. Other than that, this thing can push headphones stupidly loud, and the quality remains perfect until about 80% or more and then you get audible distortion, but at that level you're definitely damaging your ears anyway!