Amazon.com: YGiTK Headphone Amplifier,4 Channels Mono/Stereo Metal Stereo Audio Amplifier Mini Earphone Splitter with Power Adapter 1/4" & 1/8" TRS Headphones Output and Input & AV Audio Input for Sound Mixer :
Amazon.com: Neewer Super Compact 4-Channel Stereo Headphone Amplifier with DC 12V Power Adapter for Sound Reinforcement, Studio, Stage, Choir, Personal Recording, Features Ultra Low Noise (Original Version) : Musical Instruments