High-quality, rugged construction for maximum reliability as well as easy operation which allows maximum variety of monitoring & stereo line level signal distribution options and input source select switches & phone & line 1 4" TRS stereo outputs on each channel, makes the 4-Channel Headphone Amp Line Distributor such a great asset to any professional audio system.NDYHPA4. HPA4. Nady NADY HPA-4 4-Channel Headphone Amplifier Line Distributor.