PreSonus HP4 4-Channel Headphone AmplifierTired of straining to hear underpowered headphones? The PreSonus HP4 headphone distribution system is louder than you're ever likely to need for session and stage use. (Be careful with that level control!) Yet the sound is clear and clean, with a wide dynamic range. At last, everybody will be able to hear! Simplicity is the HP4's hallmark. It offers left and right line inputs, left and right line outputs with level control, and four headphone outs.