Superlux HA3D Portable Headphone Distribution Amplifier 3 independent headphone outputs with individual volume controls Frequency response from 10 Hz to 50 kHz High power outputs easily drive headphones to high volume levels with very low distortion Individual peak indicators show overload of each headphone feed. LED Battery life indicator, powered by 2 AA alkaline batteries, (10+ hours with Alkaline batteries with nominal drive levels), or an adapter with 5-17V DC output, (not supplied)