This is an upgraded version with Bluetooth functionality. Supports most high-impedance 16-300ohm headphones, features a 3.5mm AUX input and output, signal-to-noise ratio of 100dB, THD+N=0.0003%, effectively filtering out noise for high-quality audio performance. [Two-stage gain switch] - Enhances the signal input to the amplifier circuit to achieve optimal headphone performance. Delivers louder output with clear, realistic stereo sound and minimal distortion. [Rechargeable lithium battery] - Equipped with a 1000mAh rechargeable lithium battery, providing over 8 hours of continuous operation. Includes a volume control knob for easy adjustment. [Portable design] - Designed for on-the-go use, allowing you to enjoy music anytime, anywhere. Features a sleek and durable aluminum alloy housing for long-lasting durability. [Wide compatibility] - Compatible with various digital devices such as MP3 players, MP4 players, smartphones, tablets, computers, CD players, and personal media players. [Good sound quality] - Delivers accurate sound reproduction with a wide dynamic range, low distortion, and an expansive soundstage for detailed and immersive audio. Color: Black Material: Aluminum alloy Package Contents: 1 x Earphone Amplifier 1 x Audio Cable 1 x USB Power Cable Note: Light reflection and differences in display screens may cause slight variations in color between the image and the actual item. Measurement error allowed within +/- 1-3cm.