PAM8403 mini amplifier: 2.3 x 1.8cm / 0.9 x 0.7in, compact size fits easily into small spaces in various digital devices, high amplification efficiency. Powered by 5V USB from computer, phone charger, or lithium battery. High efficiency up to 90%, delivers 3W (left channel) + 3W (right channel) output with 4-ohm load and 5V power supply. Class D amplifier design ensures high efficiency, maintains sound quality without thermal degradation, no heat sink required. Built-in noise reduction circuit eliminates popping noise during power on/off, supports short circuit, over current, and over temperature protection. Specifications: Working Voltage: 2.5V5.5V DC (do not exceed 5.5V, observe correct polarity) Compatible Speaker: 48 ohm (4 ohm recommended), speaker power 28W Color: Green Material: PCB Package Includes: 5 x Power Amplifier Note: Light and display settings may cause slight color variation between image and actual item. Measurement error allowed within +/- 13cm.