The ZK-ST21 is a premium-quality 2.1 Channel Bluetooth Digital Amplifier Board designed for those who demand high-power, crystal-clear audio performance. Featuring the advanced Texas Instruments TPA3221 Class-D amplifier chip, this board delivers 100W RMS per stereo channel and 200W RMS for the dedicated subwoofer channel — giving you powerful, distortion-free sound for your home theater, multimedia, or DIY speaker projects.