If you just want the amp without building it, you can get a TPA3116 Class D amplifier. It is only $21 USD from aliexpress (with free shipping of course!). It accepts a supply voltage of up to 24V meaning that you can just dig around for your old laptop power supply (19V). It comes with a nice and sleek aluminum case, and has low enough noise floor that I can't detect it at all unless my ear is right up against the speaker. Although slightly less power output compared to the chip from the article, it gets loud enough to drown out someone yelling. This amp from aliexpress has gold plated banana plug terminals, RCA inputs, and a smooth volume potentiometer.
Link: https://www.aliexpress.com/item/Breeze-Audio-BA100-Class-D-P...