I purchased a Fosi B20A Pro as a temporary replacement for an integrated amp that is being serviced. This is my first experience with these new little class D amps. Out of the box it sounded very bright and thin, but this thing has tone control so no problem....but after cutting the treble a bit it sounded worse. It seems the treble control cuts mids more than highs, so after cutting the treble I had a scooped out middle and piercing highs. So, I zeroed out the tone control and toed out my monitors a bunch (I also let the amp run for a few days and added the 48v power supply.) Now the system sounds great, tons of detail, really clean channel seperation, and muscular bass. Is burn in on a solid state amp a real thing? Does the power supply affect sonics? I don't know, but something happened and I like it.