32V here, just lukewarm (much cooler than a typical AB amp with a similar power rating). At idle, power consumption around 4 watts. Playing music at reasonable volume, ca. 5 watts. I suspect it runs much cooler with the 32V PSU.I've had the BT20A pro, 48V power supply for about 5 days, and I too have noticed that the amp is warm to the touch... It doesn't get unbearably hot though.
Even at idle, the metal enclosure is warm to the touch.
Playing music through a pair of KEF Q350 and running a REL Subwoofer via the Pre-Out.
The amp doesn't get warmer while playing music... just maintains the warm temp... same as when idle.
That aside, I really enjoy listening to music via this amp. I bought this after my Cambridge Audio AXR85 developed a problem.The AX85 sounds boring compared to the BT20APro. The BT20A Pro has super clean vocals, and the instruments really come alive. I love it.
Its my second Fosi amp (I also have a Fosi Audio TDA7498E)