Well 220mA @ 5v is only like 1.1W, I think a LM317 is good to about 1.5A so not sure why you’re getting that much heat? The voltage differential is ok.
As you say, try a heatsink, it should get warm but not burning hot.
But you are trying to dissipate 4W (25-5V) 0.2A no wonder it is getting hot - too much voltage differential
Yes it works ok with the heatsink, not really the most efficient way of doing it though as the regulation is wasting 4x the power the board draws…I’m ordering the external DAC and when I get that I’ll move back to the DC-DC converter.
I’m also converting another of these amps with the pro board for another room, so will be interesting to see if that has the same issues.
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