The efficiency of a heat sink can be greatly improved by disturbing the boundary layer that forms at the heatsink/air interface. It's like wind chill. This doesn't take much. Measure the temperature of the heatsink and then gently move the air around it with a folded paper fan and measure the temperature again. You should see the temperature go down substantially. It will give you an idea of how little air movement is needed and a full fan, like those in a PC, is not needed as you do not have an enclosure that would trap the heat.
How hot is too hot?
I am running a Gryphon Diablo 300 to drive a pair of Magico A3. My room size is around 3m*4.5M. I usually listen at around the 80db level, mainly to jazz and classical music.
My room temperature is almost always kept at 26 degrees Celsius in the summer. After operating after an hour or so, the heat sinks of the 300 often gets up to 50 degrees with the top cover at 38 degrees. My dealer told me these temperatures are normal but I feel this is hot (too hot?).
I should also add that the amp is placed on the top of a flat open shelf so there is no question on ventilation.
Any experience by other Diablo 300 users to share?
TIA!