Hi, I've recently got myself an amp one which I'm mightily impressed with and have just been doing a little research on this issue as I wondered why my fan didn't come on, then I realised it doesn't have a fan! some of these appear to have a heatsink and some have a fan, I'm not sure when the change was done or why or which came first, but I have emailed AER to try and find out. Mine has a big black heatsink on the back, if you google pictures of the amp you will see the difference. I shall post when AER reply after the Easter break.