my ppi a600 gets really hot

hey guys, decided to try my old sub amp for my mids/highs so i hooked it up, speakers sound great with it. only problem is the amp is geting very hot. this is after listening for 15 mins. i dont remember it getting this hot before when i used it to power my subs. i am running alpine spx177a. i have the mid range and the tweets wired to the x/o's and then to the PPI amp. i dont have them bridged or anything. i was thinking bridging it would change the ohm load the amp will see. anyone have this problem with this amp in the past?

Turn the amplifier on but leave the volume of your deck at zero.  Leave it on for the 15 minutes and let me know if it is still getting hot.