However, as it functions right now; The amp stays literally *cool* 100% of the time. I repeated the 3 hour DVD "test" with car off, windows up that seemed , for whatever reason, to heat the amp up more than anything (music) or otherwise ever did. After 3 hours of constant usage it wasn't even warm with that fan. It's quite amazing what some airflow coming in from the cabin can do for Amp temps,.. It had to literally reduce the Amp's operating temperature by 40-50 degree's.. which is quite drastic to me.
Judging by my "Hand thermometer" I would say that amp was getting up to 80-90 degree's F. Hot enough to feel VERY warm, but not quite hot enough to be unable to leave your hand on the amp indefinitely (prior to installing the cooling fan). Now then amp can be a bit chilly as Metal will do.
Given the PPI 900.x series Class D amps, are well, Class D -- I assumed they should operate at cool temperatures and even being pressed for hours on end they shouldn't be anymore than lukewarm, not close to being "hot". I now think this is the "intended" design of these amps given with just a cooling fan introduced mine operating at max rated wattage staying so cool.
Again, to the OP, great review -- And to anyone considering PPI 900.x series amps, whether it's this amp the 900.4, 4 channel,.. or the amp I picked up for my needs the 900.5, 5 channel -- I highly recommend them. VERY affordable (My 5 channel was $209) and nice clean power. Pushing 70watts RMS x 4, and 270'ish watts (closer to 300.. x 1 for the single 10" sub) my gains are 40-50% on Front and Rear mids/highs,.. and 60% for the Sub (Which I do have at the absolute maximum this amp is rated for,.. the mids/highs I backed down ever so slightly by 0.25 to 0.5v to ensure absolutely no clipping) and I even pushed this amp at half rated wattage to all speakers just to experiment, and everything still sounded absolutely fantastic with SPL and SQ.