I've got 2 of them and think its a great amplifier. I don't agree with the "heavy as snot" comment in a previous post because I swapped to the AP4k from Yorkville AP6040's and as a result my amp racks lost 26 lbs each. At 41 lbs it seems to be about the same weight as comparable power amps. The only issues I have had it that it seems to be more power hungry than it's predecessors. I don't think I every tripped a circuit breaker in my distro with the 6040's but have done it several times since swapping to the AP4K's. Keep in mind that when I have tripped a breaker during a gig I was hammering the subs so it wasn't a complete surprise. For some reason I have also had them to trip circuit breakers on initial power up but when it's done this I've just turned amp power switch off, re-set the breaker, and repeated power up and it was fine. My only other gripe is that the knobs stick out a bit far and I feel like they are vulnerable to damage because of this but I have no evidence to prove it. I REALLY like the fact that I can choose to have full power at either 2 or 4 ohms per channel. This feature gives me a lot of setup flexibility and since a lot of the time I'm going into a situation blind it's nice to be able choose. I've had mine for almost 2 years and probably 100 shows and have had no issues.
