They are rated at 17 volts(thx julio) and that's the worst thing about them IMO. I've heard people on this forum complain of broken amps and such, but I bought an hk401sx because I was looking for an amp I could run a .5 ohm load on, and I was so impressed with it for $200 new that I recommended it to 2 of my friends and none of the three of us have had any problems whatsoever.
Now I can't say for any of their other amps, maybe they all suck and they just did a good job with this one model, but I've heard several people on this forum who have the same amp say pretty much the same thing I am; It's a good amp for the money and it's power hungry. Of course it's not going to be on the level with some 4 grand orion or whatever, but it blows a lot of amps that cost twice as much as it does out of the water. You call it.
hehe see... sometimes people learn useful info like jerome. I wouldn't buy MA audio, but some high end models put decent amount of power, for example MA HK4000D.
i have also used a hk400d and hk800d and they both rock for the price aswell. never used anything other then their hk monoblocks. no complaints so far.
My buddy had a rockford 400 watt rms mono amp hooked up to 2 P1 12's and i hooked up my hk400d and it was way louder. And i payed 100bucks shipped for the MA amp.