The absolute "live" sound reproduced-it's perfect, IN MY OPINION!

None,other than the ridculous controversy generated by the cost.You MUST have well matched speakers,cables/interconnects and front end to appeciate them.

I have auditioned and owned many "high" end amplifiers and for my taste, these are the perfect amps. The sound is glorius. The low end is full and goes very deep. The midrange and highs are very fast and detailed,natural. They have no problems driving my Watt/Puppy 7's. The most irritating thing about these amps is the constant complaining about the cost of these as evidenced on this site by the previous negative reviews, one reviewer giving a negative review without even listening to them. One complaining about the constuction of the amps. If the Lamm sound could be reproduced CHEAPER, why hasn't some other manufacturer done it yet? I'm sure that they have been trying in light of all the favorable reviews (many saying that they are the best amps they have ever reviewed) If you are REALISTICALLY looking for amplifiers in this price range, you owe it to yourself to audition these without bias.