Ddd1, 500 watts is by no means the magical number. In fact the common 'wisdom' in this regard is 60 watts. That is to say, most amplifier topologies go downhill if the topology is built to be able to produce more than 60 watts or so.
Now most of you know that I am a tube advocate, but what you may not know is that I don't think tubes are the final answer, just that it is much easier to get them to sound like music. I've been designing and building amplifiers since the mid 1970's and I have built many transistor amps and serviced hundreds if not thousands (I used to run an audio repair operation).
So you may not agree, but you will understand when I say that I don't take most transistor amps seriously, particularly the high power ones. The best transistor amp I have heard was zero feedback, class A and made 100 watts, costing $100,000. It was made by Ridley Audio in Atlanta. It was so smooth and detailed it put most tube amps to shame, let alone all transistor amps.
Transistor amps that need not apply will be class AB and use negative feedback. I'm not quite like Julian Hirsch in saying that these amps will sound pretty much the same; there are variances depending on the power supplies, whether its bipolar or MOSFET, but in general such amps make trace amounts of odd ordered harmonic distortion which causes them to sound bright and take on a harsher character than is natural. Essentially I consider them to have a coloration, and an unpleasant one at that.
So for me the field is thus limited to tube power if we are talking 500 watts. I can count on one hand with fingers left over the number of tube amps that are contenders. Its unfortunate but that is the way it is.
