Class A/B versus Class H amplifiers? what is the better choice?

If you read the manual or tech sheet for the amplifier it should tell you the output topology… however that is mainly going to affect the *efficiency* that the amp will have however more efficient means less heat generation… so the circuits will theoretically be less likely to burn out from heat related stress…

you mentioned that one amplifier sounded ‘rough’… can you try to explain what you are trying to convey here? the only things I can think of is that one amplifier may 1)have a different dc filter implimented (most amplifiers have some sort of DC protection, a high pass filter probably between 1-15 hz to keep DC from the outputs), if both amplifiers have different values for this filter they may have a different very low end sound… 2)one amplifier may have been running out of power (thus increased distortion levels)… 3) (this is unlikely) if one amplifier had a very bad damping factor (damping factor is directly related to the output impedance of the amplifier) compared to the other one, you may have heard a difference in how ‘tight’ the transients were… for example, a kick drum would not punch so much as it would thud given a very low damping factor… for a well designed amp this should not be a huge issue though, the ear cannot hear the effects of damping factor (supposedly/word on the street) unless it is under ~25 (talking about the damping factor of the entire system… damping factor is *supposed* to be measured with a 8 ohm load directly attached to the amplifier output terminals (to get what the manufacturers list), speaker wire resistance and the impedance of the speaker can be used to find the actual damping factor that I was referring to.

you mentioned that the 600 watt amplifier seemed to have less improvement than you expected: remember,’doubling the watts’ gives you 3 db more spl, since you are going from 200 to 600 watts, 10*log(600/200) = 4.77 db more volume with the extra 400 watts headroom: buying a more powerful amplifier should be (IMO) for the purpose of having headroom for peaks/transients, not necessarily to make things that much louder, to double the * perceived volume* (make things twice as loud) you would need to jump from 200 watts to 2000 watts (a factor of 10)

I have no experience with yamaha amplifiers so I cannot really say regarding that. I would say look at the specifications… thd at rated power, rms power, slew rate (has more impact on high frequency response), and damping factor: along with knowledge of the dc protections on the amp, should help in predicting an amplifiers performance/comparing between models and brands

Addition: depending on the speakers you were comparing amplifiers on, you may have been hearing power compression if the 600 watt amplifier was pushing the speakers near the maximum output they can produce… so you could have been hearing the speakers running out of steam more than a difference between the amps: it would have been prudent to use a db meter and a sine tone at a certain frequency to match the output levels on the amps for a good comparison