Most "decent" switching amps run Class A ( or at least AB ) driver stages and then run the output stage in some type of "switched" mode. They do this to maintain as much linearity as they can at the lower level stages that don't pull as much current while increasing efficiency in the output stage where it is quite current thirsty.
As to the "refresh rate", i have no idea. I remember seeing something about 800 KHz with the Sunfire amps, but that may been something about a harmonic of the primary signal. That seems AWFULLY high to me for an audio amp. Then again, such a high rate would offer greater linearity, both in and above the audible range. Sean
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