How do Digital Amps Mfrs. compare in sound?

I've heard good things about Rowland Continuum 500 integrated (great bang for the buck).

Stanwal -

"Digital knowledge is not power amplifier engineering." !

Class D amps are NOT digital. There is no limit to resolution. Time (duty cycle) is as analog as voltage. Analog modulator used in class D Icepower is pretty much same thing as sigma-delta DAC without filtering. Also SACD is class D (you like it or not) as well as DSD recording.

"Not a single master of analogue power amplifier engineering has turned to Class D."

Not true - Jeff Rowland for instance not only turned to class D but also stopped making anything else. This alone should suggest something.

As for efficiency - It depends what you compare to. Efficiency of class AB is not 70% - it is around 40% or less. Class A is complete disaster with 7/8 of power wasted. Just imagine true class A 1kW amp. By definition it dissipates about 15kW. Now lets look at 1kW Icepowers . They have total efficiency of 79% (including power supply). In addition music power is only a few percent of average power.

If you don't understand what class D achieves - I will try to explain. In traditional class AB nonlinear characteristic of output transistors is corrected by negative feedback. Bandwidth is increased and THD as well as IMD reduced. Unfortunately TIM distortions are introduced causing not only unpleasant sound but fatigue as well. When feedback is not fast enough to respond amplifier goes momentarily into saturation and charge is trapped on semiconductor junction of output transistors making them non responsive. Small TIM sound pretty bad with sharp sound and expanded odd harmonics but more of TIM might not be so audible. Small gaps in sound are created and our brain fills missing pieces - causing fatigue after even short listening. In Class D there is no TIM since time and not the voltage is an analog quantity.

Convenience, cost, material usage have nothing to do with class D. It just sounds great. I know - I have one.

Guido - Have you heard model 102? How do you compare it to rest of Rowland's lineup. To me it was a great improvement over integrated SS but never heard other Icepowers. Somebody said that S300 (same module as 102) sounds sweeter but less focused than REF1000.

Thank you Guido.

Muralman -

"What is the advantage of introducing a digital power supply into an analog amp?"

First of all it's not digital supply - it is as analog as class D. In fact IT IS class D (class D was invented when designers of SMPS were demonstrating that it has such fast response that it can even play music.

Advantages are few: It is line and load regulated (while linear power supply is not) and quieter (50kHz is much easier to filter out than 120Hz). Just take as an example Jeff Rowland's Capri linestage - it uses SMPS instead of linear power supply (that would be small and inexpensive) and Jeff Rowland is not a "noisy" guy (he used batteries in preamps before). Don't be fooled by size of SMPS because 2" in diameter torroidal transformer can pass as much power at 50kHz as huge 10" torroidal transformer at 60Hz.

You made already one step accepting class D. Make another one - it is the same thing.