"D" amps, general discussion who's 1 and why?

Ok, the AR Ref3 will be a good match for 501s. You might read Guidocorona's review of the Rowland Capri, where he moved from the Ref3.

PFC is an interface with the mains that Rowland uses to present an even load to the mains and convert the AC line to 380 Volt DC for the amps. It's designed for certain recent Rowland models, including the 501s. It's built into the 312 and the Continuum 500, but can be had as an add-on to the most other current Rowland products. (The PFC units that Rowland uses were originally developed for commercial cell-tower equipment by cell phone companies).

You need to talk some directly with Guido. I have no direct Ref3 experience, but he can discuss the pros and cons of moving away from the Ref3 to Rowland, since he made that move it.

Dave

Cardas Golden Ref works well with Rowland, giving no "hiss". I don't use it, but I've heard it in Rowland systems a lot. There could be a number of reasons for the differences noted. For instance, not all Class D has managed RFI and EMI as carefully as Rowland and some others. Chassis design for optimal isolation and ground management is critical with Class D.

Dave

With all the mention of the Rowland products I'll chime in here with my experience. I use the CONCERTO integrated with outboard PC-1. Amps before this include the McIntosh MA-6900, Cary Cinema 5 (excellent by the way), Rowland Concentra, and McIntosh MC-300. I've had the same speakers across all of these amps save the MC-300. Speakers are Tyler Linbrook monitors.
The Rowland Concerto is superb. Compared to all of the other amps I've had it loses nothing. Detailed, not cold, not warm, excellent noise floor (low) and dynamics. I will say that when I added a Shunyata Hydra things improved even moreso. I have read here from other posters the same experience. Not sure why, but it did. With the PC-1 and Hydra, the Concerto is fantastic. I have tried the Concerto without either the PC-1 or the Hydra, and it's still 95% (speculative enumeration!)of the way there.
I recently tried this system with a pair of Proac D25's, and the sound was similarly fantastic in all the areas you would ask about - soundstaging, midrange, etc, however the treble was too 'hot' for my tastes. I breathed easier when I put the Tyler's back in. Now lest someone say obviously the Tyler's somehow are not up to the task, I'll add that the last head-to-head I had in my system was the Harbeth SHL-5, which did NOT have any bright treble issues with this amp. It was truly spectacular. (My post is here elsewhere on the differences between the Harbeths and Tylers). I have yet to find a speaker that I have auditioned (save some bigger Wilsons and ML Summits) that did more for me than the Tyler's, and many less. Anyway, as far as the class D amps in my experience, I recommend them. If mine was cold, analytical, bright, or not 'full bodied', I could not live with it.
Criticisms? People have said they work better with some speakers more than others, that they could use a 'good line conditioner', and they may have a flatter soundstage from front to back than tube amps. From my experience, I could not argue with any of these points. However, given my experience with amps the Rowland is still the best I have enjoyed.

Dcstep, How do you explain why neither the varnished Speltz Anti-Cable and my own virtually naked ribbon SCs have no hash issues? And why did the more lightly insulated Jenna sound less distorted than the Cardas?

Henry's amps are housed in a thick aluminum plate case. There is heavy internal shield separating the power supply from the module. My ICs are naked and long. My DAC and transport are obviously unaffected by any spurious ICE radiation.

Ghostrider, I do not mean to have my ribbons held up as a measure for the signal size. I just noted that it carries all frequencies with ease. The music signal is intensely complex. Timbre, dynamics, and musicality are a sum of an unimaginably complex wave particle pulse. I don't care how carefully a chip is designed to only cut out distortion, it is not going to be able to accomplish this task without taking out the most delicate of signal. Like I said, I can probe that here, and I have done so time after time.