All, looks like I am a little late to this Rowland/VAC watering hole... Here are some clarifications about M625 S2 and Aeris DAC....
1. The M625 series operates in higher bias class A/B. It does not run in class D, as someone seems to hav suggested instead.
The current version of M625 is M625 S2. This model delivers 325W / 8 Ohms instead of the 300 of the original. Internally, it has several enhancements over the original and its sound considerably more refined. A while ago I received some details from the factory:
...
The 625 S2 improves upon the original 625 in a number of important areas.
We have taken the existing circuit topology and improved the important distortion specification at higher frequencies (above 2kHz) to a virtually unmeasureable level extending beyond 20 kHz .
This was accomplished with an innovative error correction technique previously unknown, or never implemented in the art of amplifier design.
The S2 incorporates a new custom designed input transformer and linear phase low pass filter for improved input signal buffering and EMI immunity.
Gold plated Cardas XLR input connectors with Rhodium contacts and teflon insulation provides a visually distinguishing appearance from the original 625 and provides improved signal integrity.
The S2 amplifier incorporates ceramic Rogers circuit board material for reduced dielectric energy storage.
The S2 Power Factor Corrected regulated Power supply improves upon the original 625 by incorporating Jensen four-pole capacitors which offers nearly an order of magnitude
reduction of output impedance and noise suppression. The power supply output voltage has been increased slightly to yield a 25 watt increase in total amplifier power output.
...
I have received the M625 S2 manual complete with technical specs. Here is a link to it on my public DropBox.
https://dl.dropboxusercontent.com/u/53640097/JRDG_M625_S2_MANUAL_REVA1.pdf
And here is a link to the January 2016 review article on HiFi News:
https://dl.dropboxusercontent.com/u/53640097/HFN_Jeff%20Rowlad%20625%20S2_hires.pdf
All Rowland amps can be driven successfully from the Aeris DAC without a preamp in between... I drive my own Aeris directly into my M925 monos. If you use a preamp between Aeris and amp, you should set the Aeris attenuation to the DAC's equivalent of unity gain: per the Aeris manual, the right volume LED is lit up solid without flashing.
I have used Aeris on its own as well as with the Rowland Criterion linestage. Criterion is the now discontinued battery-powered version of Corus. With Criterion between amp and DAC the presentation is slightly softer/warmer, while driving Aeris into amps directly, resolution and transparency is maximized and background noise essentially non existent.
It is worth pointing out that Aeris as well as Rowland amps take a very long time to break in completely.... Complete stability is achieved at approximately the 1500 hours mark. Particularly, evaluating such electronics with less than 800 hours on them will yield false results... Aeris for example may still sound subtly peaky in the treble... Yet, there is nothing peaky in a fully stabilized Aeris... Sound is extremely complex and rich, without emphasis on any particular band of the spectrum.
As for Rowland delivering magic... Yes, Aeris + my M925 monos do deliver extreme magic to my ears. It is my conjecture that the combination of Aeris with M625 S2 would be as satisfying, while not attaining the same enormous scale of power-dependent parameters. Eventually, I hope to be able to verify this hypothesis in my own system.
BTW, there is now M725 in production.... Essentially same circuitry of M625 S2, but in monoblock configuration. 330W/8 with 1200W DC SMPS and dedicated PFC unit in each chassis.
Let me know if you need further information.
Regards, Guido
