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Experiencing Rowland M925 4-chassis reference amps

My pair (or should I call it my quartet?!) of the new SS Rowland M925 reference mono amps were finally delivered yesterday.... Needless to say, I am excited!

The 430W M925 monoblock amplifier is a hefty affair: The amp is formed by four chassis: two power supply chassis and two audio chassis, amounting to a total weight of 380 Lbs in the four boxes, and 320 Lbs in their birthday suits. Each chassis is double boxed, protected by heavy urethane foam inserts, and then bagged in a heavy cloth sleeve tied with a drawstring.

Each power supply box also contains an accessory carton, featuring a power cord terminated at one end with a 20A IEC connector, a heavy ombilical to carry DC current to the audio chassis, and a skinnier ombelical, which I conjecture carries control signals and may have an additional grounding line. A baggie contains 3 1-inch spherical delrin footers that can be screwed into the divets at the bottom of the SMPS chassis if if you do not use 3rd party spikes/footers. A smaller baggie contains 4 smaller delrin beads... They fit into the dimples milled into the top of each the power supply chassis, and are used to keep top and lower chassy from touching when the two are stacked.

I am using Nordost Titanium Sort Kones instead of factory-provided footers. Each power supply chassis stands on top of 3 divet-centered Kones. The whole thing sits on top of 1.5 inch thick granite slabs, which have been patiently waiting in place for the M925 amps since 2011.

The audio chassis are even heavier... They will get into place in the next few days, one way or another. Rowland recommends the stacking be a two-person job.

In order to break-in both output terminal in each unit, I will connect each amp to my Vienna Die Muzik with a form of shotgun wiring: Aural Symphonics Chrono and Cardas Golden Ref for the time being. The Aural Symphonics speaker wire connects to the single 5-way binding post of the Muzik speaker with bananas; the Cardas Golden Ref connects to the same posts with spades... I have already tested the configuration using other mono amps... Works flawlessly. Of course, I have no idea if M925s benefit from shotgun wiring... This will be part of the discovery fun!

The amps will be fed by the Criterion linestage through Aural Symphonics Chrono B2 XLR ICs.

Power cords will be Aural Symphonics Magic Gem and Ultra Cube XXV, plugged into a dedicated 20A circuit served by Furutech outlets.

According to Jeff Rowland, breaking may be excruciatingly long, because of the oversized input transformers and power supply. I suspect that the process may extend well into the summer months... I will log my periodic observations on this thread.

For sake of completion, here are the amps specs as far as I know them:

Monoblock Power Amplifier OUTPUT POWER: 430 watts @ 8 ohms/850 watts @ 4 ohms
Monoblock Power supply: 2400 W regulated DC SMPS per channel, with Active Power Factor Correction (PFC).
FREQUENCY RESPONSE: 5 Hz - 50 kHz
INPUT IMPEDANCE: 40k ohms
THD + NOISE: 0.004%, 20 Hz- 20 kHz
OVERALL GAIN: Switchable 26/32 dB
Combined AMPLIFIER chassis & POWER SUPPLY chassis WEIGHT: 160.4 lb / 73 kg (per channel)
TOTAL DIMENSIONS (H/W/D): 16.5" x 15.5" x 16.25" (per channel) 419mm x 394mm x 413mm

Saluti, Guido
guidocorona
krell888's avatar
krell888
12 posts
 
Morning Guido

The frequency response of the 825 is 5hz - 50kHz compared to the 725 which has significantly higher range (5Hz-350kHz). What this means to the music playback? Is 50kHz sufficient? If not the 725 may be a better pick.

The damping factor for the 625 comparing to most other class a/ab amps is relatively high except comparing with class d amps which have very high damping factor. Was told that a higher damping factor would be good to tone down speakers that are too bassy. But how much do u need actually. Maybe 200 is more than enough. Arc tube amps have damping factor less than 50! I noticed that Jeff does not specify the slew rate of his current models exept in the past. Don't know why as slew rate is an indication of fastness.

I m also concerned that class d technology for audiophile amplifiers is at its evolution stage while class a/ab amps are now at the peak and plateau. That means one could say that there will be better class d amps to come, whereas the 625 is already at its best in its class. Its difficult to accept that a class d amp in its evolution stage is already better than the class ab amp in its plateau stage of development.

I want to believe that 825 is a better choice than 725 but I m still struggling to leave the old school of thought that a/ab is the safer choice as the development is at its mature state,

Hope you can sway me more to accept 825. Please. 😄. Thanks

Bernard
guidocorona OP
4,298 posts
 
Excellent questions Bernard, let me try to address them…

• You are correct about the inherent sonic/musical limitations of old amplifiers based on the past generation of ICEpower modules. Without a lot of work from the amp designers, ICEpower ASP series modules invariably yielded sterility.
• NCore NC1200, and a few other new generation modules, are completely different creatures. In my own experience, even simple NCore NC1200 implementations, such as the Merrill Veritas that I have reviewed for PFO at
http://positive-feedback.com/Issue68/merrill_audio.htm
exhibit a degree of musicality and control of intermodulation distortion which is rare in amplifiers of any technology.
• I have listened to M825 at some length at RMAF 2014 over three days. I used my standard test CD that I have been using for all auditions during the last 7 or so years… Grand piano; string sextet with double bass; Diana Krall with her band; Symphonic; vocal ensamble + sax in a cathedral, Anne Sophie Mutter on violin with orchestra…. There was no audible trace of any harshness in the treble, which would have been the tell-tale sign of intermodulation sidebands. Neither multipart treble sostenutos of high strings, woodwinds, high brass, or fff transients showed any sign of ever breaking apart…. There was never any hardness nor shrillness, just exposed harmonic complexity.
• Compared to M925, I could not detect any M825 degradation of staging and images, which would have been the sign of cross-talk leaks.
• You are correct… If your Amati speakers are not bi-wirable, part of the benefit of adding a second M825 unit might be lessened.
• I have owned M625, M725, and M925… I comfortably prefer M925 over M725 for every conceivable audible parameter. Conversely, I found M725 to be somewhat closer to M625, although I still prefer M725 over M625.
• The difference in frequency response between M725 and M825/M925 has no bearing on any audible parameters of music reproduction…. The sonic/musical advantage goes to M825/M925 by a significant amount.
• Traditionally, amplifiers with very high damping factor have shown a propensity of generating hard cardboardy bass…. Not so NCore based amps… The bass resolution of M825 and 925 is controlled in the sense that it has no wooliness or pillowing, but it is deep, correctly fast, and filled with harmonics starting at the fundamental…. Do not be concerned about M825’s high damping factor.
• Class D designs do continue to evolve, and so do other class of operation…. However, while class A and A/B designs, with some exceptions, seem to be evolving relatively slowly, The underlying technology in some class D amplifiers have recently performed a quantum leap in inherent musical performance… Of course, to experience the absolute magic they are capable of, one needs to have the patience to go through a lengthy break-in process, as I have outlined earlier on this thread.

Bottomline.... M825 and M925 are phenomenal amps in the absolute sense... , Hope this helps... Let me know if you have more questions,
Guido
krell888's avatar
krell888
12 posts
 
Guido, you are simply the best. I am placing the order for that beefy 825. Will update about the sound some time later. Dealer here in Singapore told me, Jeff is struggling to meet demands as he personnaly checks every piece that goes out the factory. Waiting time could be awhile.
guidocorona OP
4,298 posts
 
That is fabulous Brnard... You will love M825... Do keep us posted!

Guido
krell888's avatar
krell888
12 posts
 
Hi Guido, did you ever wonder why, the heat dissipators or sinks of current amps are so huge? The size of the dissipators take almost half the width of the amp unlike the old amps like models 8 and 9 where the the dissipators are relatively smaller than the overall width of the amps. The fact that the m825 and m925 emit lesser heat because their output stage is Class D, they actually do not require dissipators as large as m625 or m725 in terms of the ration of the width of heat dissipators over the overall width. The reason I am asking this is was it because they want them to look beefy rather than functional?

Bernard
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