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
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
Hi Bernard, here are the reasons why the cooling blocks of M825 and M925 look the way they do....

* The semi-enclosed Venturi chimneys of these cooling units are more efficient than traditional blade designs in accellerating upwards air-flow and dissipating heat.

* The Venturi chimney design was first introduced in the M10 and M12 amps, and then re-introduced and finalized in the M625, with the prismatic faceplate first introduced in mid-production M312. Since M625, higher end Rowland amps have maintained the same consistent design.

* M825 generates more heat than you might imagine... Only NCore modules in M825 operate in class D, and by themselves generate more heat than old ICEpower modules used in old M3xx series... And there are two NCore modules inside M825. The rest of the circuit does generate larger amounts of heat than the power conversion modules, particularly in the power supply unit, where the SMPS and the PFC unit are quite massive... My music loft reacheas a normal temperature of 86F under air conditioning during summer months: in this season, the Venturi chimneys are a real blessing, because the unit becomes uniformly toasty to the touch... The uniform heat distribution ensures that internal components do not overheat, and so long term reliability is maximized.

* Of course, the total designs does contribute to pride of ownership... Doesn't it *grins!*

G
Thanks Guido. Btw, how is the sound of this Jeff reference compare to class A classics like Gryphon Antileon and the newer Gryphon Memphisto. I heard the Vitus and I am not for it. So are the Plinius which are also Class A design but does not sound as musical as the Jeff class AB design of M625. If there is any amp out there that can give Jeff's newest design a challenge, it must be the Gryphon as these are truly class A. If so, then one could say, class A design still rules the pantheon. If not, then Class D has finally arrive at the pantheon to replace Class A.
Sorry Bernard, the generalized class X versus class Y discussion is meaningless... In practice, no class is inherently superior to any other class... There are amps ranging from superb down to mediocre in every class... The only thing which matters is the individual design, and how its sound is in synergy with your particular taste in sound and in music.

The only SS brand in a similar price level as M825 and M925 that peaked my interest at RMAF 2013 was Solution.

Guido