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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
guidocorona OP
4,298 posts
 
Hi Psag, I appreciate your misgivings. I heard M201 monos a few times... Driving Maggie 1.6, Maggie 3.6, Vienna Mahler, Vienna Beethoven Grands... In all cases, M201s ran out of steam at the first indication of dynamic excitement... When they did not run out of steam, the sound was clean, sweet, and transparent, but not highly emotionally involving.

M201 were not representing the state of the art in class D amplification at the time of their release. They were based on mid-power ICEpower 500ASP modules, and were implemented as an entry level product. They had neither the power to drive demanding speakers like M501s, nor the power supply / PFC refinements of all the old M3xx series.

By extension, they are not indicative of the behavior of any current products, from M525 upwards.

G
psag
518 posts
 
Hi Guido, I had them driving a benign load (Vandersteen 5a) in a smallish room. At 250 wpc, they certainly had ample power to drive the Vandersteens to extinction if need be. I was never aware of them clipping or running out of steam. The consensus is that the 501's sound identical with a benign load. Also, its safe to say that Jeff Rowland would never put out a product if he didn't believe in it. But I have no doubt your amps are the more evolved and refined product.
guidocorona OP
4,298 posts
 
Yes PSAG, you are correct... I compared M201 and M501 in the same systems a couple of times... M501 have a sonic signature very similar to M201.... With more grunt, dynamics, stage/imaging size, but no greater microdynamics, harmonic content or treble detail. M3xx series are different creatures instead... But if you feed M201 through a PC-1 PFC rectifier box, you should obtain a good portion of the audible refinements of the M312.

G.
guidocorona OP
4,298 posts
 
All, I have received the list of RMAF suites where we will be able to listen to Rowland amps coming Friday through Sunday:

The M825 stereo amp, Aeris DAC, and the Capri Series 2 preamp will be playing in suite 8032 with Joseph Audio speakers and Cardas Clear wires.

M825 and Aeris will also be heard with Lawrence Audio in Tower Room 1122.

The Continuum S2 integrated will be making music in public for the first time in Tower 2001 (the Rowland suite), together with AerisÂ… If I remember things correctly, they may be using Cardas Clear and Clear Beyond wires, and Raidho speakers.

Other Rowland products will be mostly on static display in room 2000 and 2001: including M925 monos, M725 monos, M625 stereo, M525 bridgeable, Corus linestage, and Capri S2 pre.

Saluti, Guido
guidocorona OP
4,298 posts
 
Fredmiu and all, apologies for my oblique posts last week.... A couple of days ago, JRDG has finally posted a partial list of M925 and M825 technical features and specifications... Bottomline is that yes, you are correct. In the output phase of these amps there is a circuit running in class D... based on the fabulous Ncore NC1200 technology to be more specific.

http://jeffrowlandgroup.com/kb/categories.php?categoryid=212
http://jeffrowlandgroup.com/kb/categories.php?categoryid=213

Note that The amps do not utilize the small companion Ncore SMPS made by Hypex... Power management is designed by Rowland specifically for these amps... a PFC rectifier feeds high voltage DC into a large 2500W SMPs... Seems that the resulting low voltage DC is then cleaned up further by 4-pole capacitors. Signal imputs are transformer-coupled with large Lundahl transformers... There is a little bit more info on the links above, but not quite as much, or as clear as I would like to see.

I will try to gather more details from Jeff, Lucien, and Brandon while I am at RMAF.

Saluti, Guido
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