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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 Tim, my amps are not gold color... Front and top are silver, while the side panels with their cooling vents are black.

As you know, I have become a fan of amps that are on the lighter side... So, currently, my only complaint is that M925 chassis are total bears to lift, particularly the audio units... On the other hand, I fully knew what I was getting into, so my gripe is pointless, sterile, and moot to boot *grins!*

Actually I live in Austin rather than in Houston.... Although,the State capital is not much cooler than its South Eastern neighbour. The good news is that I have heard that M925 may run comfortably cooler than M625 and M725, so I hope to be able to break them in throughout the summer months without turning my loft into a Sweedish sauna... We'll see!

Needless to say, I still remain intrigued to no end about the musical potential of new technology amps, including Veritas and Mola-Mola.

Saluti, Guido
french_fries
817 posts
 
This is so reminiscent of the introduction of the Model 9's so many years ago, with a choice of battery or A/C power supply boxes. The mere thought of having a pair of those huge amplifiers with the adjoining connections was enough to make most people (with the $35,000 in cash of course) wish they had a much bigger room to place them in. If i couldn't get my mind around what those might have sounded like in their last and best iteration, now i have an even greater disconnect with the sonic envelope the 925's can produce. And to have to wait for months for them to reach their full potential is just crazy- just put on the 1812 Overture for a couple of days straight! Just kidding of course, but i would hope they would sound quite good after a long weekend playing music "regardless" . At any rate, i am very happy for you and you should have a great time with them.
guidocorona OP
4,298 posts
 
Hi David, thankfully no batteries of any kind on M925s, nor is it likely there to be a batteries-based supply in their future... The only option for each power supply chassis is a 2400W regulated SMPS fed by a PFC-based rectifier.

Guido
french_fries
817 posts
 
forgive me for being so ill-informed, but i still don't know what power-factor-correction IS, and what the benefits of having it ARE. How does it differ from schemes used in past amplifiers to "purify" the incoming electrical source?
guidocorona OP
4,298 posts
 
Hi David, I do not pretend to be an expert on active PFC, so I am sending you to the Rowland Knowledge base for a few articles on the subject. Strictly speaking the articles deal with the PC-1 external rectifier... But its operating principles apply also to the internal PFC modules used in a number of Rowland amps driven by SMPS, including M625, M725, M825, and M925.

http://jeffrowlandgroup.com/kb/categories.php?categoryid=23

The interesting thing is that PFC rectification is compatible with external power conditioners, provided the conditioner is not power limiting.... I have used the now withdrawn Rowland M312 amp -- which is equipped with an internal PFC module, plugged into a Shunyata Triton, and results were marvellous.
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