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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
4,114 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
735 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
4,114 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.
guidocorona OP
4,114 posts
 
This afternoon the M925s yielded "first sound". Even more than encouraging, it was a bit of an OMG experience.

I managed to connect M925 without breaking anything and without shorts...
I was expecting the usual shrieky time, but... M925 is so musically revealing after 30 minutes of playing that it is spooky... By the way, this has been the First time that my better half has made unbidden positive comments on a component right out of the box... Less than 10 minutes into playing time actually.

WhatÂ’s astonishing is that, factoring in very minor early oddities, M925 already convey a grandness, poetry, and realism that I have never heard from my own system.

I fully expect for musical beauty and detail to wax and wain for quite a spell, but for the time being, the cadenza in the introduction to the Dvorak string sextet with double bass Op. 48, is almost free of artifacts, which is something I have not yet experienced with a brand new amp.

Likewise, my other test piece by Antonin Dvorak "In the Old Castle", played by Inna Poroscina on what is likely a Bosendorfer Imperial grand, is already showing signs of pedal and felt sounds, which is quite unusual on a brand new amp.

But perhaps the most encouraging sign is that I felt just like sinking into my couch and immerse myself into the music... Will this last? We will see as the break-in enfolds!

G.
guidocorona OP
4,114 posts
 
At 20 hours, the stage has a nice depth to it.... In addition, resolution is intriguing. Yes, I am discovering some of my CDs anew... if sometimes in unusual ways: I have a set of Bach Well Tempered Klavier played on harpsichord; and I had never realized that there some cute errors in the performance... Not wrong notes per se, but errors in timing between the two hands, and some rhythmic imperfections. Until M925, such minutiae were blended into the background.

I had a little "excitement" yesterday: I had a friend over to help me with the chassis stacking operation... Yes, it is a breeze with two people. However, when I powered up the right amp, the right speaker started to emit a bizarre multi-frequency burr, as if I had a mad cicada in rut inside the coaxial flat driver... And no music signal could be heard at all from that side... Disconnected and reconnected the whole amp to no avail.... The factory assured me that I must have done something wrong with my connections. True enough: I eventually discovered that the source selector switch was inadvertently flipped upward to RCA mode. Flipped the switch back to XLR balanced and reconnected... The amp started to work again without further ado.

But with hour 21, the amps have decided it is high time to go into a bit of break-in funk. Image is more recessed and has lost some airiness. The voice of Mezzo-soprano D'Althan in Exulta Filia by Claudio Monteverdy has developed a bit of a steely burr on the sostenuti at end of phrases, where the incompetent recording engineer is fooling around with artificial reverb to enhance the echo of the small church used as recording venue.

Now I have inserted a tuner into the system, so to exercise the amps 24/7... Nighttime the amps will be served a diet of FM interstation hash.... Extremely healthy and highly decongesting!

G.
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