Rowland M625 class A/B 300W Stereo Stereo Power Amplifier

GuidoCorona · Dec 31, 2010

The Rowland Model 625 Stereo amplifier started to ship in December 2010.

M625 is a single chassis class A/B design; Power rating is 300W at 8 Ohms, 550W at 4 Ohms; Input impedance 10K Ohms; damping factor: 200. maximum current ratings have not yet been published. M625 is fully balanced in the input and output stages. As far as I know, both input stages and output stages are transformer coupled, probably using Lundahl transformers. The power conversion stage uses no global feedback. The bias adjusts itself upward as the unit warms up, moving more toward class A. The most interesting bit on the M625 page asserts that M625 "Features a unique composite circuit architecture incorporating separate Class AB voltage and current gain blocks with no overall negative feedback." The amp uses a high speed SMPS prefixed by a PFC-based rectifier, instead of a toroidal supply. As typical for Rowland devices, the silver-only chassis is milled from an Aluminum block by Vertek in Colorado Springs. The heat sinks are massive and work extremely well to regulate and dissipate heat: whenever I touched M625 in Denver, temperature appeared to be identical all over the chassis.

In Denver at RMAF, the evening of Friday October 15th, a brand new M625 amp replaced a pair of very well broken in Rowland M301 monoblocks in the Rowland suite, and was used until the end of the show. It was my distinct impression that M625 immediately exceeded the performance of M301, and continued to sweeten and open up until Sunday afternoon. I have not heard a well broken in M625 yet, nor have auditioned one in my own system, so I will leave it to actual owners to comment on its sound in detail.... Yet, the little I heard was already momentous.

The product section of the new Rowland site has photos, features and specs, including the metalwork done by Vertek at:

http://jeffrowland.com/websitepublisher/amplifiers-model-625.html

The complete M625 Owner's Manual can be downloaded at:
http://jeffrowlandgroup.com/kb/getattachment.php?data=NDc5fEpSREdfTTYyNV9NQU5VQUxfUkVWQjEtMS5wZGY=

US price: $14,500.

Husk · Jan 7, 2011

Guido, Don't you have pretty efficient speakers? I am wondering why you would need the 925 as opposes to the 625?

GuidoCorona · Jan 8, 2011

Hi Husk, you mean.... except for.... uncontrollable audiophilic greed?!

I am actually planning to compare the performance of M312, M625, and eventually M925 in my own system, and determine what works best in my listening room. My current hypothesis is that M625 might exceed M312 in musicality, image solidity, and resolution, while M312 might yield a slightly bigger stage. In turn, M925 might exceed stage size of M312, and--apparently being an even more sophisticated design--might be even more resolving and musical..... Of course, this is only theory by my feverishly audiophilic mind.

The Vienna Mahlers are actually somewhat power hungry.... Their 91dB efficiency is deceptive.... It is countered by a bit of a wilding impedance curve that requires lots of power, lest the proverbial flabs set in to destroy the magic. Lastly, there is the possibility that I might upgrade my Mahler V1.5 speakers to Vienna Die Muzik.... I sure would like to compare the performance of these three amps on the Muziks.

Saluti, Guido

Husk · Jan 8, 2011

Guido, Great response. I am just trying to figure if the 625 would make my Q5's sing or do I need to step up to the 925. Any thoughts on that?

GuidoCorona · Jan 8, 2011

Husk, as M925 power ratings have not been released yet, it's a little difficult to guess an answer accurately.... To start with, here are a couple of questions for you:

What is your current amp and what is its power rating?
What does it do well on Magico Q5, and where might it need improvement?
What are the power requirements and impedance behavior of Q5?

Guido

Husk · Jan 8, 2011

Guido, I am concerned about the heat from even the 625 let alone a pair of 925's. A friend of mine heard the 625 at CES and said he could not put his hand on it for more than 5 to 10 seconds. Seems like a pair of monoblocks would really heat up a room.

GuidoCorona · Jan 9, 2011

Husk, valid concerns... over 3 days of repeated listening at RMAF, I would characterize the external temperature of M625 to have range from 'warm' to 'toasty', but definitely short of uncomfortably hot. Of necessity, one of the variables in a device's temperature is the external thermal environment: if indeed at CES the JRDG components were artfully illuminated with a number of spotlights, the room temperature would have been higher, and so would have been M625's skin temperature. Yet, for sure, M625 does not run as cool as M312 or M301.... perhaps more like the Continuum 500, which is apparently toasty to the touch.

Perhaps David Goodman (Kawika) can report on his M625 temperature findings on this thread, or on 'that other' audiophilic watering hole. A home test is more valid than any occasional showfloor fondling.

G.

kawika · Jan 10, 2011

Guido and Husk, I haven't put a thermometer on the chassis of the 625, but it seems to be ever so slightly cooler than that of the 625 we heard and felt at RMAF last October. I can hold my hand on it for a long period without any pain. Uncomfortable..Yes. As for the sound-stage size compared to the 312...It's bigger, but not by bloating images. It is bigger from low level ambient info that hangs longer and is much much more evident than the 312 could reproduce. The 312 just didn't have the ability to do what this 625 does. Jeff's circuit in the 625 gives so much of the 3D magic of tubes but without ANY of the negatives that tube circuits present. Power wise, I think a 625 is adequate for most people, but those of us who have had big powerful amps in the past and believe Jeff can take this new magic that the 625 has and expand it into an seemingly unlimited power source, will want it badly! I'm one of these sort of people

kawika · Jan 15, 2011

A few days later...............After over an hour running at and probably over 200 watts with highly dynamic source music the amp is now too hot to hold my hand on it longer than 5-7 seconds! Hopefully this won't affect the long term reliability and performance of the amp. Even if it does, it's worth the trade off in its performance over the ice module powered amps that preceded this one!

rhyno · Jan 16, 2011

hey david., thanks for that nugget. ---for us here in the deep south, that kinda heat output is a deal breaker on some amps (at least it is for me). ---damn shame folks cannot make an amp that sounds like class A tubes without the heat.

i do suspect the higher heat output will influence reliability; heat always does that. but are we talking 10 yrs instead of 15, then who cares?

GuidoCorona · Jan 16, 2011

Rhyno, one factor in the heat signature of M625 is the automatic self biasing of the device. For what I understand, as the average throughput rises, biasing moves more towards class A. On the other hand, idling power appears to be much lower, indicating that the biasing may readjust downward as well.

One more factor is the high compactness and circuit density of the device, hence the relatively higher heat dissipation per square inch. If the device were larger, skin temprature would be deceptively lower.... 100W idle consumption per the specs at:
http://jeffrowland.com/knowledgemanager/questions.php?questionid=585

Concerning long term reliability, we can hope that M625's behavior is similar to older high bias JRDG designs.... Anecdotally speaking, as far as I know, my former JRDG 7M monos are still making music without issues over 20 years since they left the factory.

Rhyno, do you live in Houston? ... So does David (Kawika). G

Husk · Jan 16, 2011

Kawika, I am not especially concerned with how hot the 625 is to the touch, but how much ambient heat it puts off in your room. What is like in your room after a few hours of listening? Do you leave it on 24 x 7?

Husk · Feb 8, 2011

GUIDO, I am hearing that the 925's are 4 to 8 months out. Not good news.

GuidoCorona · Feb 8, 2011

Husk, that is quite possible.... M925 may end up much more complex a project than a higher powered port of M625. in the meantime, I am considering an M625 to tie me over. I have reports that M625 was handling the Vienna Die Muzik at CES with very high synergy. G.

Husk · Feb 12, 2011

Guido, You are probably right. Jeff never releases anything until it is perfect. I believe they are also spending a lot of time and energy on their new dac.

Orb · Dec 21, 2011

Guido,
appreciate it may had been awhile since you listened to the M625, but can you remember how hot in terms of temperature the amp operates; did it seem warm-hot-etc?
Curious as it seems to have low mains consumption when idle (some kind sliding bias I assume), so wondering if this reflects lower operating temperature when idle, and also when it is in use.

Cheers
Orb

GuidoCorona · Dec 21, 2011

Hi Orb, yes M625 appears to have an automatic bias adjustment. As far as I know, it idles at approx 100W. During operations, the bias grows as needed. Skin temperature of the device seems identical on top/sides/front/back, and also depends on room temperature... Seems to range from medium warm to rather toasty, depending on duty cycle and room temperature.... Only during August, when my music loft sometimes reaches the mid/high 80s, M625 may become borderline too toasty to touch.

Orb · Dec 21, 2011

Good to know, thanks

Cheers
Orb

GuidoCorona · Dec 23, 2011

I called the JRDG factory today. The M725 monos have just been released and have started to ship. Price seems set at $28K for the pair. Production level units will be heard at CES in January. G.

GuidoCorona · Jan 19, 2013

Hey Husk, in case you were still interested, JRDG has just release the Model 925... Yes, the charming quad-chassis monoblock amp is shipping. I have just posted updated specs for M925 at:

http://www.whatsbestforum.com/showthread.php?2034-Rowland-925-amp

Rowland M625 class A/B 300W Stereo Stereo Power Amplifier

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