Momentum Mono Blocks in Stereophile

[turntable]

Got my Stereophile today. Nice review and similar in respects to most of the other reviews. Does nothing in particular the best, rather the entire musical delivery is the best or one of the best regardless of price.

BTW - the front cover of the the Momentum is a Joke! Completely washed out with white balance over the top. My phone could take a better photo. Am I being to harsh?

Cheers

[PHC1]

Originally Posted by Erik Tracy

Interesting that in the "Manufacturer's Comments" section that there was no reply or explanation as to why one of the units overheated and turned off during JA's benchtests.

It sounds like one of the monoblocks may have developed a problem while the other one went on to complete the 1/3 power into 8 ohm load for an hour test on the bench.

That test really does stress the amps out which thermally is the worst case for an amplifier with a class-A/B output stage. Same thing happened to the McIntosh MC501 monoblocks when tested by Stereophile, they shut down after only 5 minutes!

In real world applications, neither my MC501 ever shut down or got hot nor my Momentum monos ever get any more than warm and that is being asked to drive speakers under movie soundtrack environment for hours on end with explosions, screeches, screams, bullets, bombs exploding everywhere, you know, all that stuff that makes the theater FUN! I saw the meters being pegged on those dynamic soundtracks so I had to turn the meter sensitivity down to the lowest setting! Barely warm.... Music? How about 8 hrs a day non stop while breaking in speakers and long session listening. Barely warm... Nothing to worry about at all.

[bdowell]

I know this is not a Mac forum but I had a Mac 501 shut down due it getting hot. That was during a party in the hot hot summer playing pink Floyd at stadium levels. The living room was in the upper 80 to lower 90 degrees. 5 minutes shut down it came back on. I look forward to seeing/hearing the momentums.

[PHC1]

Originally Posted by bdowell

I know this is not a Mac forum but I had a Mac 501 shut down due it getting hot. That was during a party in the hot hot summer playing pink Floyd at stadium levels. The living room was in the upper 80 to lower 90 degrees. 5 minutes shut down it came back on. I look forward to seeing/hearing the momentums.

Stadium levels may do it with the 501s depending on the load I guess. Never happened to me and I used to crank them while listening from other room. I don't do very well at 90 deg temps and my house is always at 68 in the summer...

I would not even attempt that but the Momentum monos are 2 ohm stable and put out 1200w! It is Dan D'Agostino, the KRELL man we are talking about here!

[jsli]

Originally Posted by PHC1

It sounds like one of the monoblocks may have developed a problem while the other one went on to complete the 1/3 power into 8 ohm load for an hour test on the bench.

Actually, no. Here's what was written:

"Unfortunately, after running at this level for 50 minutes, serial no. 0265 turned itself off with its heatsinks way too hot to keep my hand on. Those drop-dead gorgeous, lacquered-copper heatsinks may not, therefore, be as efficient at dissipating heat as more conventional finned heat sinks. I let the amplifier cool down, but it wouldn’t power up again, although neither the 7.5A fuse on the rear panel, nor the fuse under the bottom panel access plate, had blown. I therefore subjected the second sample, serial no. 0266 to a shorter preconditioning time, 30 minutes..."

[PHC1]

Originally Posted by jsli

Actually, no. Here's what was written:

"Unfortunately, after running at this level for 50 minutes, serial no. 0265 turned itself off with its heatsinks way too hot to keep my hand on. Those drop-dead gorgeous, lacquered-copper heatsinks may not, therefore, be as efficient at dissipating heat as more conventional finned heat sinks. I let the amplifier cool down, but it wouldn’t power up again, although neither the 7.5A fuse on the rear panel, nor the fuse under the bottom panel access plate, had blown. I therefore subjected the second sample, serial no. 0266 to a shorter preconditioning time, 30 minutes..."

Oh, ok so the test was shorter. It's all academic anyways, music and soundtracks do not behave the same way as stereophile's preconditioning test which thermally loads an amplifier to the max..

[jsli]

Originally Posted by PHC1

Oh, ok so the test was shorter. It's all academic anyways,

I respectfully disagree. There's nothing "academic" about inadequate heatsink design. It's not difficult to calculate the heatsink area needed based on dissipation required and materials chosen. Maybe the amp's designer wasn't aware how to make these calculations? Any properly designed amplifier should...should...be able to pass the industry-standard test Atkinson applied.

[PHC1]

Originally Posted by jsli

I respectfully disagree. There's nothing "academic" about inadequate heatsink design. It's not difficult to calculate the heatsink area needed based on dissipation required and materials chosen. Maybe the amp's designer wasn't aware how to make these calculations? Any properly designed amplifier should...should...be able to pass the industry-standard test Atkinson applied.

I assure you Dan D'Agostino knows what he is doing. I doubt he was designing the amp to pass "industry-standard" Atkinson test.... Like I mentioned before, my Momentum monoblocks are HAMMERED in the home theater environment where movie soundtracks shake the room and the rest of the house.... Often followed by another 5 hrs of music.... Just warm to the touch... YAWN... The copper heatsinks with venturi design are A LOT more attractive than the typical fins... I've had enough of those razor sharp fins, the Momentum monos are a refreshing design that is pleasing to my eye.

[jsli]

Originally Posted by PHC1

I assure you Dan D'Agostino knows what he is doing. I doubt he was designing the amp to pass "industry-standard" Atkinson test.... Like I mentioned before, my Momentum monoblocks are HAMMERED in the home theater environment where movie soundtracks shake the room and the rest of the house.... Often followed by another 5 hrs of music.... Just warm to the touch... YAWN... The copper heatsinks with venturi design are A LOT more attractive than the typical fins... I've had enough of those razor sharp fins, the Momentum monos are a refreshing design that is pleasing to my eye.

You seem to be confusing the facts with your likes and opinions. Obviously the copper material and venturi design are, in and of themselves, fine. The designer needed more of both, however, for proper dissipation. The test in question isn't Atkinson's--it's a standard of which every competent designer is aware, your assurances notwithstanding.

It's heartening to hear that the amp works with your speaker load. Someone with less sensitive speakers may not have such good fortune.

[PHC1]

Originally Posted by jsli

You seem to be confusing the facts with your likes and opinions. Obviously the copper material and venturi design are, in and of themselves, fine. The designer needed more of both, however, for proper dissipation. The test in question isn't Atkinson's--it's a standard of which every competent designer is aware, your assurances notwithstanding.

It's heartening to hear that the amp works with your speaker load. Someone with less sensitive speakers may not have such good fortune.

Facts? You have facts??? Are you an engineer? You would have done it differently with your applied experience and knowledge?

Look, I don't know what your agenda for your post is but it is becoming evident... What I am saying and I don't care to make a lengthy debate out of this as we are a friendly audio forum, not like others, is that Atkinson test and real world applications are far, far apart. There have been plenty of other amplifiers that have failed the test. The McIntosh MC501 and MC1201 both shut down from a thermal overload, 5 min and 40 min. Other amplifiers were so hot that they would burn your hand if touched, DarTZeel for example, others failed from rated output testing like Ayre MX-Rs... Pass Labs amp failed as well... These are all respectable brand names! These amplifiers have no problems operating reliably in numerous homes with all kinds of speakers.

Besides, before accusing someone like Dan D'Agostino who has been in the audio industry and has designed as many products as he has in the past 33 years of poor engineering practices, get to the bottom of the situation first.

Here is Dan D'Agostino's response from elsewhere on the net where this was brought up...

"I am sorry that you interpret this as a melt down. The Momentum amplifiers normal operating temperature is 42-44c(107-111f)the temperature rise to 48c (118f) is inconsequential. The amplifier in question failed from a non related component failure in the power on circuit.The Momentum amplifier is designed to shut down at 70c (158f). The unit under test was not close to that temperature.Many amplifiers at higher temperatures than that.If John had continued his test the second amplifier would have passed witout any problems. The Momentum amplifier has more than enough thermal head room for any load or speaker. I was unable to give comment until the unit was returned to me from testing. Thank you for your concern.
Dan D'Agostino "