Same watts at 8 and 4 ohms?

Building amps with huge power output is one of Dan D'Agostino's top priorities.  They are all advertised as doubling down into 4 and 2ohms.

Here is what Stereophile measured in its review of the Momentum Monoblocks:

Specified as having a maximum power of 300W (24.8dBW), the Momentum comfortably exceeded that rating, clipping at 405W into 8 ohms (26.1dBW), with clipping defined as the point when the percentage of THD+noise in its output reaches 1% (fig.5). Fig.6 reveals that the amplifier clips at 640W into 4 ohms (25.05dBW), while into 2 ohms (fig.7), the amplifier puts out 1115W (24.45dBW). As with Dan D'Agostino's earlier amplifier designs for Krell, the Momentum is a powerhouse!

https://www.stereophile.com/content/dan-dagostino-momentum-monoblock-power-amplifier-measurements

Like I said, impossible to exactly double. And understating the 8ohm wattage figure

But these are better "close to doubling" figures down to 2ohms than any Class-D’s or even linear Mosfets with complimentary push pull output stages can achieve.

The Momentum comfortably exceeded that rating, clipping at
405W into 8 ohms
640W into 4 ohms
1115W into 2ohms

And yes Dan D’Agostino’s Krells, and the Momentum’s are powerhouses, that others claiming to be and can’t should try to mimic.

Cheers George

This is the false statement, and is the typical statement of amp manufacturers that can’t double down with their amps.

This statement is false.

I recently serviced out a Realistic receiver with 18 watts. Even though it has no chance of doubling its power at full power, at power levels less than full output, it does so with ease, for the simple reason that despite its inadequate supplies and heatsinks, the amp behaves as a voltage source. Its only that last 3dB into half the impedance that is being touted as such a great thing- and really has very little effect if any on how the amp actually sounds.


Any conversation otherwise really points to not understanding how a voltage source works, and why its important. Now its been pointed out that no amp can really double its power at full output when the load is halved. This is true because of a thing called Ohm's Law. It has to do with the output impedance of the amplifier being finitely more than zero. Whatever that value is, it will always prevent the voltage amp from perfectly doubling power as the load impedance is halved ***at full power***.


Since actually doubling power at full power can't be done, how important is it? If sound quality is your goal, its likely that the amplifier topology will play a bigger factor in the sound of the amp,  on account of how it makes distortion, and how audible that distortion is, especially at lower power levels where the amp spends most of its time with real music signals. Its also unimportant because you can't operate the amp constantly at or near full power due to the dynamic nature of music. 

I bought my big krell amp because my apogee duetta 2 speakers are very inefficient at 80db/w. 

The big Krell current wattage doubling grunt is not really fully utilized here, great sounding amp still with these speakers just a bit of overkill.

Apogee Duetta 2 is one speaker that doesn’t need so much an amp that can "nearly" double all the way down to 2ohms from 8 and 4 ohms.
Because it’s load impedance is very benign lowest at 5ohms,
https://www.stereophile.com/images/archivesart/Duetfig1.jpg

But as you say it’s efficiency is only 80db and this just needs lots of watts, even high wattage Class-D and or linear Mosfet poweramps will suffice into these speakers.

Cheers George