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Dont get me wrong, I love my A21. But compared to my old Rotel 1080, it is huge. Is the size difference due to the 50W per channel increase in power? Is it because the A21 uses the same chasis as the more powerful A51 and JC1 amps? Just curious why its so big.
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One reason is because the max power is rated as MAX CONTINUOUS power. If you really punish your A21 and drive it at near full power with a steady sine wave, then those big heat sinks will actually be used.Originally posted by tboooe
Maybe Rotel does not promise continuous delivery of the max power in their specs?!
That's also the big difference between Halo and Classic. The classic amps don't promise continuous power at the max rating.
Peter -
Uuuuuuh.... The specs only say 2x200 watts?!?!?! WHAT?!
The A21 is 2x450W in 4 ohms. That's almost (but only almost) twice the power as in 8 ohms.
As they all say, the quality of an amp's power supply can be verified by the fact that the power should double in 4 ohms. Does the RB-1080 output 2x400 watts in 4 ohms? The on-line specs don't reveal that, which makes me believe that the power supply gives up a lot sooner. Not a biggie if you have highly resistive 8 ohm speakers, but for all us owners of 4 ohm speakers it is a matter of go or no-go.
PeterComment
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Pete, your passion and confidence in the A21 makes me smile.Comment
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peter, so are you saying that it is unclear whether or not the Rotel 1080 puts out 200 x 2 continuous?Comment
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There have been several reviews/test done on the Rotel RB-1080, here are a couple:
Australian Hi-Fi test Laboratories:
Rotel RB-1080
282 watts @ 8ohms
479 watts @ 4ohms
800 watts @ 2ohms
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Stereophile:
291 watt @ 8ohms
558 watt @ 4ohms
800 watt @ 2ohms
Remember, Rotel is well known for "underrating" their products and not pushing the specs like some manufacturers. :TComment
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continuous or peak ratings?
Brent Huskins
Media Design
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The same goes for Parasound. (Look at the Stereophile JC-1 review, for instance).Originally posted by ProStereo
However, as with their JC-1 review, those figures are peak powers. (The amp was not run 24/7 with those loads).
The original question was why the A21 is so big. It is because it can deliver 2x450W continuously, 24/7/365, in 4 ohms.
PeterComment
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Those are "continuous" ratings.
Stereophile said: The Rotel RB-1080 - Considering it's modest price, this is one powerhouse of an amplifier.Comment
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I think that the A21 is the size it is just to be on the same chasis as the A51. I've been inside both the 1080 and the A21 and while less densly packed, doesn't have anything that would require the extra space. Theoretically at least it should run cooler than the 1080, with all the extra heat syncs, which it does. The 1080 runs quite warm.Jerry RappaportComment
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The quotes you use around continuous is exactly what makes the difference.Originally posted by ProStereo
I don't doubt that they did push out that power out of the RB-1080 for 24 hours continuously. However, if they did, then they must have had a big fan blowing cool air on the RB-1080, or alternatively, they had a low ambient temperature testing room (say 50 degrees).
I'm NOT questioning Rotels ability to push out that power! I'm questioning the amps ability to dissipate the generated heat at max power without forced cooling in high ambient environments (75-80 degrees).
The advantage of the big heatsinks of the A21 is that it should be capable of pushing out full power, continuously, WITHOUT needing fans or additional cooling in a 75 degree room.
PeterComment
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PeterOriginally posted by Peter Nielsen
How often do you think that may happen in the average home theater? I'm sure Babe Ruth could hit home runs with a diamond studded bat as well as he could with a plain wood one.Jerry RappaportComment
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Strange, the Rotel RB-1090 runs darn cool, even when pushing it hard.
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You're right. In real life, the max power will very seldomly be used, and especially not for longer periods of time...Originally posted by DrJRapp
Still, the big heat sinks are needed on the A21 to sustain the high idle bias current. I guess this is a much more valid reason.
PeterComment
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Strange, I run my RB-1080 hard for quite long periods and it barely gets warm. I have an AC fan mounted in my amp's cabinet (installed for a previous amp) but I never need to turn it on.Comment
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I think what is installed inside make sense for its size. What really caught me off guard is what is inside a MF A5 intergraded amp. Check it out. http://www.walrus.co.uk/musfid/musfid.htm
JayComment
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