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Heat from amps?

Looking through the forum threads on amplifiers I’ve read posts stating how the Pass Labs x250.8 gets warm enough for the occupants in the room to take notice, along with comments of being thankful for having an air conditioned room. In degrees, how much are we talking about at what levels of volume? I’d like to take all things into consideration while comparing power amplifiers. I have not been playing my Bryston 4B3 demo at loud volumes for long periods of time, but, as of yet, and the heat sinks have only gotten warm to the touch.

update : Keith English at Pass Labs had me call the dealer who I,ports Harbeth. "The 250.8 is too powerful, the XA25.8 is what we recommend." When asked about the XA30.8 I was told there is little difference compared to the XA25.8," and they reiterated the recommendation of the XA25.8 which has more than capable for handling my Harbeth 30.2 XDs. I thought dealers like to up sell? I'm worried about the handling of the bass on the XA25.8.
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daveyf's avatar
daveyf
2,875 posts
 
Amp heating the room seems to have a great deal to do with how large the room size is and how hot the amps run. Tube amps generally seem to run hotter than ss. However, another variable is how much heat radiates off the amp. I have a large ss amp that has a lot of radiating surface, so while the amp doesn't get too hot to the touch, the amp's large radiating surface lets off enough heat in my very small room that the room heats up considerably after just a few hours. With tube amps, IME the number and type of tubes effect heat propagation..the more power tubes will usually mean more heat. I always laugh at tube amp manufacturer's who are selling their 'flagship' product that features 10-30 power tubes, all biased hot, that are selling these products in warmer climes. Poor buyer better have great AC and a huge room to accommodate them....plus he better get used to listening in his underwear, ha! 
voodoochillin's avatar
voodoochillin
61 posts
 
Aside from the heat consideration, you must keep in mind that the XA25 and X250.8 are different in their design (single ended vs. balanced) and will have considerable differences in their sound. I seriously doubt that the 250.8 would be "too powerful" for your Harbeths at 85 dB sensitivity. Regarding the sonic differences, I have been told by the folks at Pass that the 250.8 is more extended on the top and bottom end but doesn't quite achieve the rich midrange that the XA25 delivers. 
cakyol's avatar
cakyol
940 posts
 
@g_nakamoto

The heat generation of an amp does not have as much relevance to its design but much more to the "class" of amplifier it is.

Class A amps are biased almost at the center of the operating range of its output transistors and hence generate a huge amount of heat.  It is deliberate by design.  Some optimizations and workarounds exist but that is generally the case with class A amps.  Unfortunately, those are also the ones that sound the absolute best (in general) in terms of sound quality.

Class B (and A/B) generate much less heat.  The more A bias a class A/B is, the warmer it will get however.

Class D are the most efficient amp designs and run almost with 90/95% efficiencies.

These numbers above are typical, some exceptions and design variations do exist however.

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