The X250.8 is a class AB amp with a fair amount of bias current. The idle power dissipation is 450w. With higher efficiency speakers, you probably will be in class A bias most of the time, so power dissipation isn't going to be that much higher than the idle dissipation.
However, your Harbeth speakers are not that efficient at 85db/w. I'm surprised the dealer felt that a 25w or 30w amp (rated power) would be the best match.
Both the XA25 and XA30.8 are class A amps with high bias. The XA30.8 idle power dissipation is 400w, almost the same as the X250.8. But as long as you are staying in class A bias, it's power dissipation will not go up while playing music (in fact, it will go down a bit). The XA25 has lower bias current and idles at 240w. The XA30.8 has higher peak power in class AB than the XA25, but I doubt that you will notice that much difference between the two. One other difference is that the XA30.8 supports balanced inputs, while the XA25 does not.
It's impossible to say how much your room temperature will increase with these amps since it depends on the size of the room, insulation, other heat sources, outside temperature, etc. I have a pair of XA60.8 monoblocks, each of which idle at 425w. I haven't owned them during the hottest months of the year, but so far, I haven't noticed that my room is any warmer (without AC being on). But my room is fairly large at 29' x 17' x 8'. |
The Pass 250.8 is not heat like a tube amp I had a Pass 350.8 I did not think it ran overly hot.However its up to you that amp sounds wonderful with great dynamics and bass control. |
I had Pass X600 mono blocks. Those are like running a space heater. 600 watt draw at idle each. Much more heat than my Audio Research VT-100 Mk II. |
some dealers have scruples... want the customer to buy the right thing
i will bet its reno hifi.. they are honest and knowledgeable... excellent |
You want hot? Try an old krell pure class A amp. Pass runs cold next to those. Pass class A/B do not run hot but warm. You’ll be fine with a 250.8. |
i would think that any well designed amp would'nt have a heat issue!!
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I have a coda amp ,integrated and you have get 3 choices of power and first watts from 5, 18 and doubles watts down from 8-2 ohms
with highest amperage largest potted transformer then Anything in its price class and above 3kva , a true great piece of engineering and bargain. |
I have the Pass XA25 and while it gets warm to the touch it does not radiate heat like a tube amp. The XA 25 is a very special amp once you reach 200 hrs. |
You'll get warmer than "occupants" when you see your electric bill. |
As jaytor pointed out you need to know how many watts the amp draws at idle. An amp that draws 450 watts at idle will put out the same amount of heat as 4 100 watt light bulbs and one 50 watter while idling.
Class D amps put out the least amount of heat, then Class A/B amps which switch over to Class B at low watts, say one watt. The more watts the amp puts out before switching to Class B the more heat it will produce. Some A/B amps switch at 10 watts, some 25, etc. Class A amps run at full power all the time and most of the electricity they use is turned into heat. A 25 or 30 watt Class A amp will not cause heat problems for most people, though. Finally, if you really want some heat, get a tube amp. This is an overly simplified explanation, but maybe it will be some help. |
Kinda shocked to hear people say that they have multiple amps idling at 400+ watts and they didn’t notice the temperature change. My Pass X5 idles around 200w and I can notice the room temp change within thirty minutes.
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I had a Pass x350 for fifteen years and it never got more than warm to the touch. |
I had a Pass x350 for fifteen years and it never got more than warm to the touch. |
I have Aleph 1.2 monos and they’re on almost all day, hot to touch and idle at 300w, but I feel no room temp change and I live LA. |
Class A sugden gets pretty hot, however I am not concerned about it altering the temperature of a room. I have not noticed one bit if difference in comfort. You want good sound then you accept a bit of heat, that's class A. |
Pass 250.8 does get warm, no doubt, but I would never call it HOT...to me, hot means you couldnt touch it without burning yourself....incandescent lightbulbs get hot....both of these items indeed radiate heat, own them all, but have never found they make a room "uncomfortable", and I live in Florida....owning the 250.8, I have never seen it leave Class A, per the meter, even at loud levels...my speakers are rated @ 90 db efficiency....I imagine the idle temp and "max" temperature of the unit are pretty much identical, as that is the design of the bias and heatsinks.... |
Jim Bob the coda gear sounds better then the pass gear which tends to sound a little too warm The coda amps sound warm but are a touch more neutral then Pass Labs amps The coda is configurable so you can choose yrour total power and amount of class a power that you need Also thecoda amps run warm but don’t heat up the room At any time you can send the amp in to coda and they can re bias the amp The reviewer Terry London found the 6k coda .8 poweramp came shockingly close to a 14k pair of pass mono amps https://hometheaterreview.com/coda-technologies-continuum-no-8-stereo-amplifier/Dave and troy Audio intellect nj CODA DEALERS |
I too have the X250.8 powering a pair to Thiel CS2.3 which are about 87dB efficiency.
I agree with @jw944tst. It doesn't get HOT but does get warm to the touch. In summer my room (12ft X 19ft X 8ft) does get warm at night when listening for a few hrs. but not running the AC. I live in the NYC area with warm, humid summer nights.
Moving back to Colorado this month where the dry air cools down much more at night and I doubt I willt notice it very much. Probably depends on where you live. The amp is pure heaven though, well worth the extra warmth it produces in the summer
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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! |
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. |
@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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