What could I expect to hear from a Class A amp?

I do appreciate the technical explanation. On one hand it's about education. On the other hand it builds credibility to one's belief. From what's expressed thus far, can I take it that Class AB has more issues to overcome? The combination of designer skill and his stand on debatable subjects makes it difficult to come up with a comparable sound delivery system. Whereas Class A design is more simple, but with the problem of heat and power consumption.

My second question if I may would be what enables Class A solid state design to incorporate the strengths of tube amplifier concept with less of the problems. Is it because of shared design? Somebody mentioned about 2 tubes and a resistor.

Ferrari, I must agree with you about the exemplified work done by Nelson Pass on Class A design. I own the XA60.5. Based on his paper, it appears that primary difference between the X.5 and XA.5 is less on circuitry, and more about higher current bias setting for the XA.5. Secondly, people have contrasted the 2 series just like Muralman1 did. Thirdly, nobody receives such level of praise when it comes to bridging the gap between SS and tube amplifiers the way Pass amplifiers do. Yet with good end results we suspect Class A design is responsible for giving SS that wonderful tube sound without the overkill. Thus for these observations I tend to think Class A design is the way to go on amplifiers, as it provides the superior foundation. However there are enough unknowns that it's up to the astute designer to finish the job. There is only so much mathematics, theories, and the oscilloscope can explain.

Well it sure sounds like I am advertising Pass amplifiers, am I? It would be nice to hear comments from people who own non-Pass Class A amplifiers, especially when the author of this thread was wondering about Krell. It would be nice to balance personal bias when hearing contrasting opinion.

Could somebody please comment about the 24/7 operation needed for Class A. Typically I heard that you want to warm it up for 30-60 minutes. Yet it seems to take about 4-5 hours before my ears could not distinguish a difference.

I definitely agree about the non-fatigue factor since your brain does not have to fill in. Before getting the XA60.5, it's like a love-hate thing I have with the stereo. I must listen to it because I love music. But about half an hour later, I got tired, somewhat disappointed, and turn on the TV instead.

I should have made it clearer. The 4-5 hours is going from standby to full power on. The standby mode is just not enough. So to rephrase the question, did you find the standby mode insufficient to let 30-60 minutes at full power to finish the job?

On separate issue, would all that heat for 24/7 at full power take toll on the circuit board? Of course the counter arguments would be the on/off as you said, and the expansion/contraction fatigue cycle due to the hot/cold. Do you know what's the typical age of a class A amplifier before the heat kills it. At least the XA60.5s are hot but not that hot.

I'm confused about the comment on Henry Ho. The DAC is either positioned between the transport and the preamp, or is part of the preamp itself. Yet we are talking about the amplifier here. It comes across that you actual benefit from improvement to your source instead.

It seems I have to continue putting up with listen to music late at night after giving the system most of the evening to warm up. I didn't have the time yet to read carefully the thread on whether to power on/off (thanks, Almarg) just yet. But from what gathered, it seems like a hot debate. Also water evaporation on the electrolytic capacitor is a time-dependent thing. The longer it stays hot, the more time for water to evaporate. Yet regardless of where the truth lies, leaving expensive equipment on and unattended at the risk of power outage and surge is asking for trouble. Does anybody have positive experience using a constant power source to drive your equipment. I once tried a hefty computer battery. It sure kept the equipment on regardless, but the sound is awful.

Kirjanki, during that 4-5 hour warm up, sound quality fluctuation is serious. It can sound pretty good almost at start up, then sound hemped in again a few minutes later. Of course it still sounds better than the previous amp. despite the fact; however, that's not the point here. As to placebo effect, my hearing capability definitely changes from moment to moment. But this 4-5 hour waiting period has been going on for some time now. This definitely isn't so before I got the XA60.5, and behaves as such immediately right after I start using the XA60.5.

Kijanki, this waiting does happen during the day, on the weekend as well. You are correct about me being picky. Yet it seems that if I want to get the typical benefit of class A, I'll have to wait. Otherwise it sounds closer to my former class AB amplifier which is not bad really.

It would be nice to know of non-Pass Class A amplifiers that perform well, and why so. Bearotti asks about Krell. At this point I am curious in just about anything Class A. The whole discussion thus far is very helpful to me as a Pass XA60.5 owner, but thus far continues to confirm what's heard through the months, in that nobody remotely comes close to Pass Lab on Class A amplifiers. Otherwise there would have been well-informed and fairly objective challenges left and right.

I did listen to Clayton's at a show. It blends in among the good amplifiers. It's interesting to note that big players have not caught on to Class A in big ways. May be they figure the R&D it takes to compete against Pass take so many years that it's not worth the risk. The little guys are still at Square One and thus don't have much to loose. Just pondering here.