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What is missing here?

In this months Absolute Sound magazine there is a nice review of an amp that many of us would probably consider based not only on the review but on the topology utilized with the amp. The amp in question is the new Air Tight ATM 300R. This amp utilizes the 300B tube and according to Dick Olsher " The Air tight ATM300-R wowed me with countless hours of listening pleasure. It consistently brought to life the full sonic promise of the 300B". Sounds amazing right??


Except, nowhere ( except in the specs section) does it mention that this amp is limited to 9Watts/Ch!! And at that it is putting out about 10% distortion! So not only is the amp severely limited to which speakers one can match it to, but those speakers had better be ULTRA high efficiency. While most experienced a’philes will expect the extremely severe limitations of this kind of max output, how many casual listeners who read this article will realize the extreme limitations that this amp comes with? Certainly none of that is mentioned in the review, which brings up the question...why not??? How many even somewhat seasoned a’philes have made the mistake of matching a flea powered amp with a less than favorable speaker load? Let’s hear about it....
128x128daveyf
freediver
1,195 posts
 
If you had told me the price up front I could have quoted the ending pretty much word for word without ever reading the review,though it is missing the comparison to an even more expensive amp that was much better overall...
larryi
3,992 posts
 
Nine watts per channel is about right for a single-ended 300b amp.  I would actually be more comfortable with one rated at a LOWER output, assuming that the lower rating means that the designer is intentionally not pushing the output tubes very hard.  Tubes last dramatically longer when they are driven gently.
atmasphere's avatar
atmasphere
11,807 posts
 
The thing is, if you want to get the most out of an SET, the speaker needs to be so efficient that the amp is never asked to make more than about 20-25% of full power. Otherwise higher ordered harmonics start to show up on transients, causing the amp to sound 'dynamic' since the ear uses those harmonics to sense sound pressure. So this comment is problematic:
For an 87dB speaker, 8 watts will give you 96dB at 1 meter. Pretty loud.
If you're buying a 300B amp, you'd have to have done some research.
Why attack low-powered amps rather than inefficient speakers? ;-)
because you really don't want to run the amp to full power. Put another way, to get that same sound pressure properly (keeping the amp power to 20-25%), you would need a speaker that is about 93-94dB.


Of course, a 7 watt SET (a 300b won't make 9 watts unless class A2) struggles to have full bandwidth due to how severely the output transformer limits bandwidth as the power is increased. This is why the 2A3 (2-3 watts) is considered a 'better' sounding tube and the type 45 (0.75 watts) even better than that. The less practical SETs become, the better they sound! Of course, the speakers needed for such amps need considerably more efficiency and so bass becomes a problem...
daveyf's avatar
daveyf OP
2,871 posts
 
@atmasphere  Thanks Ralph. Your post explains a lot and is certainly very instructive. Apparently the amp has 10% distortion at 9watts. I would have to believe that this is audible. Therefore, a match to the most efficient speakers one could find would seem to be mandatory. Probably only a match to a horn design would be indicated...leading to the other issues you mention.
None of this is discussed in the review, I have to question why?
atmasphere's avatar
atmasphere
11,807 posts
 
None of this is discussed in the review, I have to question why?
No idea- best to ask the reviewer. IMO/IME its a pretty important (might have wound up edited out) omission!
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