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

Showing 2 responses by atmasphere

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!
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...