Atmasphere amps trustable?

Stevecham 8-4-2016 10:34 pm edt
... the ~4 Ohm output impedance still seems to a limiting factor; it's difficult to apply the ten-to-one minimal nominal speaker to amplifier impedance ratio often cited in order to maintain flat frequency response.

Many and I believe the majority of tube amps of all kinds will not meet that criterion.  For an 8 ohm speaker it would imply a damping factor of 10 or more.  Most high quality tube amps seem to have damping factors somewhere between 8 and 2 (with some being even lower than that), corresponding to effective output impedances of between 1 and 4 ohms or so, respectively.  (Audio Research and McIntosh tube amps are among the minority having DFs greater than 10, just a bit more in the case of most ARC designs and as high as the low to mid 20s in some McIntosh designs).

As you recognize, the 10:1 ratio you referred to will assure minimal variation of the amp's output voltage as a function of variations in speaker impedance over the frequency range.  However meeting that criterion is neither necessary nor desirable in many cases.  Assuming that the particular speaker does not require a higher damping factor for woofer control, meeting that criterion will be unnecessary and/or undesirable in the following cases:

1)The impedance of the speaker varies relatively little over the frequency range.  In that situation the amp's output voltage will vary relatively little as a function of frequency even if the ratio is much lower.   

2)The impedance of the speaker is relatively high at all frequencies.

3)The design of the speaker is such that the variations of the POWER it receives as a function of speaker impedance variations over the frequency range should be minimized for best sonics, rather than variations of the VOLTAGE it receives.  See Ralph's paper on "Paradigms in Amplifier Design."  While such speakers are in the minority, there are many such choices that are highly regarded.

4)Cases where the load impedance seen by the amp can be raised to a suitable level via a Zero autoformer.

Regards,
-- Al
 

Tubes are retro of course from the beginning.
They're noisy, require LOTS of wall power; generate LOTS of heat(especially OTL ones!) and LOTS of distortion(even considering even order ones) making the playback far from real. 

Tube components indeed sound different, but they're just toys and nothing serious no matter of reputation or credibility of one or another manufacturer.

Wow! You forgot to mention how tubes sound more natural than transistors though.

Just another DJ who judges sound by the spec sheet because they can no longer hear.
Zucka-Zucka , keep your pimp hand strong player!  ;^)

Nah, I'm just another casual dude who wants to listen to music and not play with toys.

Both times I have heard Atmasphere amps at shows, they were used with very large, very expensive high efficiency speakers from Classic Audio Reproductions.

First time in a small hotel room where the whole system was just a lot of overkill, more recently in a larger hotel ballroom where the gear had a chance to truly show what it can do and did it well.

I would like to hear the Atmasphere amps used with smaller high quality speakers that would tend to fit and work better in most peoples homes.

I have no doubt the results would also be quite top notch but the thing I wonder is if the results would be as "special" compared to others. I think of the Atmasphere products as very unique and special, not "weird", though they may look it to some.

IMHO, you have to really be a tube lover for whatever reason to live with any larger tube power amp with many tubes. TCO will be high due to power consumption and maintenance of tubes to keep things in peak operating order compared to other options ie SS.

High quality modern Class D amps of recent years are game changers IMHO. Not that they sound like many tube amps, but they do share some sonic qualities, are much smaller, have low maintenance and likely lower overall TCO (total cost of ownership) due to high efficiency, low power consumption, and no tube maintenance.

I use a tube pre-amp with 6 tubes with a Class D amp. I find this to deliver the kind of sound many tube amp lovers might enjoy with minimal use of tubes. Tube pre-amps are much more easily managed than high power tube power amps. I’d like to have no tubes eventually and am working towards that. My second system uses a true digital Class D integrated amp. The sound is quite excellent I think but will not be every tube amp lovers cup of tea for sure. I find this amp makes good quality dynamic box speakers sound like electrostats along the line of ML or Quad, but with better dynamics. I am using it currently with a pair of Dynaudio Contour monitors. Its a very interesting phenomena to hear how radically different the Dynaudios can sound in two different systems.

Also on my bucket list is to put together a third system built around a small tube integrated amp and high efficiency speakers. I enjoy putting together good sound in different ways, and on a small scale, tube gear is much easier to live with.

Absolutely untrustworthy!  I came home and found my girlfriend alone with them having a glass of wine with the lights down low!!!

But I will say, match them with the proper speakers and they make wonderful music. ;^)