Zero Feedback: Atmasphere vs. BAT

Scottlanterman - I read very positive review of Atmasphere (MA-1) but what makes them hot is amount of current that tube heaters consume. Each tube is about 6.3V 2.5A and there is 28 of them total. That equals to 441W dissipated power just for the heaters. Total power dissipated might be in order of 1kW.

Zero feedback OTLs ???

Hello Marakanetz,

If you look at the Atmasphere website they espouse very low to zero feedback and they claim to have achieved it. These guys often get very high praise by audio clubs that are not part of any audio magazine. I emailed them, and they do respond really well and are helpful even when dealing with someone looking to buy used gear. I think BAT is also very good from reputation and review. I wonder how they compare sound wise since one is AB the other is A?

Scott

I know VK as an engineer. No doubt about him. They use differential driving stages(balanced circuits) and classic push-pull output design that really doesn't need deep negative feedback just like most of the tube amps.

I also know that to achieve transformer-less low tube output impedance, you need deep negative feedback.

I'm not looking to buy Atmasphere equipment since it's not only within my budget, but it also too much heat, too much tubes to roll(upkeep) and lots of idle power consumption.

A few obserrvations based on 8 years of ownership of Atmasphere amps (M60s) and preamp (MP-1)

I spent 45 minutes on the phone this morning with Ralph. A friend of mine just bought used MA-1s and wanted to know if they have negative feedback. The answer is none. More importantly, I have never run across a company of any type run by people who are more accessible and available directly on the phone or via internet than the guys in Minnesota. You just about have to hang up on 'em to get rid of 'em! They desperately want you to be satisfied with your purchase and are in it for the long haul.

Heat output. I agonized over this for quite a while but finally pulled the trigger in 2000 and bought my monoblocks. I live just outside of New Orleans and, with the possible exception of Death Valley, nowhere in the contiguous 48 is hotter AND muggier than here. Honestly, it's a non-issue. They do put out heat but it just doesn't seem to affect the comfort level in my listening room summer or winter and I don't note any change in my A/C run time when I'm jamming. My friend with the MA-1s has a much smaller room than I and, unsolicited, made the same observation less than a week ago.

The Atmasphere sound can be characterized as purity incarnate. Purity is the holy grail of audio in my book. Purity is the single word embodiment of a whole slew of other audiophile destinations such as transparency,tone, musicality, dimensionality, etc. It's THE one descriptor to possess, IMHO. It just makes sense that eliminating one massive electronic "processor", if you will, should facilitate a cleaner, more direct connection with the music.

Finally, this all being said, I have nothing but respect for BAT. I have never heard a disparaging word about the company, its people or it's products. I have one friend who just bought a VK 600 to use with his Salk speakers but I've only heard it once and under very suboptimal conditions.

The usual caveat, of course, with the OTL design is that it needs to be partnered with impedance friendly speakers downstream. I'm running AG Duos.