Zero Feedback: Atmasphere vs. BAT

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.

It's a tough choice. I think if I want Atmasphere amps I will sell my Spendor's which I really like for their natural sound. I would look for something that could run on the M30, I thought that AudioKinesis Jazz Modules looked good with an M30.

I think with my S8e's I could enjoy BAT VK75 and then try a second and run Mono down the road if more power is required.

The question is should I sell and go with horns and low power class A? Should I keep what I have and go with something like the VK75? "Gold Plated Decibels", maybe that is what keeps the common man from having a world class system. Bottom line you may need effecient speakers to have the best gear feeding them at a reasonable cost.

That's where I am at today. Been listening to Spinnerette, Ghetto Love to distract me as I think about system re-design.

Thanks for your input.
Scott

Scott- Both of those amps are balanced. Are we correct in assumming you have a true balanced output pre-amp? I had a BAT pre-amp a few years ago and then a pair of M-60s. (BTW, its an s-30 stereo amp @ 30 wpc or an M-60 monoblock pair at 60 wpc). Both are quality products w excellent support; I would say that Atma is next step up from excellent, whatever that is. If you send a used product back to them for a check-up they will re-warranty it. Ralph was also very helpful when I was considering sending a used R to R tape deck to him for refurbishing. He actually advised me that the cost of having him do the work would greatly exceed the potential return. The Atma amps are pure class A and IMO do heat up a room, but so will a pair of the VK-75s w those huge output tubes. I've had a Joule VZN-80 that has the same complement of output tubes as the BATs, I'm pretty sure. They both get HOT!!! FWIW, Duke @ Audiokinesis also offers outstanding support. He sells Atma amps among others. Based on his contributions to this site, I would expect him to give you a very honest assessment of the differences between those two amps driving his speakers.

The BAT topology is not exactly push-pull, but rather single-ended floating bridge(similar to Atma-Sphere), as described by Victor Khomenko:

"The VK60 is neither a traditional single-ended design nor a push-pull design. We refer to the VK-60 through VK-1000 amplifiers as single-ended bridge designs. This fundamental circuit dates back to the early 1950's and was invented by Henry Wiggins while working for the ElectroVoice Company. The original name for this type of output topology was Circlotron. The single-ended bridge design relies upon two single-ended amplifiers arranged in a floating bridge formation. This differentiates it from other forms of bridge topologies, most of which effectively incorporate two push-pull sides. The output circuit is inherently balanced and is driven differentially from a preceding stage. The two DC bias currents that exist in each half of the output stage cancel each other in the load. It is a more expensive way of building an amplifier as it requires multiple floating power supplies, as opposed to the more traditional ground-referenced supplies. The benefits of this approach, however, include enhanced symmetry when compared to push-pull designs and lack of the DC saturation problem inherent to single-ended designs."

After hearing an Atma MA-1 I was ready to sell my VK-75SE, but instead set about modding the piece to the point that I feel I'm getting similar performance. Both manufacturers provide excellent customer service, with Ralph at Atma going the extra mile regarding customization, upgrades, and long-term personal relationships with customers.

You can't go wrong with either of these similar designs. However Atma OTLs need to be closely matched to speakers with benign impedances, and they do run hotter.