Anyone compared BAT Rex vs. Atmasphere MP-1?

Obviously, there is a big price difference between the two(not as big used). But, these two are likely to be in the top of the true balanced, fully differential, reference preamps available.

I'm mostly interested in the sonic differences anyone would have noticed switching between the two in their own system.
I doubt you're going to find someone who has compared both in a variety of systems over a lengthy period of time - even top-notch preamps generally have a subtle effect on a system and take months to properly evaluate. I would draw out any person who directly responds to your question about the other components in their system, their listening room, whether they have treated their A/C power supply, the type of music they listen to, etc.

At this level, both of these preamps are going to be superb, and synergy and features should be your focus. If you have long IC runs (2+ meters) to your amp, I would be inclined to consider the top solid-state pre's in order to avoid the impedance issues and problems running long cables that almost all tube preamps (except those using output transformers) suffer from. I would insist upon a preamp that has a polarity switch, and perhaps one that allows you to set input levels independently for each input so as to avoid gross differences in base volume levels among various source components. I don't much like preamps with tube rectification (I think the Rex; not sure about the Atma-Sphere) because I can't keep them turned on 24/7.

I would add to your list of reference-level, truly balanced preamps the Rowland Criterion, ARC's recent-production reference preamps, and Pass's top preamp. The darTZeel preamp is not balanced (Herve Deletraz hates balanced circuits), but it does feature an XLR output on an output transformer, which confers the noise-suppresion benefits of balanced operation for running long IC's. I run a Rowland Coherence II (which is fully differential balanced and battery-powered).
I have a BAT REX and love it. It's in an all BAT system (synergy). Other than its sound which is superb, I love the remote control and the ability to tweak with NOS tubes vs. current manufacture. Different strokes.......
Raquel is right. Maybe there is someone out there who has compared these two pre-amps. I am not one of them.
08-27-10: Raquel
If you have long IC runs (2+ meters) to your amp, I would be inclined to consider the top solid-state pre's in order to avoid the impedance issues and problems running long cables that almost all tube preamps (except those using output transformers) suffer from.
Both these preamps are fully balanced/differential from input to output. No output transformers(Ralph Karsten doesn't use them in any of his products). The MP-1(& MP-3) put out 32v@600ohms, the Rex 200ohms. The Atma preamps are claimed to easily drive cables of up to 200ft long. So, cable influence is essentially a non-factor when run to true balanced inputs of a power amp.
Output impedance measurements for tube preamps are typically made at 1 khz., and the story will usually be very different at the frequency extremes, especially in the low bass. As for the BAT Rex, Atkinson's measurements in Stereophile revealed, "[I]ts output impedance was a little higher than specified, at 1000 ohms at 20kHz, 415 ohms at 1kHz, and 4.8k ohms at 20Hz. The last is due to the necessarily finite size of the output coupling capacitors. As MF noted, it should not be a significant issue in listening to music as long as the power amplifier has an input impedance greater than about 50k ohms." Atkinson's measurements of the BAT VK-51SE revealed similar performance.

Generally speaking, you need ten times the maximum output impedance of the preamp as compared to the input impedance of the amp to avoid frequency roll-off, i.e., this is why Fremer and Atkinson state that a BAT Rex with a maximum output impedance of 4.8K ohms needs to be used with an amp featuring an input impedance of 50K ohms or higher. There are a lot of amps featuring input impedances of less than 50K ohms, so this is going to be an issue at times.

I know that Atma-Sphere pre's don't use output transformers. Perhaps Ralph can explain how the MP-1 get around this problem?
Aaah, I get what you are saying now, thanks for the tip. Luckily, everything that I am considering is 100k and up.
Sonic attributes of the Rex include:

Very dynamic, clean, energetic.
Highlights midrange texture and harmonies.
Bass is excellent.
Treble is open and extended.
Noise is very low.
Very powerful sound.
Switch between 6C45 and 6H30 provides two flavors.
Build quality is at the top.

Those looking for warmth and forgiveness should look elsewhere. This will dig deeper into the music. I have no clue why people say BAT is 'dark'. I would never charactarize this preamp as dark.

Adding NOS 6H30DRs will up the excitement factor (2 out of 8 in the power module is enough for me).

I think the Joule LA450 and the Audio Reference Anniversary Preamp could be intriguing alternatives, but I have not made a comparison and am not particularly concerned to do so at this time.

I am not familiar with MP-1 except its excellent reputation. I am familiar with REX and its the best (along with my current Joule-Electra LA-300ME) preamp I ever auditioned or used.

When I heard REX first time (using my reference tracks) my jaws literally dropped to the floor. Word "magnificent" is understatement.

Regarding the long cables - its the best if you call Victor. In this situation,I would not care at all if preamp balanced or not but if it has a buffer driver. Victor is perfect man to address your specific concerns, He is extraordinary nice person (well may be not in all his writing... ;--) ;--) He will help you and advise you. You meet daily at "Outside" and Victor will do everything he can to help you in any way possible.

Good Luck !
Rtml, thank you for the great description. I find myself leaning towards a more rich(not overly-ripe, though) and powerful sound. I had considered ARC, but since I will be buying used, I didn't want to deal with trying to decide between the Ref 2, 3, 4, or 5 to find where the "sweet spot" for price versus performance was.

Simontju, I will ask Victor. He is always great with technical advice - whether about his products or just engineering in general.
Hello Darkmoebius,

Just wanted to take the opportunity and give a plug for the BAT Rex. I don't think you'll find a preamp that dives deeper into the texture of sound as the BAT Rex. That's what I consider detail!

At the same time it does it with such a sense of authority and grace, never blinking an eye, a feeling of ease to the sound that invites one to listen in to the music. For me it is such a pleasure to own and I wish you luck finding a pre that you'll feel the same about.

I would like to ask Raquel to elaborate on the Rex not being able to be on 24/7. The reason I ask is that I have mine on 24/7 (breaking in new speakers) and you have me worried. :-)

Some tubes in some tube power supplies can pass a relatively large amount of current and will wear out like output tubes in a power amp will wear out (certain tube preamps actually use output tubes in their power supplies - the ARC Reference 3 uses a 6550, and I believe the big multi-chassis Jadis used to use EL-34's). For example, when Stereophile reviewed the BAT Rex, they went through a couple of 5AR4's in the power supply over the course of several months of leaving the preamp on 24/7 (which they evidently did at BAT's suggestion). The review suggests that the BAT is fused to protect against tube blows in the power supply - you need to consult your owner's manual or ask BAT whether 24/7 operation poses a safety issue.

The other circumstance in which I would tend to think twice about 24/7 operation in a piece of equipment using small-signal tubes (i.e., tube preamps, tube DAC's, tube tuners) is if the tubes are run near their maximum voltage rating. Basically, such a tube will face the same wear issues that an output tube in a power amp will. It did not escape me that the Rex is said to run really hot, but this could be nothing more than the fact that it has a ton of tubes in it - I don't know how its various tubes are run relative to their maximum voltage ratings.

If, however, a tube preamp has solid-state rectification and does not feature a hot-rodded tube circuit (that would be the vast majority of them), I will run it 24/7 in order to maximize sound quality and tube life. As for why 24/7 operation would extend tube life, please see my comments about small-signal tubes and tube performance in the following thread:

I hope this helps.
Raquel, just for clarification, the BAT should be left on standby when not in use? Just not 'on' 100% of the time. One could turn it off if going away for some time.

I thought the initial surge of current into a cold tube was the detrimental factor.

I also hear no sonic difference within 5 minutes of coming from totally off, vs. 5 minues of coming out of standby.

I'm not sure why Stereophile had problems with the 5AR4s. These Sovtek tubes cost $20 each, so it is not a big deal. Nonetheless, something must have been not quite right, and I agree to burn-in the unit for a few hundred hours for a review. Also, it is practically unheard of for a NOS GZ34 to die. Some of these have been in operation for a few decades.

You wrote "Raquel, just for clarification, the BAT should be left on standby when not in use?" I cannot answer this question - you would have to ask BAT.

Again, it is generally much better to leave tube equipment featuring small signal tubes turned on 24/7 in order to maximize tube life, but as explained above, if the piece features tubes in the power supply like the BAT Rex, or operates the tubes in the circuit near their maximum voltage, you may be better off turning the unit on and off.

When you write "[N]onetheless, something must have been not quite right, and I agree to burn-in the unit for a few hundred hours for a review.", I'm afraid I do not understand the idea that you are trying to convey.

My apologies to the author of this thread for the tangent about tube maintenance. As to how this issue applies to the two preamps you have inquired about, the Rex has been discussed. As for the Atma-Sphere, I'm pretty sure it uses solid-state rectification, which, in combination with its use of 12AT7's and especially 6SN7's (they were used in televisions and are extremely robust), would make me run it 24/7. If it were me, I would probably run a Rex 24/7 notwithstanding everything written above unless BAT strongly disagreed, but based upon the Stereophile review, it looks like BAT has no problem with 24/7 operation of this preamp.
No problem with minor tangent of discussion, Raquel, as long as it is informative. And your points fit that definition to a "T". You have given me a lot more to look into before making an expensive leap.

I still need to nail down which speaker genre I want to explore(having tried SET & high(er) efficiency wide-range driver) - electrostat/ribbon, line array, multi-way cone driver. I'd like to try a fully balanced/differential system from source to speaker. But, that may be hard when it comes to phono preamps(except maybe Atma-sphere)

I can think of a few other fully differential balanced phono stages: BAT, Einstein, Rowland. I run a Rowland Cadence.
Raquel, the way the MP-1 works is it has a direct-coupled output. The output impedance is low enough that it can drive 32-ohm headphones easily. It is designed to drive 600 ohms without effort; obviously its output impedance has to be well below that in order to do so.

Because its outputs are direct-coupled, the output impedance is flat from 1Hz to 200KHz or thereabouts. So it really can drive 200 foot interconnects without difficulty.

It my opinion that getting rid of the output coupling caps is the single best thing you can do with a tube preamp to improve transparency and bandwidth.

The MP-1 was/is the first balanced line preamp for high end audio. Victor's business partner bought one of the first production units before they went into business together. He had some of our MA-1 amplifiers too- we still have his warranty forms on file.
Thank you, Mr. Karsten. Incidentally, does your MP-1 use solid-state rectification, and I wonder what the voltages are, relative to maximum recommended voltages, on the 12AT7's and 6SN7's (BTW, are the 6SN7's standard or GTA/GTB's?)? If this information is proprietary or you do not wish to respond for whatever reason, my apologies, I do not mean to pry. My question goes to the issue of tube life and running the unit 24/7 - I would think, assuming moderate voltages and solid-state rectification, that 24/7 operation on this preamp would maximize tube life. My rationale for this is set out in my comments to the following thread:

Best regards.
The preamp is designed for 24/7 operation. IMO you get better bang for the buck when the preamp is operated when you are playing music, rather than using up the tubes while you are at work or asleep in bed.

It warms up quickly, much faster than in years past, due to better regulation and better coupling caps. Two hours is more than enough for the preamp to settle out so 24/7 operation really doens't win you anything with it like it did 10-15 years ago.

The power supplies (8 of them) are all tightly regulated so the use of SS or tube rectification isn't relevent; the rectification is all handled by HEXFREDs. The highest voltage drop on any tube in the unit is about 150 Volts, the B+ and B- are both regulated at +/- 250V.

The 6SN7s in the unit tend to last about 10,000 to 30,000 hours (GT, GTA or GTB, although seriously we don't know how long the 6SN7s last; some seem to last literally for years). The 12AT7s (used only in the phono) tend not to last as long. IF you run the preamp 24/7 we used to recommend replacement of the 12AT7s every 4-5 months; in the Mk 3.1 (the latest version IOW) they seem to last considerably longer but the preamp is so recent (came out a year ago) that we don't have good numbers on that.
Mr. Karsten: Many thanks for your responses. The 6SN7 Sylvania chrome tops in my VAC Renaissance amp, used as driver and splitters, are beginning their eleventh year of use (in on/off service), and for all I know, they may have previously seen service in somebody's T.V. :)
Just a couple of quick notes here, don't mean to overburden the forum.

One - regarding the extended tube life with 24/7 operation... while a common opinion, it is most definitely not universally agreed upon or shared. One could construct many different cases, but in my opinion, in ***general*** in normal home environment turning the equipment ON and OFF will produce longer tube life.

Furthermore, continuous operation will, without any doubts, shorten the life of most electronic components. Whether this is justifiable by potentially shorter readiness times - is up to the individual user to decide.

Regarding the 5AR4 tubes - their quality level is generally quite high, but we certainly went through a less than spectacular batch. As the manufacturer, we do our best trying to shield the customer from such problems, but that is not always possible in timely fashion. For instance, we stopped using the Sovtek 6V6 tubes entirely, at one point. But some problems only manifest themselves weeks or months down the road.

All tubes in BAT equipment operate with very significant deratings. The output 6C33 tubes operate the hardest, at about 60% of maximum stress, other tubes are typically used at far less than 50%.

Victor Khomenko
Raquel, yes, those old 'chrome dome' tubes are pretty impressive- I've seen them as original parts in equipment that is over 50 years old, still testing as strong as new tubes. We have seen them go over 50,000 hours in our stuff and I would not be surprised to find out that some of them could do over 100,000 hours in the right circuit. They sound nice too :)
Mr. Khomenko:

Thanks for the input on the issue of tube life and 24/7 operation. My experience is that, while most people are aware of a debate regarding 24/7 operation and solid-state gear, few people who own or sell tube gear are aware that some manufacturers advocate 24/7 operation of equipment using small-signal tubes in order to extend tube life (my posts on this issue tend to create surprise).

Assuming the conditions necessary for 24/7 use are present that I describe in the links referenced in my posts, the only thing I worry about operating 24/7 with either solid-state equipment or small-signal tube gear (aside from not being home to disconnect equipment when an electrical storm passes through) is what it's doing to the caps, which tend to be rated for only a few thousand hours, but caps will often far outlast their ratings and are relatively cheap and easy to replace, while thermal cycle damage to transistors from on/off operation, particularly where the transistors have gone out of production and the amp thereby becomes worthless, or thermal-cycle damage to irreplaceable, cherished NOS small-signal tubes, is not cheap. If I owned BAT gear (and I may one day, as my system is fully differential balanced from turntable to amps - that's why this thread, about BAT and Atma-Sphere gear, caught my eye), I would follow your instructions and turn my equipment on and off. With all due respect, however, your advice does run contrary to the evidence I have described in my posts referenced above and in numerous other posts I have made over the years here.
As usual, this thread deviated from the original question- comparison of BAT REX and Atma Sphere MP-1 (MK III?).
I'm another one who would be interested in this topic.
As many others here, I've had BAT REX in my system for a significant period of time, and so far, it's the best preamp I've ever heard (others include Supratek, Nagra, Doshi).
MP-1 I only heard under show conditions, so I have no opinion really. It's intriguing to me, since it's a full-function preamp.
So, maybe somebody could offer an opinion on it? At least not in direct compar. with REX?
Hi Raquel,

This is the question that does not have a simple answer. As one of my teachers used to say - when in doubt whether simple rules apply, consider the extreme cases. Would you keep your units on 24/7 if you only listened to them for two hours once a month? Probably not. We, therefore, can safely assume that for the multitude of applications and uses there also exist multitude of correct answers.

There are several kill mechanisms acting upon the tubes (and other components), and you correctly mentioned one of them - thermal cycling. However, there are others. Of them the cathode wear might be the most important. Needless to say, both the full operation, and the typical Standby, have the cathodes working, and therefore wearing out.

Furthermore, as is known from the reliability studies, temperature always accelerates the component failures. Its effect is exponential, and its degree varies depending upon the component's nature, but it is always there.

Also, while it is true that thermal shocks are, generally speaking, damaging, it is the rate of change that is the most critical aspect of that particular effect. There are special accelerated life tests that include high rates of temperature change, and they have been shown to be effective predictors of product reliability. However, the rate is the key element here.

By controlling the rate we can reduce the damaging effect of thermal cycling manifold - also exponentially. Therefore it is always important to understand how the product handles the changes of its state. In our particular case the tubes heat up very gradually, so the rate of temperature change is substantially reduced.

All this would of course be academic without hard experience, and that experience tells us that we do not see tubes die catastrophically after 10 or 15 years, as the rule. And damage due to thermal cycling tend to manifest itself as catastrophic failure.

What we normally see is slow deterioration of tubes, most likely due to the depletion of their cathodes. Meaning - long operating hours.

As there is no simple answer, every user has to develop his own way of operating the components - we just give him the tools. All I am trying to express here is the fact that no single universal truth exists in that regard.


09-01-10: Maril555
I've had BAT REX in my system for a significant period of time, and so far, it's the best preamp I've ever heard (others include Supratek, Nagra, Doshi).
I have considered those three preamps, too. Could you please describe how the Rex's musical presentation differed from them and others you've had the good fortune to use?
As usual, this thread deviated from the original question- comparison of BAT REX and Atma Sphere MP-1 (MK III?).
In this particular case, I find the discussions of tube life and 24/7 operation, while tangential to the original post, extremely relevant since both preamplifiers use 18 tubes each. I have read about amps/preamps who require retubing every couple of years at fairly high expense and would like to avoid that.
Again with apologies to those who are bothered by this tangent, I think we are actually saying much the same thing, Mr. Khomenko. I have or had mentioned in this thread and/or others that:

(i) operating voltage helps determine tube life, i.e., the more voltage a tube sees, the hotter it runs, and the quicker it will normally die; and

(ii) in order to avoid the sudden, deleterious application of voltage to tubes upon start up, some tube equipment - including your products, I am now learning - features a "soft-start" function that brings up power gradually.

Since we're on the topic and your Rex preamp features tube rectification, I should mention that tube rectification functions like a variac to bring up power gradually.

Not to belabor the point, but based upon the evidence I have seen, GENERALLY speaking, if the small-signal tubes in a given circuit are run at reasonable voltages (i.e., well below their maximum rating and they thus run cool) and the piece uses solid-state rectification without a soft-start or standby feature, which is the case, in my experience, with most tube preamps, 24/7 operation yields better tube life (and better sound). I again quote from the owner's manual of my VAC Renaissance tube amp:

"How long should tubes last? It has long been known in professional circles (and probably now forgotten) that a tube such as the 12AX7 will display BETTER performance characteristics after TWO YEARS of CONTINUAL operation than when it was new. In normal use it is not unusual for a low level [small-signal] tube to last 5 years or longer. Output tubes [i.e., power tubes used in tube power amps] are another story, as they are continuously providing significant amounts of current." (Emphasis original).

Incidentally, if, because of work demands, I know that I'm not going to be listening to my system during a period of a month or more (a common scenario for me at year-end), I will indeed t
Raquel, I think with older tubes the quote might be accurate. But with modern signal tubes, particularly low level miniatures, there is a phenomena of grid contamination that has to do with the inclusion of contaminates during the assembly process. An excellent example is fingerprints when workers are not given latex gloves or the like for assembly.

In such cases (if you are using tubes with this or similar issues) leaving the preamp/amp on 24/7 is not really all that helpful, as when the grid contaminates the transconductance will fall off sharply.

Its really not a good idea to design for tubes that are out of production, unless as a manufacturer you have no concerns about the owner being able to find tubes for the unit 20 years down the road. IOW its a good idea to design for tubes that are currently being made, so using such tubes has become a fact of life.

We have seen this contamination problem with 6SN7s, 12AT7s, 12AX7s, 6DJ8/6922 and a few others. It is considerably more rare with NOS types.

I'm just pointing this out because 24/7 as a generalization is not always the panacea for best performance.

As an additional FWIW, the issue of cathode stripping is far more pronounced with power tubes. It is a matter of controversy as to whether its a problem for small signal tubes.
"will indeed t ... urn everything off." Sorry about that.

Messrs. Karsten and Komenkho: Great stuff - thank you. I look forward to the debate about cathode wear and small-signal tubes the next time you sit on a panel together!
This is a very abbreviated version of my experience with the above preamps:
Supratek: dynamic, fairly resolving and involving, but is not completely neutral- it did have very annoying (to me) mid range glare on certain recordings. After many debates I suspect, that it suffered from some kind of chassis generated resonance (it does have fairly thin metal bottom plate), and some members reported improvement of the glare with the use of the wooden part of the chassis for support.
Nagra: very refined, involving and musical. It does have slightly different (forward) soundstage perspective, but is not bright.
Doshi: neutral and well balanced, but left me with an impression of lacking dynamic impact, compared to Supratek and Nagra, and especially to REX.
REX: It does NOT have any flaws IMHO- extremely dynamic, beautiful tone, very balanced (no pun intended), mid range is absolutely to die for, resolution in spades, bass, you name it- it does it all. Overall, it's a different class of music reproduction, compared to others.
I lied, it does have a few flaws- it is line stage only, hence an additional expense of the separate phono,
it runs pretty warm,
and it costs $22k now.
I still feel, one day I might have it in my system again, it was that addictive.
09-01-10: Maril555
REX...I still feel, one day I might have it in my system again, it was that addictive.
Oh my, that just feeds into my obsession.
Just to add my 2cents for this duscussion..

I'm a happy owner of BAT 52SE (a "little brother" of REX). I would also describe this "house sound" as breathing transients, superb textures and very resolving. Nothing compared with usual "tube coloration" as probably one likes. Just pure music window... It's so amazing clean in my system even with relatively cheap Proak D15 speakers.

Never read an average review for REX - it is outstanding always.
Maybe Victor's business partner can provide a view on the MP-1. This thread seems to be heavily biased towards the BAT...
"Maybe Victor's business partner can provide a view on the MP-1. This thread seems to be heavily biased towards the BAT..."

Hello Rob,

Besides BAT making some of (IMO) best sounding components your money can buy they also set the example of class and professionalism. I've never once seen Victor or the other principals of BAT use a public forum for self promotion.

If Victor responds to a thread about BAT equipment it is always factual and technical, and its intent is meant to be truly helpful. No subjective opinion on he feels his components sound, especially compared to his competitors.

My apologies if this too far off from the original subject matter.

I love that BAT owners love their BAT gear, and the discussion
of the technical issues and contributions by both Victor and
Ralph have been marvelous to read, but I still see no comment
by anyone who has listened to both the BAT Rex and the Atma-
Sphere MP-1. For my part, I've only listened to the Atma-
Sphere MP-1 and the BAT VK-51SE, and not in the same systems.

Can anyone address the original question?
I know MP-1 well in my own system into modded BAT VK75SE and Merlins, and at CES heard BAT Rex preamp into BAT Rex monoblocks and Wilson Shashas. A minor case of penis envy.
Could you share your impressions of MP-1 in your system?
Maril555, my MP-1 is a modded MkII that replaced a BAT VK5i and VKP10. The main thing about Atma is the sense of wide open bandwidth and agility, as compared to the mellower & prettier sound of BAT. However at CES BAT REX components were fast on their feet, effortless, yet a bit fuller in embodiment than I hear at home. Of several exhibits this was the only one that had convincing synergy with Shashas. In other contexts at THE Show I heard MP-1 Mk III sound remarkable with Classic Audio Reproduction field coils and VPMS. It's a close horse race.
I heard MP-1 in the same room at THE Show with CAR speakers, and liked the room very much.
i agree with dgarretson that mp-1 are moreso than most any at being wide open, add they are great at chameleon. I've had loads of fun rolling tubes and finding what I like for certain disks to help "flesh out" or even "thin out" the musical presentation, at my discretion. great unit.
Ralph- I just saw (for the first time) your MP-1, but with a stunning brushed alum. finish. IF you had that available 2 years ago, I would be a proud owner. Well, hopefully my next preamp. Impedance wise, is the MP-1 a good match for Burmester 911 MK3?
Talk2me, There is no power amp made that has an input impedance too low for the MP-1 (it can drive 32-ohm headphones directly from the same outputs that drive the power amps). The Burmester is completely balanced, so no worries.