Atma-sphere MP-3 Preamplifier with Jensen 347 MC Transformers

Atma-sphere MP-3 Preamplifier with Jensen 347 MC Transformers

NOTE TO READERS: (Year 2006) Atma-sphere has been asked repeatedly over several years to comply with 10 Audio's policy on quotes (please see the bottom of the Home Page). They continue to refuse this simple courtesy.

This review took almost three years from concept to completion. I continue to be impressed with Atma-sphere's M60 mk. II.2 amplifiers, and was naturally interested in their MP-3 preamplifier when it was introduced about three years ago. Atma-sphere has a practice of continuous improvement and I wanted a mature version of the preamp, so I spent a couple of years with the CAT Ultimate preamp before looking seriously at the MP-3. There are five options available at the time of purchase or later. I was told the biggest bang-for-the-buck is the Teflon capacitor upgrade, and my second version (see below) included it. Other upgrades or options include Caddock resistors, a vibration dampening package for the metal cabinet, Jensen JT-347-AXT moving coil step-up transformers, and high voltage regulators.

Three major upgrades have been introduced since the MP3 under review was made in November, 2002. There are six tubes in the phono section, and the Cascode Mod, which is basically free, removes a pair of tubes and replaces them with plug-in jumpers. This reduces phono stage gain and noise, and noticeably improves the quality of sound from LPs. The second recent upgrade is the availability of Jensen 347 moving coil step-up transformers, of which my MP-3 received the very first installation. I asked to be a test case for the newly introduced Jensen model, and received one of the very first pairs shipped by Jensen, actually waiting an extra day or two for the new transformers to be potted before they could be shipped. The transformers add $750 to the MP3’s basic price of $3800. The third new upgrade is high voltage regulators. A fully loaded MP-3 with all these major upgrades lists for about $6900. I was quite disappointed that the intervening three years has not resulted in a more refined design, one not requiring so many upgrades to reach its potential. It is like an amusement park where the price of admission is surprisingly low, and then guests are charged extra for all the good rides.

My first sample of the MP-3 had a quality control issue with the white lettering on the front and rear panels: it flaked off with a slight rub of a finger nail. The very accessible and accommodating Ralph Karsten assured me that this was a one-off, unique error in manufacturing. When the MP3 was back at the factory to repair the lettering issue, I asked them to install the Teflon capacitor upgrade. I had listened to the stock preamp without the Teflon caps for a couple of weeks before the upgrade. The preamp was returned back to me quickly and the lettering defect never reappeared.

One day, a couple of months later, I was planning to do some serious listening, and turned on the system to let everything warm up for an hour or so. You know the ritual. As I was walking out of the listening room to my adjacent office, I smelled a familiar odor. Burning electronics. A resistor in the output power supply was heading south and smoking visibly. So back to St. Paul went the MP-3 yet again. All the tubes tested fine there, and the resistor was replaced under the warranty. NPF: No Problem Found. There is only one thing worse than having problems with a piece of electronic gear, and that is having intermittent problems that may reappear at any moment to ruin a planned listening session.

At this time, the new Jensen 347 transformers were just starting to ship from Jensen, and Ralph very kindly agreed to my request to install the pair I had ordered from Jensen. His installation of the transformers was beautifully executed. Again the turn-around was quick and I anxiously reinstalled the preamp into my system. Power on, and again, smoke. Luckily, I saw the smoke immediately and turned off the power. It turns out that one of the factory-supplied, stock 6SN7 output tubes had an intermittent problem. It worked fine at the factory, but not in my listening room. The resistor was still working, although it looked charred. The factory sent a replacement resistor (after the second request) which I installed along with a 6SN7 from my limited inventory of spares because they omitted a replacement tube from the repair package. The only other problem I observed was when one of the stock 12AU7s died about two weeks later and was replaced. There were no additional failures over the following three months. There were no negative impacts to the MP-3's reliability resulting from any of the tubes I installed or tweaks I applied, which suggests a generally stable design.

I was a field engineer for a good number of years with a Fortune 10 medical equipment manufacturer, have seen uncounted hundreds of printed circuit boards, and repaired quite a few of them to ISO standards. Of course, I examined the guts of the MP3 while I was replacing the burned resistor, and was very surprised to see a wide variety in the quality of solder joints. Most were perfect or close to it. On the other hand, there were several others that looked amateurish, as if the soldering iron wasn’t large or hot enough to make the solder flow properly. All of the point-to-point wiring was very neat and professional looking.

My primary source is analog (Kuzma Stabi Reference, SME V, Graham 2.2, Koetsu Urushi and Rosewood Signature Platinum), so the performance of the phono section is critical to me. After a few hours to let the new, stock Chinese 12AT7s settle in, it was very clear that these tubes, well, should be replaced with tubes of your choice. Soon. The sound with the stock 12AT7 (phono stage) tubes was quite harsh and two-dimensional. Very "solid state". A friend who listened to this MP-3 remarked that it sounded like the MP3s he downloads from the Internet. After the initial posting of this review, one MP3 owner wrote to me, "I have seen your comments about the MP3 and pretty much agree that out of the box it sucks." So the first order of business is tube-rolling. If you wonder why that is necessary for a component that costs almost $4000, you are not alone.

Normally, products are reviewed without any tweaks or changes. But in the case of Atma-sphere, the factory often recommends changing tubes, and there are many posts on the (now closed) Atma-sphere Owner's Group Web site regarding changing tubes. This review could easily end at this point with the Overall Rating below, but since tube rolling is "factory approved", it seemed reasonable to do this for the purpose of discovering the potential performance of this preamp. I won’t mention exactly which tubes I ended up using, because depending on your point of view, they are either wonderful or mediocre sounding tubes. Some were quite expensive, though. Let’s just say that further tube changes resulted in a different sound, but not an improvement in sound over the combination I settled on using. The substitutes were a vast improvement over the stock 12AT7s and transformed the sound of the MP-3. The four line-section tubes, two 12AU7 and two 6SN7, sounded fine and were not "rolled", other than replacing the two that failed.

Let’s talk about the sound. As I configured it, the MP3 is a very dynamic preamp with full, powerful, deep bass. It throws a wide and very deep soundstage. With small ensemble music, it is simple to pinpoint the few instruments presented. A cappella and solo vocals are presented with lifelike, believable, 3-dimensional, pinpoint precision, with excellent layering towards the rear of the sound stage. You might never hear a better reproduction of a well-recorded, solo female voice. The sound from bottom to top is full and very resonant and rich, but without any hint of a caramel syrup flavored haze. On the contrary, there is often startling snap and crispness, but only when the music demands it. When many musicians are present, their individual images blend together around the edges making it more difficult to identify the precise placement of each individual musician.

There is a very entrancing midrange and it displays a huge range of deep, fully saturated tonal colors, never sounding flat or processed. Poor recordings don’t sound quite as bad as they could, but good recordings can sound really wonderful and completely involving. The relationship between an instrument’s fundamental tones and its harmonics is presented in a natural and believable manner. This is a relatively uncommon trait, but one that is required in any great component. The Teflon capacitors made a large improvement in the transparency of the midrange and high frequencies and are easily recommended, so much so, in fact, that they should be considered standard equipment. They help the MP-3’s already good midrange improve to become some of the best in the business. The two Koetsu cartridges used during the review period certainly helped with this impression. You will have to be in a fairly rotten mood for this preamp to not draw you in and hold your attention until the lead out groove.

Late in the game, some top preamps from Ayre and Rowland passed through the system, and the comparisons were very illuminating. The midrange on any of these preamps was very natural, completely grain-free, and 3-dimensional. Comparing the MP-3 to the Ayre K3x and Rowland Synergy IIi with Cadence phono stage (which also uses Jensen MC transformers), preamps that are often regarded as some of the best of the genre, was exactly like comparing a Koetsu Rosewood Signature cartridge to a Rosewood Signature Platinum. Exactly. The Rosewood Signature is looser in the bass, making it difficult at times to follow individual bass lines, and has a treble range with lower resolution than its big brother that can make the very complex sound of cymbals sound more like white noise instead of clearly resolving the almost ephemeral shimmer of metal. The RS Platinum has completely clear and highly resolved treble – that same cymbal is scarily real - and tight and easy to follow bass. This analogy summarizes the MP3's character very well, and offers a good idea of the analytical abilities of this preamp. The bass and lower midrange of the MP-3 had a fuller, more prominent sound than either of the other preamps. All three preamps have balanced phono inputs.

I also had the opportunity to compare the stock MP-3 to the $2500 remote-controlled Audio Research SP16. The MP-3 had a warmer, more full bodied sound which complements the M60 amplifier's very slightly lean character very well. The SP16 was much quieter, had leaner (more accurate) but easier to follow bass - tighter, not as much bloom, slightly greater resolution in the treble, and greater delineation of individual instruments during complex music. The MP3 won out for simpler works, as noted above. The build quality of the SP16 was excellent, as you would expect from Audio Research, and far superior to the MP3. For example, when I was reinstalling the top cover in the MP-3 after replacing the burned resistor and failed tubes, I had to insert an XLR connector into one of the jacks on the rear panel and push down to bend the rear panel out slightly so the holes in the rear panel would line up with the holes in the top and the screws could be reinstalled.

Maybe it’s just me, but I don’t like noisy components. In fact, with the state of current technology, I see no reason why we should have to deal with them at all. If the noise of any component is above the surface noise of a clean LP as heard from the listening seat, it adds an audible level of “distortion” and detracts from the amount of enjoyment I get from recorded music. While the MP3’s line stage is very quiet, the phono stage was not. Any volume control setting above 12 o’clock, with or without the Cascode Mod (which substantially reduces noise, but also reduces gain and therefore requires higher volume control settings), resulted in too much noise for me. With the stock tubes, no step-up transformers, and without the Cascode mod (a stock MP-3 that you would buy for $3800), I was using the volume control at 3:00 with the Koetsu RS Platinum cartridge. At this setting, I measured an increase in background noise at the listening seat of 16 dB (C weighted) greater than the background noise of the system with the volume control fully off. That is a lot of noise, my friends. Again, this was from the stock MP3 with factory supplied tubes and no step-up transformers. With either the Ayre or Rowland preamps, noise was not an issue at all.

This intrusive level of noise was the impetus to add the Jensen 347 step-up transformers, and why the transformers are now offered as factory-installed options. The transformers did exactly what I wanted them to do: provide gain with no added noise, distortion, or artifacts. They excelled at this, and provided either 12x or 24x of invisible gain. In fact, there was a small but noticeable improvement in the sound of moving coil cartridges when feeding these remarkable transformers. An added sense of ease was obvious, making the presentation just a bit more tangible and believable. And it makes sense: the coils in the cartridge feeding the coils of the transformers which results in a closed circuit of just wire. Very Zen.

“Gain with no pain” provides a succinct but accurate statement of the effect of these Jensen transformers. They are available directly from Jensen Transformers for your own projects, too. I had been in contact with Jensen for many weeks before the 347 was released, and was always impressed with their product knowledge, willingness to answer my questions, and the amount of effort they willingly expended to make sure that the transformers were accompanied by exactly the right parts to work perfectly with my cartridge and with the MP-3. I have never experienced better customer support than I enjoyed from Jensen Transformers. Thank you once again, Dale! I hope you sell a semi-trailer full of 347s to a lot of lucky audiophiles.

I tried a 0.6 mv cartridge and a 0.2 mv cartridge, with the transformers wired at both 12x gain and 24x gain, with and without the Cascode mod (the preamp definitely sounds more transparent with the mod). With the step-up transformers, but configured with the Cascode mod which results in lower phono stage gain, noise was always an issue in my system (with stock tubes or others) with either cartridge since the volume control was above 12 o’clock. Different preamps and amps were substituted in an attempt to identify a system compatibility issue which might cause the excessive noise, but the one common factor was the MP-3. On the other hand, others have reported that noise is not a problem at all in their systems. Towards the end of the review period, the factory mentioned that they could get rid of the noise if I returned the preamp again, but since I had purchased this unit and felt I had a solid understanding of its overall strengths and weaknesses, I decided not to pursue any further changes.

Different power cords had a huge effect on the sound of this preamp. This is an effect that usually indicates a poorly designed power supply, one formulated in the lab but unable to deal effectively with real-world power problems. The cords showed their individual character just as if a treble control was available – from dull to bright with the change of a plug. Sorbothane feet were used under the MP-3 to good effect. I also used those red silicon O ring tube dampers. They helped reduce microphonics significantly, since even a gentle tapping on the top of the preamp was heard very clearly through the speakers with the stock tubes and others. Three damper rings on the rear (input) tubes, two rings on the forward phono tubes, and one ring on each of the 12AU7s offered a noticeable upgrade.

There is one lesson I learned from this unit. It is much easier to like a component that leaves out some part of the musical message rather than a component that adds some information of its own, as the MP3 can. So much depends on the tubes used and other factors that it would be a big challenge to know for certain how good this preamp can possibly sound, or even how it might perform for you. This is why I have included so much detail about my experiences living for six months with the MP-3. However, if you love to upgrade and tweak, you'll have a ball with the MP-3. I just want to listen to music. So here is an important notice: YMMV, so much so that your impressions may differ greatly from mine. Bon Voyage!

One could expect the extensive option list to negatively affect resale values because when you buy a used component, you enjoy a proportionally lower selling price than you would pay for a new component. However, upgrades are at list prices, plus shipping. So your initial purchase price of a used MP-3 may need to be lower than normal to make up for the full-priced upgrades a particular MP3 might need to meet your requirements.

The MP-3 is a preamp with so many important options and system dependencies that a definitive review is almost impossible. I don’t know if it would be economically similar for a specialty audio manufacturer, but major car makers found it was cheaper just to give everyone electric windows and A/C for a modest up-charge. And friends, Audiogon haggling-over-price aside, if you can drop four big ones for a preamp, you will find a way to swing one or even two more if you are convinced it will sound significantly better.

Which upgrades and modifications are in a particular MP3, which tubes are installed, what cartridge is used, etc., will all be determining factors for you to decide if this is a "must have" good preamp or a just an average one that says, “keep looking”. This unit is almost $7000 loaded, plus the cost of your choice of tubes and tweaks. Considering its poor construction quality, high-failure rate, and lack of advanced features, the MP-3 faces serious competition in today's preamplifier marketplace. Even though this particular evaluation is finally done, I suspect a comprehensive review of this preamp in final form will not be available for some time to come.

In summary, when everything is just right, the MP-3 can be very entertaining on most music. The following rating reflects the basic MP-3, no upgrades or tweaks, and stock tubes.

Overall Rating: 3 LPs (out of 10)

UPDATE. August, 2006. In a response to a comment that I posted on a message board, Atma-sphere agreed that under certain conditions, the MP-3 preamp "might have come off as noisy". In addition to directly validating the observations in this review regarding noise, the factory implies that system matching, especially regarding gain, should be carefully evaluated prior to purchase.

UPDATE. January, 2007. There have been several posts on a public audio message board from one or more interested parties that contain personal and defamatory attacks against this writer. I have tried repeatedly to respond to these posts for the purpose of defending myself and also the fairness and accuracy of this review. These responses are routinely deleted from the message board within minutes of being posted. I ask that you please keep in mind that my apparent lack of response to posts in other venues is not an admission that the information in these posts, in whole or in part, has any validity and/or truth whatsoever.

Since this review appeared, I have received several alarming emails from owners and prospective owners who called the factory, mentioned points raised in this review, and received information that does not accurately reflect the facts of this review or associated events and conversations. Please engage your brain when evaluating this information. In the words of Deep Throat, "Follow the money".