We live in a time of quick and instantaneous gratification, from fast food to fast technology. Although important at the moment, most of the things we seek are just as quick to have little or no meaning to us. Today's hot computers that we lust over, are tomorrows hunks of junk that we can't get rid of fast enough. Computers are just that way, due in part too accelerated capabilities, and also due too what we expect of them. Much of what we acquire on life now is headed in the same direction - and that includes an awful lot of high-end audio gear.
In the world of audio the reason for much of our dissatisfaction is that we don't often take the time and effort to buy or build anything of genuine intrinsic value. Many of us have never actually built any audio gear, and so we have little appreciation of what's involved. Even worse when looking for a building experience with true value, rarely do we find anyone offering a high quality product sold as a kit that gives its owner the challenge and gratification of making it all happen, something that, with care, will outlast its owner and creator. It is rare in our culture to hear the proclamation: "I made this myself." It is therefore refreshing too find something that defies the norm.
Welcome the Atma-Sphere M-60 MKII Balanced Differential Amplifier
This amplifier is offered by its designer, Ralph Karsten, as a moderately challenging kit, or as a factory-wired amplifier. It is not a simple single-ended design; rather it takes the owner in the direction of advanced audio construction and design. This is the real thing folks; here are the specifications for those who want that up front:
Dual Monoblocks
60 watts/channel into 8 ohm load/45 watts into 4 ohm load
Power bandwidth: 2 Hz - 75 kHz within 1/2 dB
Frequency response (1 watt): 1 Hz - 200 kHz within 1/2 dB (-3db @ 1.5 MHz)
Phase shift: less than 1 degree @ 20 kHz
Power supply storage: 140 Joules/chassis
Output section risetime: 600 V/micro-second
Feedback: 0-3 dB, hardwired selectable
Power consumption: 300 watts/chassis
Tube complement: 8 6A57/channel and 4 6SN7s
Weight: 30 lbs./chassis
This is a serious amplifier. Building it requires paying attention to what you are doing following the instruction manual with alertness is important and you must know how to solder well. However, the instructions do not assume that the builder is an EE, or that you have the skill of translating electrical schematics directly. The instructions use pictographic drawings of the different stages of construction and a photographic image of the inside of the amplifier. There is a simplified schematic included as well, though it is not a complete schematic of all of the amplifier circuitry.
The instructions include some general construction tips, but I found them to be a little weak on this point. I had a very early version of the instructions; while working on the kit, Atma-Sphere sent two other versions to me that contained changes to the instruction set. The manual has been a "work in progress," and I would expect that it will continue to evolve, becoming ever easier to comprehend. Use logic and forethought and you will succeed.
Before starting to build this project read the manual carefully. As in all vacuum tube amplifiers, there are lethal voltages present inside the chassis. One of the features most different in this design is that there are no audio output transformers, and there are no circuit boards. It is hard wired completely. Both are a huge advantage to the quality of the sound. Circuit boards in tube equipment are there as a manufacturing and cost cutting convenience, but diminish the ultimate sound reproducing capabilities. As an OTL (Output TransformerLess) design, it completely eliminates the need for output transformers, and that is one of the reasons for both the high speed and high bandwidth of this amplifier.
The parts quality is very good - commercial grade or custom manufactured - and is designed for durable long-term use. Once built, the amplifier is rugged. It has the look of late '50s instrumentation, complete with a fine meter in the middle of the power supply transformer housing cover. The purpose of the meter is setting the DC offset and bias. Once adjusted. the meter section is out of the signal path and sits dormant until needed again. This meter also looks great. The kit comes with solder and sufficient lengths of different types of wire for specific applications in the kit.
Concerning wire, I should point out that we at JENA LABS do design and manufacture some very fine interconnects and wire. Our hook up wire is made to exacting specifications, designed for super neutrality, high current capability and high bandwidth. Given the truly high performance capabilities of this kit, we believed that we would be remiss if we did not advance the Atma-Sphere kit to the limit of its design threshold by not using our best hook up wire. The same comments hold true for the solder developed by George Cardas of Cardas Audio. We feel his Cardas Quad Eutectic Solder is without peer. So, JENA LABS wire and Cardas solder were used. Jennifer and I resisted the temptation to make circuit changes or substitute other parts. This would allow us to create an honest review sample, and although changing wire types will affect sound; it will not make a bad amplifier design sound good. Nothing can do that.
The kit comes with all of the tubes used in this amplifier, including 4 spare 6AS7 tubes for the output section. The availability of both tube types is legion, have no fear, and they are very available. The 6AS7 power tubes are currently manufactured by at least two big and famous tube manufacturers: Sovtek (provided) and Svetlana. They are often used in power regulation circuits, and are ideal for the use in output transformer-less designs such as this. Because they arc currently made in large volume, they are relatively inexpensive. between 15 and 25 dollars each. The 6SN7 driver tubes are one of the most common tubes ever created. At one time almost all tube companies made them, and they number in the millions. Those provided in the kit are JAN (Joint Army Navy) Phillips/ECG 6SN7WGTA, and are superior io grade to many other ones available. I suspect that these were made in the mid 1980's, and are of US manufacture.
When we got the Atma-Sphere amplifiers in for review as a kit, I became enthusiastic for two reasons. First, I love to build amplifiers as a functional art form, second these were not a common design. My wife Jennifer is one of the great audio designers of the world; she has been re-educating me in advanced differential audio amplifier design for some time now. When a variant of this design theory arrived, I was really delighted. Even though this design by Ralph Karsten is not the final word in amplifiers - what is? - nor was it meant to be so, it definitely falls into the category of an advanced balanced differential type. This is a well thought out and well executed entry point in this type of design. Ralph can and does build designs that are much more advanced than this, but they are far more expensive and much more complicated.
Well, you ask, what did I think of them once they were built? A check of voltage specs is step one. The Atma-Spheres turned out to be within specified tolerances without any adjustment. Tubes were then installed and operating points once again checked. Everything was well within spec. Following the instructions had yielded a proper build. Ralph warned me to expect less than super sound during the break-in period, and that is what I got. At first the M-60 MKII's sounded very, very grainy.
No problem; it was expected. We were advised to break them in at least 60 to 80 hours before passing any judgment. Capacitors, transformers, tubes - everything in performance audio must be broken in before an accurate appraisal of sound quality can be fairly made.
So we waited, and guess what we got? WOW! These amplifiers are very fine. Not just "acceptable." Not just "satisfying." They are great! Jennifer and I hear a lot of audio equipment; we know what excellent audio is, and our listening system is very revealing. We tried the M-60 MKII amplifiers with our ultra-modified Acoustat 1+1 electrostatic speakers. We tried them with the Graybeard KB-2-2 speakers; we tried them with Merlin VSM-SE speakers. We tried different music sources: vinyl records, Digital CDs, analog and digital LaserDisc audio, and even original analog master tapes on our pro Ampex rigs. On and on; we tested and listened. The amplifier in all cases provided exceptional performance for its rated power. It proved beautifully transparent and natural with cone speakers. Even with the torturous load imposed by electrostatic speakers, they sounded great up to the limits of this amplifier's power capabilities. Gilbert Yeung's Blue Circle BC-2 monoblocks drive the 'stats louder, largely due to their immense output current reserve; the M-60s reigned supreme in transparency and resolution, but only at the softer loudness levels.
The sound of the M-60 MKII's is very transparent and very fast. The sound stage is wide, deep, and very clean - easy to listen into. With most speakers, the amplifiers are capable of very deep bass without loss of control. They provide very neutral and accurate sound all through the audible spectrum. If the music contained complex harmonics, these amplifiers provided accurate reproduction without adding any harmonic textures of their own.
We liked the amps so much that when the "Vacuum State of the Art Conference" was held a few months ago, we wanted these M-60 MKII Atma-Sphere amplifiers for use at the Show. Atma-Sphere Music Systems, Graybeard Audio speakers, and JENA LABS interconnects shared an exhibit room and produced very fine sound at show. We were pleased that Dick Olsher and Bascom King spent so much time enjoying music with us. We think Dick said it well when he commented that our room was a musical haven from the din and roar of the show.
One final note: The M-60 MKII's have three separate, generously sized transformers in the power supply. Most audio equipment with large power transformers will hum, yet these amplifiers are silent. I did not expect this. It was almost spooky when I noticed the silence behind the music. Buy them, build them, and enjoy.
M-60 MkII kit, pair $2,295.00 plus shipping
Round Meter upgrade $250.00 (Rectangular meter standard)
Parts Upgrade, Inquire for current availability and price.
Built up amp, pair $3,795.00
Jennifer notes. . .
Atma-Sphere does have some upgrade parts that can be ordered with your kit or built up amp, at extra cost. They also guarantee that if you buy the kit, you WILL end up with an operating pair of amps. If you find the kit is just too much for you they will finish the build and ship you back your tested and operational amps. As of press time, 55 kits have now been sold. Of those, only five required factory help. All of those five purchasers had never done any electronics project before. Of the remaining 50, all the buyers had previous soldering skills, and knew their way around a screwdriver and pliers. Most have been successfully completed; the remainder, the most recently sold, are still giving their builder the joy of construction. How's that for assurance?
Next time. . .
. . . we'll dive into that Taddeo Digital Antidode II, unleashing some easy and musically effective mods. I'm also going to share with you some really interesting recordings that have recently come my way. Until then. . . AUDIOs!
Designers/Manufacturers
Quantum Speaker Filter
Bybee Technologies
408-257-0961
Merlin VSM-SE
Merlin Music Systems
P.O. Box 146
Hemlock, NY 14466
716-367-2390
T100SB Monoblocks
KORA Elecronic Concept
c/o O.S. Services, Randy Bankert
818-760-0692
Ovation
NOVA USA
409-696-0723
e-mail info@novausa.com
Svetlana Electron Devices Marketing and Engineering
3000 Alpine Road
Portola Valley, CA 94028
415-233-0429
M60 Mk.II
Atma-Sphere Music Systems
612-690-2246