Atma-Sphere MA 2s for Dummies (by a dummy)


After a 9 month wait (covid) I finally received my MA 2s. Because these amps were going to be located in the shop under the loudspeakers I asked (demanded?) for trigger inputs. Ralph Karstens agreed to do this and did not charge me an extra cent for it. More on this later. Ralph warned me up front that the 6AS7 driver tubes were going to be problematic for a while and he was not kidding. I got the amp with 40 Chinese 6AS7s and rapidly started blowing tubes. The trigger on one amp did not work. Ralph warrantees the tubes and immediately sent me new ones. With the amps I also ordered a full  set of tubes to have on hand and Ralph promised the Russian versions which most people think are better. Ralph felt the bad trigger was due to one of two relay boards. He was game to let me change it out and sent me two new ones just in case. I installed it and both triggers have worked perfectly since. The reason it was two relay boards and not one is because the first trigger lights the filaments immediately and the timed 2nd relay turns on the B+ 30 seconds later.  When I had the amp apart I took a picture of the construct which I encourage you to see on my system page. These amps are totally hand wired, point to point and are an electronic work of art. The board that failed was at the bottom between the inputs right in the center. Tubes may fail but not these amps they are rugged and will last eons. 

The amps were running fine for over a week and I was busy adjusting to them when the Russian tubes arrived. I pulled all the Chinese tubes and installed the Russian ones. As per Ralph's instructions I let the tubes run on filaments only for 6 hours and was going to play them lightly for several days before rocking out. I put on Analog Productions 45 RPM copy of Waltz for Debby and was floored by the sound. The Sound Labs were more energetic with the MA 2s, a lot more energetic. About midway through the second side there was a pop in the right channel and I knew I had lost a tube. I went downstairs climbed a ladder and looked over the face plate to see that one tube all the way in the back was dark. This was VERY unusual. When these tubes blow they burn out their fuse links only and the filaments continue to run. To find the bad tube you have to pull each tube and inspect the fuse links which are hard to see. This one tube had really torched itself. The inside of the tube had a large black ring and the getter had turned white. I installed a new, broken in tube and returned to Walt for Debby. In 10 seconds there was a very loud sizzle then pop and the amp went dead. Now I was really worried. You can blow 3 or 4 tubes at least and the amp will keep running. Something bad had happened. The post mortem exam revealed 3 bad 6AS7s and the two 6NS7 driver tubes had blown. This hardly ever happens. I sent Ralph a picture of the black tube and he was amazed. He knows these amps backwards and forwards. This was a rare event. We hypothesized that the black tube had somehow weakened the driver tubes and they failed the next time they were run taking out three more weak 6AS7s. I did not have any extra 6NS7s so the system was down for a few days. The moral of the story is the Russian tubes are no more reliable than the Chinese tubes. The problem with 6AS7s is that the element is supported only at the top of the tube. At the bottom it is just hanging in the vacuum. If you drop one just right the entire element goes crooked ripping the connections at the bottom. They ship poorly. About one in twenty are "wonky" when you get them another two will blow their fuse links indicating a short within the element. 

Ralph assured me that the amps were ok and sent me 10 more 6AS7s and a full set of 12 NOS Russian 6NS7s that were obviously better constructed than the new JJ tubes the amp came with. I kept JJs in the driver positions and put four NOS tubes in the voltage multiplier sockets of each amp. These are the tubes that "voice" the amp. Since then I have blown one tube in the left amp and that is it. The amps have been trouble free since. One night I had an old musician friend over, a real rocker and we spent two hours at 95 dB and I did not lose one link. Ralph knows his amps and his support is second to none. 

80% of MA 2s are being used on Sound Lab speakers for good reason. The impedance of ESLs increases as you go down in frequency from 1 ohm at 20 kHz to 30 ohms at 20 Hz. Normal amps lose power into an impedance that high where you need it most. The MA 2s do not. They put out 220 watts regardless of impedance. The result is that first you have to turn the brilliance control of the SLs all the way up and turn the bass control all the way down. Measuring this revealed a very flat curve from 120 Hz to 10kHz with a slight downward slope to 20 kHz which was down 4 dB. This is great for louder listening. I cross to subwoofers at 120 Hz currently. The increase in the power of percussion produces frisson. The buzz in bass strings is more evident. Little details are more obvious. I should also mention that the amps are dead quiet. The midrange, as others have noted, is in a class by itself. I cannot find adequate words to describe it. The high frequencies are as good as any class A  amp I have heard. I can not comment on the bass below 120 Hz. Others with SLs have not liked it and they have switched to SS amps. I personally think this is a characteristic of the SLs which do not like making low bass. The SS amps have so little power down there they are not exposing this problem. From about 100 Hz up the SLs are brilliant. As a one way driver the cohesiveness of the music produced by SLs is a trait absent in multiway speakers. You have to hear it to understand it. For certain the MA 2s and SL speakers were made for each other. 

I forgot to mention, MA 2s get very HOT.

I should also mention that to please SS fans Atma-Spere is now making a class D amp that reportedly sounds like a tube amp. He is using a proprietary circuit, no modules. The amps have large linear power supplies and produce power like most class A amps. The price is also very reasonable. There is a review pending. 

128x128mijostyn

Nice review @mijostyn ,

I own the MA-1's and they are my winter amps for my Vandy Treo's.

Ralph is a stand up guy and as we can see from your experience, totally committed to providing top notch service.

I bought the Atma Class D amps, and trialed them for a few months. I took them to Audioconnection and had a 'shoot out' with other amps-mainly Belles. In short, we liked them, but they had a drop off in the upper frequencies that contributed to a bit of 'lack of life' to our ears. (We did hook them up to a pair of Maggies and they did sound pretty good). 

Mind you, I am an Atma lover, but the Class D amps just seemed to lack that bit of 'sparkle' that Class A or AB amps can have. I probably should have contacted Ralph, but wanted to move on. 

The Class D amps did sound very, very good. Excellent bass control, and overall even sound, but they just lacked that bit of upper frequency 'sparkle'. Perhaps the word 'engaging' would be more correct. I should also mention that we were listening to Vandersteen Treo's, so YMMV.

Bob

@Mijo I bought a pair of M60s new 23 years ago and still own them and have never once thought of making a change. Other than upgrades, they have never had a service issue. About 15 years ago I bought a second pair (used) as they were on the elongated chassis that AS used for a short time for M60s as those chassis better fit into the space I have available to me. These amps have never required a repair. Naturally, along the way, I have experienced some power tube failures, but nothing at all dramatic like you did early on. But I would like to say in my overall experience that you will find the Russian 6AS7s to be the heartier and longer lived tubes. A friend of mine with MA-1s and I, starting about seven or eight years ago, began sourcing all of our 6AS7s from ebay sellers in Russia. These are all military (I’m sure) pulls but they measure strong (using a Hickok 532) and have exhibited no tendencies to early failure and such. Last time we bought they were running about $5. per tube in lots of 25 or so. I’m tubed up for now but if the day should come when I need a new supply, ebay will be my first stop.

 

@gdnrbob

I bought the Atma Class D amps, and trialed them for a few months. I took them to Audioconnection and had a ’shoot out’ with other amps-mainly Belles. In short, we liked them, but they had a drop off in the upper frequencies that contributed to a bit of ’lack of life’ to our ears. (We did hook them up to a pair of Maggies and they did sound pretty good).

Mind you, I am an Atma lover, but the Class D amps just seemed to lack that bit of ’sparkle’ that Class A orAB amps can have.

Based on prior posts here I know that you have much appreciation and admiration for Atma-Sphere products. Your comments are candid. I can imagine that the MA-1 mono blocks are splendid with your Vandersteen speakers and set a very high reference point. I can understand how you preferred them to the sibling class D amplifiers In your specific situation. It’s simply personal preference for each individual listener.

Charles

Thank you very much for your post. Really interesting. I love Sound Lab speakers. Powering them can be challenging. My hat off to you and Ralph for pushing the cutting edge. You have a beautiful system, it must sound incredible.

Since my system has always been at the very edge of my financial capability, complete reliability has been at the forefront of my mind. This kept me out of tube amps for thirty five years… which I am sorry. Happily I have gone the Audio Research route and have had complete reliability in tubes… I have replaced two on schedule among the 40 I use after 3,000 hours. 
 

I completely understand what you are doing and respect the collaboration going on between you and Ralph. I imagine you have a truly amazing sounding system.

@ghdprentice , My audiophile brain is never entirely happy with the results. Improving, no question. Could be better, I think so. Lewm has suggested changing the high frequency transformers for full range ones running them in parallel with the bass transformers. I have Serbian Toriods coming and am going to try this approach. I have four new subwoofers under construction almost finished using eight 12" drivers in very unique enclosures. Ralph has suggested biamping the transformers, another consideration. I will be testing the Beta program for the new DEQX Pre 8 processor shortly. I wandered into that role accidently by making myself a PITA. The people testing are supposed to get their units at a discounts. Suites me. After all, this is a hobby. When does a stamp collector stop collecting stamps.