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.
