"What is the star ground circuit?
A star ground circuit is a technique for preventing ground loops. Each ground connection has its own wire that connects to the central ground of the amplifier. This helps prevent added noise and hum problems and it helps the amplifier to sound better.
How have you perfected the OTL circuit from your earlier models?
Actually, it is safe to say that the OTL circuit I devised has spent more time working on me than me on it! It has taught me how to build a better driver circuit and which components and techniques are important to getting the sound right, and which ones aren't. The actual
output circuit has not changed at all since I built the first one. Instead, it has undergone a series of refinements. Most of that has occurred in the driver circuitry. At the time, tube driver circuits in general were not up to the task of driving the output section properly. They had too many flaws. As transparent and demanding as the output section has been, it placed huge demands on us to get what's preceding it right. The current iteration of our OTLs feature driver supply regulation and easier setup and use (including switchable Class A/AB operation). The lack of noise in the power supplies has really helped out the amps in the last few years in particular. We have also made them very quiet so even the most sensitive hornspeakers can be used.
The amps I am reviewing are not self biasing, but I understand the latest models are. Can you explain how that works? Do you still employ a standby switch ?
The standby switch is a huge convenience, so yes, we still use it. Over the years, we have developed techniques for biasing Circlotron amplifier, and that is covered in our patents. The latest patent, which we initially used in the preamps, also has applications in the amplifiers and has led to the automatic bias setup. You still have to adjust the DC offset. It's not entirely automatic but means that the amp now has only one adjustment for 14 power tubes. The easier we can make it, the less likely it will be that someone can set it up wrong.
How do you feel your OTLs are superior to other brands on the market?
Well, to start with, some of the other OTLs on the market are using a circuit that I designed and published in Positive Feedback magazine back in the early 90s. It was a circuit that I had abandoned some years before for a reason and I now hear that reason in those competitor's amps. So they are where we were in 1985. That puts us almost two decades ahead of our strongest OTL competitors. To this day, we still produce the most reliable OTLs, which are as reliable as any tube amp made. I can't reveal why that is so since that is proprietary but I can say that this reliability also gives us greater accuracy and transparency than our competition.
Who is the ideal customer for the MA-1 MkII.3?
Uh... someone who likes music? For all its features like Class A operation, all-triode, patented OTL circuit etc., the amplifiers are intended to be easy to live with. My original vision of 27 years ago, which I still stand behind, is that you don't have to be a special audiophile golden-ear type to really appreciate what these amplifiers do.
Do you recommend that certain components such as preamps or speakers with certain specs be used to get the best results with the amps?
Absolutely. It's easy to show how all amplifiers do not drive all speakers properly no matter what kind of speaker you have. This is true of both transistor and tube amps. Tube amps in general prefer 8-ohm speakers to 4-ohm speakers, all things being equal and regardless of the type of tube amplifier technology involved. So you certainly do have to be careful if you want to serve your tube amplifier investment properly.

A good preamp is essential to showing what the amplifier (and system) can do - which of course is to serve the music. This cannot always be done with a passive system as one of the tasks of a line stage is that of interconnect cable control. Passive systems in general don't do this, which is why the volume control setting on a passive system has such a dramatic effect on the sound quality (ideally, the sound quality of course should not change with the volume setting). The MA-1 is quite revealing but it cannot replace what the preamp may have lost. That's why we were forced to offer our own preamps as well.
How does the MA1 MkII.3 differ from the previous model of this amp?
The new MA-1 Silver Edition differs from the previous MA-1 MkII.2 in the following ways: It features an extra tube in the driver section for greater bandwidth and lower distortion; regulation in the driver power supply; switchable class A/AB operation; and easier setup due to the automatic bias circuit. Additionally, the chassis is now a single-piece welded and ground, polished non-magnetic stainless affair (and the inspiration for the concept of the 'Silver Edition' which coincides with the history of my company).

A lot of features have been added with only a minor price increase to $9,950.00/pair. However, this price will begin to increase in the next few months as the cost (especially of labor) to build the amplifier has become a bit higher, not including any of the added cost of parts and shipping that has occurred over the last year or two."

As stated earlier, finding the right cables to make the Atma-Spheres sing was no easy task. The Omega Mikros I normally prefer with my BAT VK-75 were completely inappropriate, lending the Atma-Spheres an exceedingly clean but tipped-up sound that highlighted the treble -- often making my ears hurt -- while leaving the rest of the frequency range intact but bleached out. Using a pair of Stealth Audio Cables ICs and speaker wires (which sell for roughly the same price as the fragile Omega Mikros) created a much fuller treble presentation and also fleshed out the midrange and deep bass (though they were a mite boomy at times but hey, I like that).

While I am complaining, let me note the incredible heat these amps produce. It will be reason enough for some to pass them by. As I walked around my small apartment, I could feel the heat hovering in the air like a creeping furnace. The living room where the Atma-Spheres sat had the wallpaper boiling. Luckily, it's been a cool summer here in Manhattan this year.

An area that has reportedly been improved is the amp's biasing controls. My review pair required a two-finger hold down of two toggle switches affecting bias and DC offset while one sets them to the correct meter readings. The idea is that you bias the amps in Class A. Via a switch, you can then operate them in Class A or A/B depending on your preferences. But the A/B settings aren't marked, and the one page manual doesn't clarify anything with a nice diagram or illustration. So, I jumped in head first, unknowingly biasing the suckers in Class A/B, then flipping the switch to presumably run them in Class A. All sounded well so I didn't fret. Then I began noticing a smoky smell like burning plastic. This went on for days. Finally, I saw smoke coming out of a wall socket. I quickly flipped the breaker and upon closer inspection of the socket, saw that the back of the wall plate had melted to black - like cigar ash. Needless to say, I finally called Karsten for assistance.