OTL amplifiers were inspired by the passion for producing great sound but without the transformer. Whether you are an audiophile who understands sound or simply someone who knows what they like, then systems designed with OTL amps by Atma-sphere are certain to tick all the right boxes.

What discerning listeners understand is that unlike the mass production market, high end systems are not about money, but quality.

About Atma-Sphere

High-end audio is about devotion to design and a desire to make the intensity of sound as good as it can possibly be. OTL amplifiers by Atma-Sphere have been achieving those objectives for over 40 years providing some of the best in the music industry with what they need and love – quality audio.


MA-1 Amplifier

M-60 Amplifier

MA-2 Amplifier

ma-1 amplifier

Recipient of The Absolute Sound’s prestigious “Golden Ear Award” in 2000, the MA-1 enjoys an enviable reputation. Now the Mk. 3.3 series builds on proven technology. An improved output section and enhanced driver circuit contribute to superior low-level detail, smoother sound, wider bandwidth and AC power immunity. The rugged, non-magnetic chassis features classic looks with superior layout. Setup of the amplifier is simple with it’s automatic biasing system. The controls and switches are ergonomic without sacrificing performance. 

The MA-1 is extraordinary in every way. Not only is normal operation easy on the vacuum tubes, the effect of a tube failure on the unit is entirely inconsequential. Despite its extreme performance, the MA-1 is known for remarkable ease of setup, ease of operation, day-to-day consistency and of course extreme musicality. 

Pre Amplifiers

MP-1 Pre-amplifier

MP-3 Pre-Amplifier

mp-1 pre-aMPLIFIER

In 1989, the first MP-1 introduced balanced line technology to the world of high end audio. It was the first balanced, fully-differential preamp ever made, with innovations that were breakthroughs at the time and remain so today. With decades of refinement, patents and awards, the MP-1 is a paragon of the audio world. 

The Mk. 3.3 update has affected the MP-1 more than than the rest of our lineup. More about that later… if the MP-1 is something you’ve not encountered before, it is unique in the world of preamplifiers. It easily outperforms conventional line stages and any passive or transformer volume control on account of its patented direct-coupled output which allows for greater transparency while also preventing coloration from interconnect cables. With only three stages of gain in the entire preamp (including the phono section), our Balanced Differential Design® is an elegant signal path that assures low distortion, wide bandwidth and dynamic range. No matter what you thought was the best, the MP-1 is an audible improvement. 

OTL Amplifiers

UV1(Pre-Amplifier & Headphone Amplifier)




The S-30 is the unchallenged state-of-the-art in low power vacuum tube amplifiers. With its simplicity of operation, small footprint, and all the features of our larger amps, the S-30 represents the high-water mark of compact OTL design. 

For those who seek the ultimate in amplifier design the S-30 gives you the same precision and sound quality for which Atma-Sphere is known. Featuring automatic bias and a large VU meter, operation is elegantly simple. 

Ralph Karsten

Founder & Owner

The audio components designed and produced by Atma-Sphere Music Systems are considered by many authorities within high end sound industries as being world class in every sense! So, in our continued commitment to bringing clients only the very best that money can buy, Phantom-Audio have also brought on-board, Ralph Karsten, the founder and owner of Atma-sphere. His company is small, yet world renown for its quality and innovations, and has been designing hand-crafted, unique and award winning amplifiers since 1976 which provide audio connoisseurs with the very best that high-end audio has to offer.

When it comes to firsts there can be little doubt that Ralph Karsten and his designers have been at the front on many occasions. They were the first company to design, patent and produce 100 percent reliable Output Transformerless (OTL) amplifiers and went on to design the first balanced OTL. They are also the world’s oldest producers of triode amplifiers and manufactured the first fully differential zero feedback tube amplifier.

And, if it’s power you are looking for, then Ralph Karsten has a first here too: the MA-3 produces over 500 watts into 3 ohms and is the most powerful OTL ever made.

Atma-Sphere also have quite a few firsts when it comes to preamps and, not least, in producing the world’s first all-tube preamp with a direct-coupled balanced output.

So, when it comes to manufacturing, no matter which system you purchase, know that Ralph Karsten and his team will provide you with the best. Each component is individually selected enabling production of made-to-order and hand-crafted units designed not only to last two decades, but which will ultimately provide you with an enhanced audio experience which has to be heard to be believed.

There is, in truth, no better amplifiers on the planet than those designed by Ralph Karsten, which is exemplified by the fact that, since the 1950s, only three patents have been issued to OTL manufacturers – and two of those were to Atma-Sphere.

OTL amplifiers are noted as being the most transparent of circuit designs. What this means in reality is that both noise and distortion are practically eliminated and what you are left with is the most natural, and unforgettable music, imaginable. These designs have led Ralph to attract a cult following of the most discerning listeners who appreciate the technical contribution that he has made to audio throughout his career.

If you are looking for audio which is beyond anything you have heard before, then look no further than components which have been designed by Ralph Karsten; a man driven to bring you the best quality sound experience possible.

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