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"One of the company's owners, Jim Fairhead, made a mistake when connecting his preamp. He inadvertently put the maximum signal through the Tenors into his Tannoy Churchill speakers. The protection circuitry shut down so quickly that absolutely no damage was done. The protection circuitry was designed to be so fast that there can be no accident that would destroy a speaker. Obviously this cannot be tested on every speaker but we believe that we have one of the safest, if not the safest, amplifier made.

"If a MOSFET fails, it will go into instantaneous shutdown without any spurious current to the speakers because the transistors themselves are shutdown within 1ms. Our current limitation system will shut the amp down even before a fuse can blow! The amplifier will shrug off a dead short - absolutely no damage. You'll get a big spark and maybe a damaged connector but the amp and speaker will be safe."

What is HSI (Harmonic Spectral Integrity)?
I've spoken in the past of a transparent sound field that balloons out into the room, immersing the listener into the music and yes, the Tenors have this in spades. However, with the Tenors you get the ability to hear the inner structure and delicate overtones not present in the initial attack but buried far more deeply. Subtle layers within the soundstage float effortlessly and naturally in reverberant space. Ask François about this or almost any question concerning their design goals -- transparency, dynamics or the tonal purity -- and his answer always comes back to HSI (Harmonic Structural Integrity). It is their fundamental building block. It is the uniqueness of the Tenor sound and the result of Michel Vanden Broeck's lifelong research and development. It is also clouded in a cloak of proprietary secrecy, hence you're stuck with my layman's explanation.

Every note from every instrument contains both a primary note and secondary harmonics that in essence define the characteristic sound and timbre of that instrument. Why do reed instruments sound differently from each other? It's these fundamental, secondary and tertiary harmonics interweaving in a complex tapestry that define real music in real space and separate the tone, color and timbre of one instrument from another. Harmonics are a series of related simultaneous notes produced by a musical instrument. The nature of the initial vibration and the type of enclosure among other things determine the nature of the harmonics. The human hearing apparatus internally sums the initial attack along with the multiple harmonics into the single color or timbre recognized as the instrument or voice. The sum of the harmonics in some instruments produce a purer sound like a flute while others produce more complex sounds, such as a saxophone.

According to Tenor, typical manufacturers tend to measure their components statically - a specific music snapshot with the corresponding harmonics and distortions measured and analyzed. This is where Tenor differs. They claim that one secret to their sonic success is the ability to reproduce the dynamic nature of the instrument and its harmonic structure. Imagine a specific instrument reproducing a specific frequency and visualize a graph of the fundamental note and its various harmonics. It's an instant in time but not real music. As the music changes, the volume changes, the frequency changes, the tempo changes, the fundamental note and harmonics change dynamically to the next state and the process continues seamlessly. How well the component can track the dynamic changes from one note and instant to the next is key. The ability of the amp to react to a continuously changing set of harmonic structures is what Tenor believes to be the holy grail of amplification. The key to this dynamic behavior is locked in the brilliance of Michel Vanden Broeck's mind who combines theoretical analysis, unique circuit designs and specific measurements using Fast Fourier Transform Spectral Analysis. I asked François if he would share the underlying nature of the design and measurements relative to HSI. The answer was a polite but firm "No." Michel did say, "It is not possible to directly measure this [HSI] because you must measure it in real time and no equipment exists that can actually do this."

At first I wondered whether HSI was just another marketing catchphrase - one of those feel-good sets of buzzwords to get audiophiles excited and nodding with approval. Yet after meeting the owners and employees of Tenor and listening to their internal discussions, Harmonic Structural Integrity is not a buzzword for an advertising brochure; it is the fundamental premise of their design work. They profoundly believe that if you nail the purity of the original note with its harmonics, then dynamically and instantaneously track the changes and do it over a wide band, you've achieved greatness. They contend that in the real world the true sonic measure of an amplifier is not a static reading occurring at point 'A' or point 'B' but the combination of these two readings plus the amplifier's ability to move from point 'A' to point 'B'.

Although I certainly don't understand the underlying engineering, Tenor claims that HSI is the key to the transparency, vividness and tonal correctness of the music.

The Sound
I asked Michel to describe the design goals for the 350Ms. He claims an interesting mix of theory, a unique concept of distortion relative to human perception, their ubiquitous Harmonic Structural Integrity and most importantly, the sound. His goal was "... to be closer to real music - a live concert. I know that it is almost impossible to recreate due to the amount of power needed to imitate live music. So we focused on a few parameters - the dynamics and tonal characteristics. I wanted to create something that was as close as possible to reality and avoid the classic coloration trap that makes people say, oh yes, this one sounds like transistors and this one like tubes."

So where do we start? How about with a simple proclamation that the 350Ms are the best amps I have heard anywhere, anytime. Too subtle? Okay, specifics. For me, the ultimate measure of a component is the ability to allow the suspension of disbelief and become lost in the music. The 350Ms are eerily good in this respect. For those new to OTLs who assume a traditional modified tube sound, you will quickly realize that a good OTL sounds neither tube nor solid state. A well-designed OTL has a distinctive sonic signature with spectacular transparency and vivid 3D imaging. Yes, I'm a confirmed imaging freak. I lean towards that wonderfully detailed holographic soundstage. Yet you often walk a fine line that can wander between real and artificial. It's like turning up the sharpness control on a television. You get the illusion of more detail but in reality the finest details are obscured. I'm continuously aware of the sharpness analogy relative to audio. For me OTLs in general, and the 350Ms specifically, are naturally transparent, detailed with solid imaging. Add a total lack of grain plus a dead quiet background and you will begin to appreciate that we have something really special here.

The Tenors bring a remarkable top-to-bottom continuity, which I've often called the Kharma effect (the speaker, not the moral law of cause and effect) in tribute to what I believe is the most coherent, disappearing, seamless loudspeaker ever made. As a traditional amp moves from frequency A to frequency B, its tonal characteristics often change. Some emphasize certain frequencies or certain ranges. Others are weak in one area but strong in another. Yet real music in real space presents a seamless continuity when room boundaries and acoustics are neutral. The Tenors are the only amplifying devices I know of which do not change tonal colors, emphasis or resolution from the deepest bass through the highest treble. The high resolution without microscopic steps as the music flows from one note to the next makes other amps sound - um, how can I say this - well, digital.

Power and Authority
The Tenors scale effortlessly. Performances glide from micro to macro, from subtle to dynamic with no change in perspective or tonal structure. Again, this is closer to real music in real space than I've ever heard before, totally unforced and totally dynamic. The dynamic response in the individual shades of texture is stunningly real. Dense orchestrations scale and envelop you naturally as if you were sitting in a concert hall. Mahler's Symphony of a Thousand [Utah Symphony Orchestra, Vanguard VSD-71120] with literally a cast of 900 is as complex as it gets. This record tests the dynamic range and resolving power of any system. Yes, when the music demands it, we all want it loud. We want big dynamics but at the peak there is often a strain. It's not always pure yet we accept it because it is loud and therefore we say, it is dynamic. But as François states:

"With Tenor there is no peak cut-off, every instrument is livelier. In a blind test, compare a simple violin through Tenor and any other high-power solid-state amplifier. With typical amplifiers, two or three percent of violin music might be at peak. Compare the same violin music through Tenor with its lack of compression. The difference on that 3% of the music makes the violin sound far more dynamic and alive."

Tenor claims no dynamic compression and almost no possibility of clipping, a statement which in an attempt to save my hearing, I can neither confirm nor deny. "We set the protection very near to the clipping level - 1% distortion. There is no dynamic compression in any way but if you go so loud as to approach clipping, the protection kicks in. There are a few other amplifiers that are more powerful and will not clip. But they will simply compress. If you are not an experienced listener, you might say they play louder. Not true. The real peaks of the music are compressed. The average might be higher but for the musical truth, you must have no peaks compressed whatsoever."

When you talk about dynamic contrasts and the ability to actually illuminate the subtle shades of volume in a recording, any mechanical reproduction system has limitations. The speaker has physical mass and inertia which have to be controlled and overcome in incredibly minute increments. The subtle micro shadings found in real music are often obscured by this mechanical nature of reproduction. Any device that can help mitigate these problems moves us closer to the live event. The 350M is such a device. I don't know why, whether it's their control of the speaker or their ability to deliver an increase of low-level detail to the speakers. Whatever the reason, heretofore hidden details and 'micro shadings' are far clearer with the Tenors than with any other amplifier. A small intimate recording such as Bach's Suites for Unaccompanied Cello [Janos Starker, Mercury SR3-9016] is civilized and
refined with subtle textures as delicate as real life. It's a perfect example of internal beauty mixed with an energy that scales directly with the music. Play your special go-to recordings and I guarantee that you will hear new-found detail and nuance.

If you assumed that the Tenors' ability to render micro details would make them ruthlessly revealing of everything in the audio chain, you'd be right. Every minor change and improvement is spectacularly easy to hear. Tube rolling in the preamp, switching cables in the phono, even moving Walker's Resonance Control Disks around, produced an immediate and undeniable change. These amps are a reviewer's dream.