Mike Malinowski
Financial Interests: click here
Source: Walker Black Diamond turntable; Walker Reference phono preamp; Tenor Phono 1, Clearaudio Goldfinger Statement Cartridge
Preamp: Tenor Line1/Power1VTL TL-7.5 Reference
Amp: Tenor 350M; darTZeel NHB-108 
Speakers: Wilson X-2 Alexandria Series II
Cables: Silent Source Music Reference;
Stands: Custom Renzetti Racks, VPI phono stand, Zoethecus, Walker Prologue Amp Stand
Powerline conditioning: Equi=Tech, Walker Audio Velocitor, PS Audio 300
Sundry accessories: Walker Audio Valid Points resonance control discs; ASC tube traps; Argent Room Lens; separate 100-amp sub panel feeding five dedicated cryo'd outlets; Loricraft Model 4 record cleaner; Klaudio ultrasonic, Walker Talisman
Room size: 29’x 19’ x 10 full ASC acoustic design. 
Review component retail: $50'000 Canadian

Whilst not quite the Rodney Dangerfield of audio, the excitement of a phono preamp tends to pale by contrast to the sonic and visual panache of the finest speakers, the exotic elegance of the finest amps and preamps or the leading-edge tech of today’s digital. Yet whilst us vinyl enthusiasts revel in the newest golden age of analogue, brilliant designers continue to dramatically push the boundaries still within the ultra high-end of phono. Each time when we appear to reach vinyl’s ultimate potential with the resolution of the inscribed grooves fully revealed, along comes a groundbreaking product like Tenor’s to demonstrate how there remains untapped information to be mined from this supposedly archaic medium.

One of the great advantages of reviewing is meeting designers and hearing their insights. Most are brilliant, quirky and generally fascinating. With Michel Vanden Broeck and Jim Fairhead, our many discussions were eclectic and wide ranging. With R&D spanning over five years, it’s logical to wonder why such a long development cycle for a product that has very few of the bells and whistles of a line stage, far less switching and presumably far lower complexity. And let’s not kid ourselves. $50'000 buys a nice car; no, make that a really nice car. Yet this is just a phono stage. However, like other things in life, this onion has many layers and the final conclusion is often not the initially obvious. A phono preamplifier delivers performance that must exceed that of the linestage or even power amp. The Tenor’s gain of 70dB (it actually approaches 80dB in the bass taking into account the RIAA equalization) blows away their line stage’s gain of 20dB. Even the mighty Tenor 350M HP monos only muster a gain of 32dB. An ultra-low noise environment, an amplification factor of 10’000, multiple gain stages and the use of tubes all produce significant design challenges. In some respects then the phono stage actually has one of the more difficult jobs in the audio chain. And as a source component, any intrinsic artifacts, noise or imperfections are amplified and passed on. There is no removing noise down the line if it exists at the source.

Visual. Tenor’s is a statement product. As such, form and function matter equally. The exterior design of an exotic car matters. The old-world elegance of a Patek Philippe watch matters. A well-heeled audiophile spending $50K on a phono preamp is making a statement. Tenor understand this and produce a consistent look throughout their line, with a circular information screen embedded in a highly polished front plate that exudes rich elegance. The subtle angles of the handpicked Cherry wood are CNC milled, offering an utterly unique luxurious look. Tenor components are visually unmistakable. 

History. I have significant history with Tenor both as retail consumer and reviewer to include interviews and factory visits. This exposure gives me and hopefully the reader some deeper insight into their design philosophies. In 2000 and as a retail customer, the OTL 75i was my first introduction to Tenor. It was tube magic. I immediately contacted them for an opportunity to review their new 300M hybrid monos. Unfortunately a confluence of bad management decisions and a faulty output transistor proved to be the undoing of the old Tenor Company. For a complete history, I refer you to my original 350M review which details the rise, fall and rebirth of Tenor Audio. Today’s Tenor is located in Montreal/Canada, well-funded, professionally managed and owned by a passionate and dedicated group of audiophiles. They have a Lexus mind set of "the relentless pursuit of perfection". No entry-level products, no accessories, just the finest components that current technology permits.

Circuit design. It’s all about HSI. Whilst the OTL design was impractical for high-powered versions, its core technology remains present today in all Tenor designs as their unique and proprietary distortion management technology called Harmonic Structural Integrity (HSI). Superficially, HSI could be dismissed as mere marketing fluff.  But if you spend time discussing their technology with Jim and Michel, you begin to understand their rather unique and comprehensive approach to distortion management not for static test frequencies but for real dynamic music signal. Certainly negative feedback addresses distortion. That is the process of sending a small out-of-phase signal from output to input. This lowers gain and reduces THD. If it were so simple, life would be easy. Alas, every amplifier suffers propagation delay as the finite amount of time it takes the signal to travel from input to output. Feedback always lags. According to Michel, when a transient burst appears at the input, during the time it takes to travel through the circuit, the amplifier will be overloaded for a very brief moment. This creates higher-order harmonics which the brain is incapable of filtering out. More on this later. Circuits with feedback might measure well but despite improved static measurements, music playback suffers. Michel feels that the only way to minimize the effect of propagation delay in a negative feedback circuit would be an ultra-wideband design extending well into the 10 megahertz region – an impractical solution. [This would be an avenue Soulution for example pursue - Ed.]

Although I went into significant detail on the theory of Tenor’s HSI system in the prior Tenor Line 1/Power 1 product reviews, the theory is relevant also for the Phono 1. To understand Michel’s design philosophy, we have to take a minor detour and touch on psychoacoustics, the nature of hearing and how the brain interprets sounds. Michel bases much of his theory on the research of Hermann von Helmholtz, a 19th-century German professor and his original work on the perception of sound. Many of his theories have proven out and are valued even today. Michel's work also references Fletcher, Munson and Olson. These pioneers along with Michel's original work form the basis of Tenor’s Harmonic Structural Integrity theories and designs. During my discussions with Tenor prior to the review of the Line 1 preamp, we spent hours discussing the psychoacoustic theory of sound and how it relates to amplifier design. Actually, I spent hours listening, Michel and Jim hours explaining until I finally got it. My explanations written for the preamplifier review represent my best understanding of their theory. As an introduction, I've included some of it below. 

To understand Tenor’s HSI, let’s take the example of a pure 2kHz tone (Figure 1). In the frequency domain, it is represented as a single line assuming that it enters a theoretically perfect amplifier with absolutely no distortion, then outputs to a theoretically perfect speaker again with absolutely no distortion - wishful thinking. The signal travels directly into the ear, then through a complex route that includes the ear canal, eardrum, vibrating bones, a liquid-filled sack, the cochlea, special nerve fiber sensors and ultimately the brain. The path is not a smooth acoustic environment but acoustically hostile. The hearing process itself is nonlinear and highly distorted. In fact, most sounds in nature which are conducted or reflected are nonlinear.

By the time our pure 2kHz sine wave passes through the circuitous passage of the ear (right), this sound wave is highly distorted with added harmonics, in some instances up to 14th order (Figure 2). But remarkably, over the millennia our brain has developed a filter mechanism which instantaneously subtracts self-generated harmonics. The result is the brain’s recognition of the absolute purity of the 2kHz tone, not the harmonic distortion induced by our ear canal. The human ear and brain have evolved biological ‘DSP’ which detects and recognizes the original signal and rejects all other naturally occurring noise and distortion. Even with complex natural sounds, the brain is able to process a large amount of information in the very same manner.

Normal hearing distortion can be 5% or more. So if every sound is first distorted then filtered by the ear/brain interface, why should comparably small amounts of amplifier distortion be any issue? Good question. The answer lies in natural.

The human hearing process can only filter distortions which are naturally formed in the ear and outer environment. That is why normal sounds in nature never fatigue us. One could listen to the sounds of the ocean, the mountains or the forest indefinitely. Has anyone every complained that the sound of crashing waves irritates? But start to add artificial sounds especially of electronic amplification and things change. Subtle electronically-induced distortions are not what the brain has learnt over the millennia to recognize and filter. Because it cannot, the results are hardness, lack of purity, fatigue and unnatural sound. Attempts to reduce electronic distortions via feedback and other means produce a complex signal of music and with it "unnatural distortion which the brain doesn't recognize as natural." This is profound.

Back to our example of the pure 2kHz tone. The pattern of ear-induced harmonic distortion is complex and nonlinear in both frequency and amplitude. Yet the structure of this distortion is well defined and experimentally proven. Now we come to Tenor’s design philosophy. Instead of trying to reduce amplifier distortion with feedback, what if one could develop a circuit that had intrinsically low distortion, then tailored the residual distortion curves to mimic those which occur naturally in the ear? In theory, the brain should discard this residual distortion and fixate only on the pure music signal. Stated another way, if the harmonic distortion curve, its slope and geometry matched the natural curve of our ear distortion, the brain would instantaneously and transparently filter out said distortion. We’d be left hearing accurate timbre and spectacularly clean music. This is Tenor’s single unifying design philosophy summarized as HSI.