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The Line1/Power1 pretty much guarantees absence of hum due to ground loops. Through the menu, pin 1 on balanced connectors can be grounded or lifted. The menu also allows audio ground to be changed from normal resistor grounding to grounding with no resistor to lifted completely with separate settings available for each channel. There are more grounding permutations than I can calculate but the bottom line is that the Tenor has unparalleled flexibility with regard to hum reduction. The VFD screen has a multitude of options for your viewing preference. You can select the Tenor logo, current settings or nothing, each with selectable timing and brightness levels. The Line1 can be programmed to set the volume to any level upon start up. A little too tired from a long listening session to have forgotten to turn things off? With the auto-off function you can preprogram the Line1/Power1 to turn itself off after a specific amount of time (including any amps connected to the built-in triggers).
Finding nothing acceptable off the shelf, Tenor designed their own remote control from scratch, allowing them to integrate the luxurious look and feel of the preamp. An internal USB port allows Tenor unlimited future updates to the microprocessor controlled section of the preamp for new functionality. For example the newest software update permits adjustment of the tape loop level, allowing the Tenor to be integrated into a home theater environment with custom level matching.

Circuit design. It’s all about HSI.
All Tenor designs revolve fundamentally around distortion but not in the way you might think. Tenor claims to tackle the issue of distortion in a manner significantly different than other high-end contenders. After years of R&D they developed a proprietary technology called Harmonic Structural Integrity (HSI) designed not only to reproduce static test frequencies but more importantly live dynamic music. HSI is the foundation for all Tenor designs.

If you are going to design the ultimate amplifier with minimal distortion, you can’t escape the oft heated debate about negative feedback. Sound trounces specs but the uses and limits of negative feedback show up in almost every high-end product blurb. As a primer, negative feedback is the process of sending a small anti-phase signal from the output back to the input to cancel distortion. This increases linearity but reduces gain. Yet it is not quite that simple. According to Michel, "every amplifier has a propagation delay which is that fixed amount of time the signal takes to go from input to output. When you take a sample of the output and inject it back at the input in reversed phase, that feedback signal will always lag behind the input signal.

"When a transient appears at the input, during the time it takes to travel to the output, the amplifier will overload for a very short period. This creates a lot of high-order harmonics which the brain is incapable of filtering. You end up with a well measuring circuit and a side effect of ringing and fatigue. Despite the improved static measurements, the musical event suffers." The only way to minimize the effects of negative feedback is ultra-wide bandwidth for a very short propagation delay. The problem according to Michel is that to achieve inaudibility, the bandwidth should extend into the megahertz region. That’s certainly not practical. He explained that Tenor’s research into dynamic performance discovered six fundamental problems associated with negative feedback:
  • Transient distortion
  • Feedback is not aperiodic due to the circuit’s propagation delay
  • Damping factor is nonlinear as a function of frequency
  • Creation of high-order harmonics unrelated to the input signal
  • Harmonic content of distortion changes dynamically with frequency and amplitude
  • The feedback loop goes unstable in the presence of a changing reactive nonlinear speaker load

To understand Tenor’s design philosophy, we have to take a brief detour into psychoacoustics and the nature of hearing. Bear with me, it will all tie together. Much of this theory dates back to the 1800s with the research of German professor Hermann von Helmholtz and his work on the perception of sound. Many of his theories have been proven with measurements and remain valued today. Additionally Michel’s current theories reference Fletcher/Munson and Olson. Michel’s designs are the result of his cumulative study and extensions of these psychoacoustic pioneers.

To understand Tenor’s HSI theory, let’s take the example of a pure 2kHz tone. In the frequency domain it is represented as one single line. Assume that it enters a theoretically perfect amplifier with absolutely no distortion, then gets output to a theoretically perfect speaker again with absolutely no distortion (impossible). The signal travels directly into the ear and there 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 actually acoustically hostile. The hearing process itself is non-linear and highly distorted. In fact most sounds in nature which are conducted or reflected are non-linear.