EAR / Yoshino 834T Integrated Amplifier
Casting solid-state in the mold of tube amplification.
Review By Dick Olsher
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What is this EAR/Yoshino solid-state integrated amplifier doing in Toobman’ s listening room you ask? And why is he so enamored with its sound? Those are serious questions that will be answered in due time. Suffice it to say, the presence of output transformers is a pretty good indication that this is no conventional design. First, the mundane details. The 834T is said to draw upon the design bases of both the all-tube model 834 and the M100 transistor monoblocks. It offers 100 wpc of transformer-coupled MOSFET power together with six line-level inputs and one tape output. Both 4 and 8-Ohm output impedance taps are provided on the rear.
The front panel is adorned by two controls: an input selector and a volume potentiometer. Input sensitivity is sufficiently high to allow direct input from a CD player or DAC. In fact, I was quite successful in running my current reference, the Altmann Micro Machines Attraction DAC, directly in using Kimber Select KS-1030 interconnect. Originally intended as a tube/MOS FET hybrid, with a triode input stage, the 834T was put into production as all solid state. In the final analysis, the decision was made to configure the input stage using a pair of FETs on a plug-in board that is said to have the same characteristics as a twin triode tube but with the obvious savings of warm-up time and ease in matching. For the record, the designer still considers the 834T to be, by definition, a (solid-state) hybrid.
Always expect the unconventional from designer Tim de Paravicini. The iconic de Paravicini who bears an uncanny resemblance to Abraham Lincoln, and packs over 30 years of design experience into a lanky frame, has held since the 70s that tubes and solid state can be sonically equal. Here he has developed a solid-state amplifier that looks and feels like a tube design. The circuit topology is tube-like in that the 834T uses a high voltage B+ of 170 VDC as a single supply together with a wide-bandwidth output transformer that works in the same way as in a tube amplifier. The circuit is balanced from input to output and the output stage is push-pull (with several MOSFETs operating in parallel in each half of the circuit) in tube fashion. That is to say, according to Tim, 'NO COMPLEMENTARY nonsense' — both halves use similar devices (N-channel MOSFETs) as is the case in a tube circuit. Tim believes that the since it was grafted, if you will, with the 'genetic code' of a tube amplifier, the 834T has to sound the same as, for example, the EAR 861 that features a similar topology.
According to Tim, the reason for the high voltage is that the energy (number of Joules) stored in the power supply capacitors is proportional to the voltage squared. Hence, the higher the B+ voltage, the greater the power supply reserve. In addition to providing some impedance matching, the output transformer also ensures that there is no DC output present at the output should a MOSFET ever fail, thus avoiding expensive loudspeaker damage and enhancing long-term reliability.
The Sound
Solid-state power amplifiers never sounded like this before! Most of you reading this I imagine were not around in the 60s to witness first hand the introduction of a fledgling transistor technology. Touted initially as the death knell of tubes, it became slowly and painfully clear, that at least for audiophile applications, transistor-based designs had a long ways to go before deserving a place at a music lover’s table. But not before the debacle of entrenched tube gear makers such as McIntosh abandoning tubes in favor of solid state. The situation improved somewhat in the 70s with the advent of significant designs from Jim Bongiorno (e.g., the GAS Ampzilla). And finally, in the 80s and 90s the audiophile scene became crowded with a new solid-state persona. Gone was the grainy harshness of their early predecessors. Speed, detail, and smoothness were the order of the day. Numerous Mark Levinson and Krell designs competed for audiophile attention based on stupendous bass response and current drive. And having conquered most conventional distortion mechanisms, smoothness and detail were plentiful. Unfortunately, there was something fundamental missing in the solid-state sonic mix, which has kept me glued to tubes for the past 30 years. And that factor, dear reader, is emotional impact.
To a great extent, solid-state amplifiers resemble Imperial Storm troopers: clones lacking the soul and spatial conviction of the original musical experience. The terms pace and rhythmic conviction have in recent years become industry clichés, but speak to the heart of the matter. And while tubes seemed to unfold musical phrases with the full kinetic energy of the original event, 90s solid state consistently withered on the vine, dishing out a sterile imitation of the real thing. Enter the 834T. Its command of rhythmic nuances and microdynamics propelled musical lines along with foot tapping gusto. At the highest levels of music reproduction, the magic is definitely in the details. Musicians imbue the music with feelings though the subtle modulations of rhythm, volume, and pitch. Without such encoded detail music becomes mechanical in nature; there is nothing to differentiate it from that produced by a machine. And while de Paravicini’s tube designs have scored high in terms of retrieving the music’s drama and passion, I was not prepared for similar performance excellence from an all transistor design.
Let me assure you that despite the presence of output transformers, there was plenty of bandwidth in evidence. I think that de Paravicini takes pride in crafting wide bandwidth output transformers featuring frequency extension to 80kHz within 1dB or so. One of the side effects of reduced bandwidth is an overly liquid and soft sound, and that is usually a problem with single-ended triode designs where it is so hard to extend transformer bandwidth much beyond 20 kHz due to core saturation issues. This amplifier never lacked for transient speed. The attack portion was time and again laser quick and its associated decay was firmly controlled without spurious resonances or brightness.
Detail resolution was also a strong suit. And this was accomplished without exaggerating the upper octaves. It is so easy, especially under show room conditions, to become enamored of bright or etched sounding products, which under relaxed home listening conditions quickly induce listening fatigue. The 834T was rather refined and civilized sounding though the upper octaves, and is guaranteed not to exacerbate the sound of bright sounding speakers. Its tonal balance was fairly neutral in character. Its one minor deviation was a slightly warm sounding lower midrange, ala tube sound, which is far from being an issue in my book.
