EAR / Yoshino 834T Integrated Amplifier
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.
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.
Instrumental timbres were in general quite accurate, and in particular, midrange textures were gloriously sweet in character and capable of lovely harmonic bloom. Never confused or congested, the mids were voiced with world-class clarity. The transition from the core of the midrange to the lower treble was rather seamless. Soprano voice was given free reign to soar without any impediment and violin overtones were captured with their full harmonic sheen intact. The only other solid-state amplifiers in my experience to match this level of performance have been 47 Laboratory products — albeit at much lower power levels.
The traditional knock against MOSFET amplifiers has been a propensity toward soggy bass. Not so with the 834T. It laid a rock solid orchestral foundation. The power range of the orchestra never lacked in bass punch. Bass lines also exhibited excellent pitch definition. If you are cool about jazz, you will definitely be grooving over the authority and control with which double bass is dished out. Make no mistake about it: this amplifier is not just about lovely mids and pure treble — it can rock the house!
Difficult speaker loads were not an issue for the 834T. It did fine with the MartinLogan Vista using the 4-Ohm taps. And it spent many happy hours driving my newly acquired Magnepan MG-3.6/R loudspeakers (again using the 4-Ohm taps). The Maggies are notoriously finicky about associated power amplifiers. There is probably only a handful of amplifiers on the planet that mate optimally with them. To my great delight, the 834T coaxed the best sound I’ve ever heard out of a pair of Maggies. The degree of synergy was absolutely amazing: tight bass, sweet nuanced mids, refined treble, and above all else an unrestrained kinetic delivery that immediately put me in touch with the music’s emotions. The soundstage projected was wide and stable with a convincing depth perspective. And while image palpability did not quite equal the best of tube amplification, it came reasonably close.
There has been much talk about the need for high-powered amplification and current drive in the context of the larger Maggies, but as long as I kept volume levels such that dynamic peaks were not outrageously loud (say around 95dB SPL), I was able to red line the 834T without signs of strain or distortion.
Inputs: 6 line level plus tape output
Power Output: 100 watt per channel, 2 channels
Dimensions: 16 x 16 x 7 (HxWxD in inches)
Weight: 60 lbs.