Triode Corporation TRX-M300 Monoblock Amplifier

Western Electric had a banner year in 1936. The introduction of the 300A, the mother of all triode power tubes, and the 91A cinema amplifier, a single-ended design based on the 300A, meant commercial success in the 1930s and 40s. The essentially identical 300B was introduced in 1938. It would have been impossible to predict then that these products would play pivotal roles in the directly heated single-ended-triode (SET) renaissance that began in the 1970s, mainly in Japan, and slowly moved westward. All things Western Electric (WE) became valuable in Japan. Old movie theaters were scoured for 91A and 91B amps that would then depart the USA. I would guess that just about all the extant original WE amps now reside in Japan.

It’s not surprising therefore that when Yamazaki-san, Triode Corporation’s designer, decided to design a reference-caliber 300B amplifier, he looked toward the WE 91A for general guidance—a decision that deserves a standing ovation. Think of Triode Corporation’s new M300 as a modern version of the WE 91A. This explains a tube complement identical to that of the original: a 274B rectifier, a pair of 310A receiving pentodes, and of course a 300B. However, paying homage to a vintage 1930s design should only go so far. For example, the gain of the 91A amplifier was colossal at 92dB due to the use of an input transformer and the cascading of two pentode gain stages. But that’s way too much gain for an audio amplifier nowadays partnering a typical preamp, which is capable of delivering at least a 2V signal. The M300 addresses this by dispensing with an input transformer and by using local feedback from anode to grid of the first pentode stage to decrease its gain and increase its effective headroom. In addition, the second 310A is connected as a triode in order to further reduce the overall gain. As a result, the input sensitivity is a reasonable 0.8V. The power supply has also increased in sophistication, following a high-end trend started by Audio Research in the 1970s. The 300B’s 5V filament supply is DC, because that’s the most effective means of lowering residual hum to acceptable levels when driving a high-sensitivity speaker. And for the record, the M300 is about as quiet as possible for an SET amplifier. Residual hum was simply not an issue even when driving a 96dB-sensitive loudspeaker. Likewise, the 310A filament voltage is rectified and actively regulated at 10V.

No global negative feedback (NFB) is used. The option of adding a 3dB global NFB switch was considered during the final design stage but was ultimately rejected on the basis of sound quality. There is usually no major incentive for using global NFB in the context of an SET amplifier as the output-stage source impedance is already fairly low and decent bandwidth and distortion figures can be achieved using a good-quality output transformer. The measured source impedance off the 6-and 8-ohm taps was 2.7 to 2.8 ohms, within the range of 2 to 3 ohms typical for such designs. The situation is of course considerably different for push-pull pentode and ultra-linear tube amps where large amounts of NFB, usually on the order of 20dB or more, are required to obtain a low output impedance and decent damping factor.

Both RCA unbalanced and XLR balanced inputs are provided. However, keep in mind that this is, after all, a single-ended amplifier. Hence, the XLR input should be considered strictly as a convenience in interfacing with a preamp or linestage lacking a single-ended output. The XLR input is routed through an op-amp buffer stage in order to reduce it to a single-ended input, so it’s best to avoid it if possible. Build-quality and finish are exceptional and speak to the care and reverence bestowed on what is intended to be a reference amplifier.

The M300 is shipped with a Psvane (aka Pavane) WE300B. The Psvane brand name is owned by a consortium of audiophiles within and outside of China and has gained a fine reputation for sound quality. This 300B is said to be a faithful replica of the original WE 300B in all respects, including materials and structure. That was good news since I’m the proud owner of two pairs of the Westrex Corporation 300Bs manufactured in the U.S. in 1997. (They are now temporarily unavailable, but Westrex is said to be resuming production sometime during 2014.) I was looking forward to a sonic shootout between these two purported exact replicas of the original. To that gladiatorial mix I added a TJ-Full Music mesh plate from the TJ factory in Tianjin province, China. This is a 300B variant that I’ve enjoyed very much over the years due to its vivid tonal colors and dynamic sound.

Detail with Ease

The M300 delivered what can only be described as magical image solidity. Solid-state amps would kill for it, and even tube push-pull designs can’t quite compete. Image outlines were sculpted with palpable presence and anchored firmly within a spacious soundstage. In my experience, the sensation of reaching out and touching someone engendered by this amp has only been matched by a handful of SET-design tube amps. This spatial attribute should not be understood to merely denote static precision but to also encompass the ebb and flow of the harmonic envelope of each instrument. The end result was a convincing, breathing, 3-D spatial expanse. An illusion to be sure, but with my eyes closed, the impression felt about as real as it gets from a two-channel audio system.

Bandwidth and transient speed were pretty impressive for an SET amplifier, and this speaks to the quality of the output transformer. The single-ended output tranny has traditionally been a weak spot in many designs, accounting for a bandwidth barely exceeding 20kHz and consequently textures that are overly liquid with the consistency of maple syrup. By contrast, the M300 sang sweetly but with transient clarity and sufficient transparency to penetrate deeply into a complex mix. There was a fabulous amount of detail to behold, and I’m talking about detail that floated naturally to the surface rather than detail that was artificially highlighted by an excess of textural brightness and glare. What was so consistently wonderful about this amp was its relaxed manner, its fluidity of motion, and its ease of expression. It never appeared to work hard or complain even when driven to loud volume levels. It sounded far more powerful than its 8 watts power rating would suggest, but keep in mind that it was mated with a 96dB-sensitive load throughout the evaluation period. In fact, I would hesitate to recommend a less-sensitive load. There may be exceptions, however, especially if you plan to listen in a small room at low volume levels. In any case, I would not breach a sensitivity threshold of 92dB. I experimented with both the 6-and 8-ohm taps and preferred the 8-ohm set for its better bass damping and definition. When multiple taps are available, it’s always wise to try at least a couple of the available options to determine which sounds best in your system. Bass lines flowed with plenty of boogie factor and possessed a tuneful character that blended nicely with the core of the midrange. I didn’t expect nor did I obtain the bone-crushing low end typical of high-current solid-state amplification, but I was constantly surprised by the M300’s dynamic prowess. The ability to accelerate an orchestral crescendo from soft to loud was simply breathtaking, and in this respect it exceeded the macrodynamic performance of high-power push-pull amplifiers. The M300 offered a fitting testament to the potency of the first watt. It’s the first watt that sets the stage and ignites the microdynamic palette. And if the first watt doesn’t get the job done, there’s not much need in my book for another 99 watts like it.

Subtle Differences

As for tonal balance and timbre fidelity, there were noticeable differences among the three competing 300Bs. It was all the more surprising in the case of the Westrex and Psvane 300B since both are said to be exact replicas of the original WE design. The inescapable conclusion is that there must be some subtle construction and/or material differences between these two copies of the original. The Westrex possessed the best spatial resolution and on properly miked recordings delivered startling focus. It was able, for example, to resolve a naturally recorded drum kit without spatial smearing. It was also the sweetest and most refined-sounding of the bunch.

If music were a beauty contest, the Westrex 300B would surely be the winner. However, there’s more to music than beauty and the Psvane delivered a slightly more forward and energetic presentation, highlighting the fact that the Westrex is simply a bit too laid-back. When it came to timbre, the Psvane was nothing short of amazing, superbly rendering soprano voice with vivid colors. As you can surmise, the Westrex was far more forgiving of less-than-ideal recordings. The TJ 300B was no sonic slouch, but it was outgunned when it came to textural purity and timbral fidelity. Its major sonic calling card was a punchy big-bodied midrange that could generate plenty of visceral excitement. To confess, I could live happily ever after with the Psvane WE300B, though your ultimate 300B choice will no doubt be affected by the associated front end and matching loudspeakers.

At its best, partnered by a first-rate front end, the M300 is capable of spooky dimensionality and image outlines that are palpable to the max. If at the end of a long day, you simply wish to kick back and enjoy the music with your favorite beverage in hand, I can’t think of a finer amplifier with which to unwind and forget your troubles. It is a superlative achievement from the prolific mind of Yamazaki-san and one that will do wonders for your mental health without devastating your bank account. The 300B has often been thought of as a civilized and refined member of the directly heated triode family. But as the TRX-M300 clearly demonstrates, there is much more to its story than that. The Triode TRX-M300 showcases the beauty and dynamic power that is the full potential of the much-venerated 300B, and therefore earns my highest recommendation.

SPECS & PRICING

Power output: 8 watts into 8 ohms
Output impedance taps: 4/6/8/16 ohms
Frequency response: 10Hz–50 kHz (0, -3dB)
Total harmonic distortion: < 0.1% (1kHz)
Signal to noise ratio: 87dB
Input sensitivity: 800mV
Input impedance: 100k Ohms
Weight: 60 lbs.
Dimensions: 430 x 340 x 185mm
Price: $14,000/pr.

Triode Corporation of Japan
U.S. Distributor (Twin Audio Video)
PO Box 681
Loma Linda, CA 92354
(909) 954-2175
triode.co.jp

Associated Equipment

Basszilla Feastrex and Platinum mk2 DIY speakers; Yoshino-EAR DAC, April Music Eximus DP1 DAC, Sony XA-5400 SACD player with ModWright Truth modification; Kuzma Reference turntable; Kuzma Stogi Reference 313 VTA tonearm; Clearaudio Da Vinci V2 MC phono cartridge; Pass Labs XP-25 phono stage; Pass Labs XP-30 line preamplifier; FMS Nexus-2, Wire World, and Kimber KCAG interconnects; Acoustic Zen Hologram speaker cable; Sound Application power line conditioners