June 2004

Eastern Electric MiniMax Power Amplifier
Another High Value Product From China
Review By Dick Olsher
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  Eastern (as in China) Electric, is a partnership comprising Bill O'Connell of Morningstar Audio Imports and Hong Kong designer Alex Yeung. Although not explicitly stated, the MiniMax line presumably refers to Minimal price and Maximum performance. Yeung's design philosophy is influenced by his love affair with vintage tube gear and belief in the superiority of tubes for music reproduction. He is determined to offer the audiophile superior tube sound at affordable prices. Eastern Electric's debut of its MiniMax pre-amplifier made quite a splash last year (see Karl Lozier' s world premiere review) and has garnered this startup much credibility.
Do not confuse low prices with low quality. Yeung insists on using top-quality parts, especially transformers. He also uses tube rectification whenever possible. Alex takes an hour ferry ride from Hong Kong to the mainland China factory to discuss design and production issues with the engineering team. The emphasis is on quality and all units are burned-in for 48 hours to ensure reliability. In time-honored high-end fashion, he lets his ears be the final arbiter of sound quality. The art of voicing a product is a difficult task for an engineering persona. Ideally, it requires a passion for and an appreciation of live music, which is the sort of mindset Alex brings to the job at hand.

The MiniMax amplifier is a low-power, push-pull, design. Its 8 watts per channel are suitable for driving a high-sensitivity loudspeaker. If your loudspeaker is rated at less than about 90dB/W/1m, then your best bet is to look elsewhere for compatible amplification. The chassis is compact and is very nicely finished. A pair of 6BM8 miniature tubes makes up the tube complement of each audio channel. The good news is that the 6BM8 is still in production at the Svetlana factory in Russia and perhaps in China so it is in plentiful supply. A single 6BM8 contains in a single glass envelope a power pentode and a high-gain triode. A pair of such tubes, where the pentodes are connected in ultralinear fashion, makes for a very economical push-pull amplifier design. And that's basically the circuit topology of the MiniMax.

One triode section is used as an input voltage gain stage, while the other triode is used as a cathodyne phase splitter. This is a time-honored phase splitter, featured in many 50s power amplifiers, including the Dyna Mark III, with the twin virtues of simplicity and excellent balance. Global feeback is applied between the output transformer's secondary winding and the input stage, usually a necessity with a cathodyne phase splitter. While many manufacturers opt for an inexpensive solid-state diode bridge rectifier and smoothing filter (even in much more expensive tube gear), the MiniMax features a 5AR4 tube rectifier and a genuine pi filter.

The Sound
Pour yourself a warm bath and settle back with a glass of wine. You have just entered the MiniMax zone, a domain of luxuriant harmonic textures that envelopes and caresses the aural pleasure centers. Much like the mouth taste of rich, dark chocolate, this amplifier imprints itself over musical textures. Never thin or harsh sounding, it weaves a liquid sonic tapestry that does wonders for stress relief.

It has been suggested that the preponderance of even-order harmonic distortion is responsible for tube-like sound. There may be a kernel of truth in that, but I find such a simplistic, wide-ranging idea rather suspect, especially in the context of a push-pull amplifier. A push-pull output stage excels in cancellation of even-order distortion products, so one would expect the residual distortion to be predominantly odd-order. That appears to be the case with many EL34 based designs, whose bluesy tone may be derived from odd-order harmonic distortion residuals. However, a ultralinear connection of the output stage, where the screen grids are fed DC bias voltage from taps in each half of the output transformer's primary winding, is known to produce a sound that approximates that of a triode. The seminal article that popularized this topology was published by David Hafler and Herbert Keroes in the November 1951 issue of Audio Engineering and still makes for interesting reading. The circuitry described in this article, of course, became the basis for the legendary Dynakit Mark III power amplifier. The ultralinear connection definitely works wonders for the MiniMax, whose sound transcends its pentode origins and morphs into a sweet and lush tone, that is very much triode like.

So far so good, but unfortunately out of the box the MiniMax lacked the immediacy and dramatic tension so adeptly reproduced by a well-designed single-ended, directly-heated triode amplifier. Its presentation was so flaccid as to suggest a dose of Viagra. The music's microdynamics seemed stuck in first gear. In addition, image outlines lacked convincing focus and soundstage extension was constrained in terms of depth and width. No wonder, the thing literally put me to sleep. Since Bill O'Connell, the importer, was thoughtful enough to include a quad set of used vintage Amperex 6BM8 (ECL82) together with a Mullard GZ34 rectifier tube, this seemed like a good time to try these tube substitutions.

The Amperex tightened up image outlines and gave a better accounting of transient decay. But the real shocker was the Mullard rectifier tube. The Mullard is generally recognized as the best of the best, but has been out of production for over 30 years. However, Ebay is usually a good place to seek out this tube as well as many other vintage brands. If you think that a rectifier tube is not a critical tube in terms of sonics, and that any new production 5AR4/GZ34 brand will do, you would be sorely mistaken. The Mullard lit a fire under the soundstage. It infused the music with a believable dramatic flair. The emotions are in the details, the performer's inflections in volume, pitch and time that encode music with feelings. Female voice was now allowed to sing with newfound meaning, to caress the lyrics with a satisfying combination of sweetness and dynamic authority.

What about the frequency extremes, you ask? Well, the MiniMax gave a reasonable accounting of itself. The upper bass was well integrated with the core of the midrange. The transition from the mids to the treble was clean without the brightness and glare that afflict so many modern tube amplifiers. However, do not expect kick-ass bass from this puppy, as current drive is pretty limited. Do take advantage of the impedance 4, 8, and 16 ohm impedance taps. They are provided to allow optimum coupling of power from the amplifier to the load. Be sure to experiment with all three selections to determine the overall best combination of bass damping and dynamic range. Driving my BassZilla Platinum Edition loudspeaker, the 8-ohm taps sounded best.

Conclusion
Assuming you already own a compatible loudspeaker load and are willing to go the extra mile and outfit the MiniMax with a vintage tube complement, including a Mullard GZ34/5AR4 rectifier, you will be guaranteed a special sonic treat. It is a luxuriant and liquid sounding amplifier in the best tradition of vintage tube gear. The MiniMax should prove to be a godsend for a bright sounding loudspeaker. Featuring a musical midrange and without a glaring sonic deficiency, the MiniMax amplifier represents a very good value for the dollar.

Specifications
Type: Stereo amplifier
Output Power: 8 wpc (8 ohms)
Frequency Response: 15Hz to 30kHz 
THD : 1.5%
S/N Ratio: 83 dB
Input Impedance: 120 kOhm
Output Impedance taps: 4, 8, and 16 Ohm
Channel Balance: <0.5 dB
Dimensions: 316 x 205 x 150 (W x L x H mm)
Weight: 9 kg (19.8 pounds)
Price: $1,350

Company Information
Eastern Electric
Importer: Morningstar Audio Imports
44 East University drive
Arlington Heights, IL 60004

Voice: (847) 255-1150
Fax: (847) 255-1878
E-mail: bill@morningstar-audio-imports.com
Website: www.eeaudio.com