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MiniMax Tube Power Amp

Tiny tubes can deliver

[MiniMax with tube cage removed]

Product: MiniMax Tube Power Amp
Manufacturer: Eastern Electric Audio - China
Distributor: Minimax Audio - Europe
Approx price: 1190 EUR, in Germany (YMMV)
Weight: 9kg
Dimensions: 316mm (W) x 205mm (D) x 150mm (H)
Tube complement: ECL82/6BM8 (four), 5AR4/GZ34 (one)
Reviewer: Hartmut Quaschik - TNT Germany
Reviewed: July, 2004

My First Encounter with Chinese Hi-End Audio

When I had been in China five years ago, visiting a friend who was involved in distributing mobile phone assembly and checking apparatuses, I asked him: "Well, what kind of hifi do they have here?", and we visited some places.
I was surprised to find indeed a lot of companies involved in producing hifi of all kinds, be it tube power amps, single tubes, or beautifully manufactured loudspeakers stylish as Sonus Faber. Prices were quite low, too.

Now, more and more Chinese companies produce OEM, e.g. for Red Rose Music, the latest company under guidance of Mark Levinson, or sell directly under their own names, e.g. Shanling, or in this special case, Eastern Electric.

The MiniMax power amp reached me double boxed and safe. I unpacked it and the craftmanship, which resembled more Japanese tube amps like Uchida/Sun Audio, gave me a positive feeling. There is also a German instruction manual giving all the necessary information to fire up this tiny power amp.

External details

On the front, there is a long power switch and a bright blue light emitting diode (LED). Is that LED annoyingly bright ! My first question to the European importer, Mr Posingis, was: "When will this LED be changed to a neon indicator lamp ?", he said: "This is one of the first things I want to change in production."

On the back, there are two RCA phono sockets for connecting your line cables, an IEC power cord inlet with integrated tube holder, and outputs for three different loudspeaker impedances: 4 Ohms, 8 Ohms, 16 Ohms.

Viewing the top, there are five tubes protected by a tube cage, four of them of type ECL82/6BM8, and one of type 5AR4/GZ34. The last tube is for high voltage rectification. Instead of silicon rectifiers, a tube rectifier is used here. The ECL82 is an old European double tube consisting of a triode and a power pentode in one glass bulb. Small Push-Pull power amps with this power triode have been used in Europe in the 60ies commonly.
There are also four pieces of iron, with beautiful end caps, on the top. These are two power transformers and two output transformers.

Internals

Opening the base board is quite easy. One can detect the power supply choke and a well executed point-to-point wiring. Somewhere else I read that the circuit consists of one triode half in the input, another triode half as phase splitter having the two opposite phases at cathode and anode, and the two pentode halves as push-pull output tubes.

[MiniMax power amp internal view]

Power On

When I first fired up the Minimax in my big system in my listening room, a considerable hum came out of my speakers.
I searched for the cause, which then was the connection between signal ground and safety ground. They should be disconnected in power amps generally, like they are in Naim power amps, for example. Signal ground and safety ground should be connected at the preamp only, otherwise there is a ground loop, which always causes hum.

So first listening was with the ground connectors isolated at the mains plug, then I tried an isolation transformer, and finally - with permission of Mr Posingis, of course - I opened the power amp and disconnected the signal ground from the line connector ground. The case must kept connected to safety ground, for safety reasons, of course. Don't open the power amp yourself and change something, if you are not familiar with electronics, because high voltages may be lethal.

When I reported this back to Mr Posingis, he handed that information over to Eastern Electric. Future production samples will have the signal ground separated from the safety ground.

Sound with high efficiency loudspeakers

Once the hum problem was solved, proper listening could take place. In my main listening system in my dedicated listening room I have high efficiency loudspeakers playing. They consist of two way horn loudspeakers, in the bass there is a 12 inch Altec 414B woofer playing in a 150 liters cabinet with open back side, in the mid and treble from 1000 Hertz there is an Altec 802 with JBL 2370 constant directivity (90 degrees horizontal by 50 degrees vertical) horn playing. Both ways are separated by a 6dB crossover with a lot of correction elements and an equalisation of the horn range. This loudspeakers has about 97dB/Watt efficiency and is an easy 8 Ohms load for any power amp. I used the 4 Ohm taps of the output transformers to get the tightest bass possible.

For long years I am building transistor and tube amps of my own, and I have still a small single ended 2 * 4 Watts tube amp which I had built 6 years ago, and was good enough to sell my Uchida/Sun Audio 2A3 and 300B power amps and not to buy a Shindo Palmer. Regarding push-pull power amplifiers, I owned the Conrad-Johnson MV45 and had listening experiences with Quad II, Leak TL20, Radford, Raphael power amps and Vacuum State (Allen Wright).

Though I am not a tube guy. What I like about tubes, is their natural presentation, their life-likeness. What I do not like about tubes, is when they are overly soft or colored or boring. Most tube power amps sound rose-tinted to me, some are soft in the bass region, some are soft in the treble region.

On the other hand, most transistor power amps are sounding really bad. Even well reputated stuff like Mark Levinson's ML29 or Cello Encore 50, which I had both playing in my listening room, failed to communicate music to me.

I am listening to pop music mostly (say 60%) and if a power amp cannot rock, well then it is nothing for me. So then, I am listening most times with my DIY transistor power amp 2 * 30 Watts.

To my surprise, the 2 * 8 Watts Minimax sounded nearly indistinguishable to my transistor power amp. It has real power, has a solid, yet natural and deep bass, has high resolution, can be fast, shows neither soft nor grainy colorations, times like Naim ... Yes ! It also reminded me to Allen Wright's Push-Pull tube power amps, which sound excellent, too.
I had the Minimax playing for some weeks without interruption (the power consumption and heat dissipation seems quite low for a tube amp) and several times could not tell whether my own reference power amp or the Minimax was playing. I even did some listening sessions for reviewing the Origin Live Encounter tonearm with the Minimax.

When I compared my reference power amp and the MiniMax directly, differences are there, but very small. My own power amp is a bit more transparent in the midrange and has just a bit more resolution in the treble. The differences had been bigger in the beginning, and got smaller as the MiniMax ran in.

The Minimax is suitable for all types of music, be it classical (I played Holst's Plants and Sibelius big orchestral works), be it Jazz or modern electronic Pop like Massive Attack or St.Germain, or heavily processed sophisticated Pop like Tori Amos's Choirgirl Hotel.
The MiniMax never choked or struggled, always sounded free flowing and at the same time firm and honestly. In other words, the MiniMax has no preference for certain types of music, like some other tube power amps have. You surely remember hifi show demonstrations with clean Jazz (one female voice and one guitar recorded in a church) or Baroque classical music. This demonstration music is easy for those power amplifiers with no control in the bass region, but once you play a loud passage of rock music through them, they fail.

Sound with low efficiency loudspeakers

In my living room I have a smaller setup with vintage Naim electronics and small bookshelf loudspeakers. These speakers are clones of the famous Linn Kan, and of about 82dB efficiency, but straight 8 Ohms load.

One evening I took these speakers to my listening room and connected them to my reference system. I then did again comparisons between my reference power amp and the Minimax.

Surprisingly, differences are detectable, but remain small. There is just a hint of soft bass, when listening to big symphonic orchestra. That is all. Again, the MiniMax was able to drive the speaker to give the impression of a Wall of Sound, like my own power amp can.
The Minimax got loud enough for me with either pop music or classical, but I assume, that it won't be enough to party your entire house with 82dB loudspeakers. I wasn't able to drive the Minimax into distortions while keeping the listening level sane. So it might be that 8 tube watts are like 20 Naim watts (like in the first Naim Nait integrated amplifier).

In this configuration, I tried out what were the sonic differences between the impedance taps 4 Ohm, 8 Ohm, 16 Ohm of the output transformers. With 4 Ohms, the Minimax had grip like my transistor, with 16 Ohms, it sounded round like your neighbour's single ended tube, and with 8 Ohms, it was in between. So you have a real choice to select the sound you like.

Conclusions

The MiniMax is one of those rare tube power amps which are nearest to a piece of wire with gain.

I recommend the Minimax to all enthusiasts who want the benefits of tubes without their drawbacks. The Minimax is not only a Best Buy due to its price tag, but also excellent in absolute terms.

Copyright © 2004 Hartmut Quaschik - www.tnt-audio.com

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