XINDAK MT 1 TUBE INTEGRATED AMPLIFIER
Thanks to Calvin Tseng of Lotus Audio Imports in Oakland, CA for providing us with this amp for review - publisher
The Xindak MT-1 is a small class A integrated tube amplifier rated at a modest 12.5 watts per channel. The company is well known in China and for good reason. I already own a Xindak XA6950 solid state class A amplifier that is exceedingly good. Can a small 12.5 watt amplifier deliver the goods too? With my small 10x13 listening room, the idea of trying the Xindak tubed integrated raised a sense of anticipation not felt since before the holiday season as a child. Having been re-introduced to tube amplification over the past few years, I was guardedly optimistic.
The MT-1 is a handsome unit successfully combining a classic retro look with clean modern form. It is less wide and deep than traditional integrated amplifiers which will be a plus for many. The sheet metal is heavy gage, more befitting of 1965 than today. The front has a simple control panel in the center consisting of an input selector, ALPs volume control, and a power button. Build quality is solid with unquestionable fit and finish. There is a removable cover that reveals the warm glow of the tubes sitting up front and center. The proximity to small children dictated whether the cover was used or not during the review period. The look is modern retro with the tubes exposed while taking on more of an industrial look with the cover on. The amplifier comes with optional real wood or brushed aluminum trim that is front and center. My sample arrived with the brushed aluminum.
There are three tubes per side for a total of six tubes. Each completely separate channel uses one 6F2 pentode tube for the gain stage and two EL84 tubes in a push-pull configuration for amplification. The amplifying stage takes a leap and runs in class A. Simply put, class A is when the amplifying stage is biased to constantly run at full rate. The output is shunted and wasted as heat until a signal is present and even then only the amount of output required is actually sent to the speakers. A quick test showed the MT-1 uses a rather constant 90 watts when turned on, even with no music playing. To use an automobile analogy, this is similar to flooring a car’s engine with the clutch pushed in. The car will only move as the clutch is let out. Why would an amplifier run in class A mode as opposed to the more efficient class AB? There are sonic benefits by avoiding turning off the tubes. Running an amplifier in class A does not guarantee great sound. The execution of the design is critical. Everything counts.
The rear of the chassis is quite simple with connectors for a removable power cord, three RCA level inputs, and 4 or 8 ohm speaker taps.
Unpacking the Xindak MT-1 revealed a short but decent user manual, a bag which can be used to protect it from dust, and white gloves for protecting the tubes from fingers. It also revealed an unnerving sound. There was an extra screw sliding around in the chassis. I opened the amplifier up and could not detect exactly where it was meant to be. Not all was lost. Internally, the build quality was quite solid with an old school feel. Expectations regarding the sound started to rise. Concern over the extracted mystery screw still looming, I hooked up the amplifier for a quick sanity check. All was seemingly OK. Whether this is representative of the quality control or a fluke is something to ponder even with the rugged build quality. Those with a distaste for bright blue LED's need to be aware this the MT-1 has the annoying “Bright Blue LED Syndrome”. When I first turned it on, it glared at me, distraction from the glow of the tubes, and annoying enough to warrant black electrical tape over it.
The stock power cord was left in the box and a simple shielded Volex power cord that was already in place was used. Interconnects were the Blue Jeans Cable LC-1 and the speaker cables were the Kimber 4TC.
A Pacific Valve modified Lite DAC AM served as a DAC for an old Nakamichi MB2-S used as transport. Additionally, a Pioneer Elite DV97A was connected via its analog outputs straight into the Xindak amplifier in addition to the digital output which fed the aforementioned DAC. The speakers used for break-in were quite inefficient at 85db and proved to not exactly mesh with the Xindak. Finding speakers to match the amplifier was an arduous task. My favorite set of speakers, those that mesh the best with my listening room, are a smaller version of the GR Research OB-5 utilizing only three drivers. In my small listening room, they are more than enough and surprisingly good. The crossover was a joint effort between Danny Richie and myself. One caveat here is that the impedance curve looks more like an EKG of somebody getting some exciting news. Later in the review we'll show some graphs of my mini monitors exploring exactly why a tube amplifier may not like a bumpy impedance curve. Next speaker? In the end, there were two that meshed well with the Xindak. One set was the HSU HB1 MK2 speakers rated at 92db efficiency in half space and a set of DIY speakers rated at 87db efficiency. One common theme between the two is that they both have a flat impedance curve across the critical midrange. This turned out to be pretty key performance-wise.
HOW DOES IT SOUND?
After about 50 hours of play time, it was time to listen. When I walked into the room, my wife had already loaded some classic rock into the system. I immediately flashed back 31 years ago as an 8 year old performing air guitar to Elvis records played on my Mother's vintage system. The only connection I could make was that there's just something about tubes.
I sat down with a glass of Smuttynose to sip. Miles Davis, “Kind of Blue” on CD seemed the obvious choice after a rough day at work. I was immediately drawn into the music. What laid in front of me was just music. All the air of the horns was present with lots of detail, none of it being annoying. The sound stage was exceedingly wide and slightly less deep than I usually find this release. Even with 12.5 watts, I was able to reach decent listening levels in my small room even with 87db efficient speakers. I forgot all about being analytical and was just drawn away. I sat and listened to the entire CD, forgetting about my beer, and everything else around me. It turned my listening room into a tiny decompression chamber.
I played some of Miles Davis for my wife who responded; “Absolutely the best sound yet in our listening room”. This was immediately followed by a look of fear on her face that I would buy yet another amplifier. I have at least five in house if you don't count receivers. These were strong words from her considering that the Bryston B100 SST and Forte Model 5 are both quite nice in their own ways. The Xindak XA6950 sounds slightly better than either in my opinion. In comparison with the MT-1, the XA6950 is quieter, much more powerful, a little more transparent, and has more pristine highs. The MT-1, however, has a sense of liquidity often sought by the purists. There is just something about it that sounds even more real. It soon became an old friend and parting would be painful.
I later played Queen's Greatest Hits which somehow beckoned my children in to come listen. The five year old immediately turned the volume into distortion territory. After reigning that in, I noticed the panning back and forth in “Another One Bites the Dust” was wider than ever. The bass was decidedly strong yet a bit slower than the solid state counterparts in house. Exposed were impressive dynamic capabilities, at least when kept within it's operational boundaries. It can rock but one thing was clear. It was time to switch in more efficient speakers.
These came in the form of the recently reviewed HSU HB1 MK2 bookshelf monitors, augmented by a hefty HSU VTF3 MK2 subwoofer. Two things were immediately clear. First, this combination proved quite impressive combining an amazing soundstage with the ability to get pretty darn loud. It was also a little bright when combined with the MT-1 making this recording sound a bit bright for me. Measurements later in this review reveal that the rising impedance at the very top end of the frequency range starting around 2Khz causes a raising frequency response following the impedance bump. Long term, I found the combination to sound extra “special” with good recordings. Special isn't always a good thing as it sometimes indicates a problem that starts to rear it's head over the long haul. Long term, the HSU HB1 MK2 speakers were outclassed and replaced by the other set with the flattest impedance of the bunch, leaving me wishing for more power once more.
At the Rock Mountain Audio Fest, I was lucky enough to catch the Fry Street Quartet more than once. I really enjoyed their performances and felt compelled to pick up a recording of them. This CD did not have the same songs they played in Denver but their sound was still there. The recording has a rather dynamic sense of energy and good sense of space that the Xindak MT-1 reproduced with faithful verve. The second song on the second disk particularly comes to mind. Note that I listened to this on two channel SACD.
Diana Krall has become a bit of a cliché among some die hard audio purists but I proudly admit to being a fan. I love her smoky voice as well as the instrumentation in most of her recordings. One song that particularly struck me was “Temptation” when played over the MT-1. The decaying echo of the drums and cymbals as strikingly airy and real sounding. The bass was clearly little slower and richer than with the solid state amps when playing this release. It had a strong sound do it as if the amplifier was seemingly much more powerful. I played it for a friend of mine who didn't believe that the amplifier only had 12.5 watts per channel. Had I been playing with less efficient speakers, the outcome would likely have been different.
Input from Others
When my friend Arturo heard my system with the Xindak MT-1 in place, he commented on how open and airy it was. I have to agree. It creates a sense of air and space very well. Dr Hsu from HSU Research happened to stop in and commented that it seemed to have ample power at the level we were listening at and that it was nicely quiet without hum or hiss. I agree that it was able to reach decent listening levels with his speakers and that it was surprisingly quiet.
I decided to measure the frequency response of two of the speakers used in this review in an effort to explain why the impedance is so important with a tube amplifier. I measured with a solid state Bryston B100 SST and then measured with the Xindak MT-1 in the exact same position and input signal. The impulse response was shortened such that frequencies below 200Hz were not applicable. I did that to try and be as accurate as possible in the midrange and treble by further reducing the effect of room reflections. Smoothing was employed and 512 data points per line were taken. In all cases, the very top end of the spectrum was rolled off a little bit. The cables used during these measurements were the Canare 4S-11 speaker cables and Blue Jeans 1505F interconnects.
This first measurement is of the mini monitor using the SEAS L15RLY midwoofer and SEAS 27TDFC with a simple second order crossover and a special notch filter for the metal cone spike. The yellow line is the frequency response through the Bryston B100 SST and the red line is the frequency response when going through the Xindak MT-1. This was through the 8 ohms taps. Using the 4 ohm taps lessened this effect to about half of what you see here but it still was not enough. As you can see, this speaker was not able to be used when auditioning the amplifier.
Here is the impedance curve of the same speaker. Note how the impedance bump lines up with the rise in the frequency response.
Here are the same set of measurements when using the HSU Research HB1 MK2 speakers. The red line is going through the tube amplifier. I had noticed that it was pretty bright when listening but was surprised at the actual effect. It was even brighter than expected. I think part of that is due to different causes of what we perceive is bright or having too much treble. In this case, it was less annoying than one would expect as it was so clean. Sometimes an etch to the sound can make things sound bright when they really aren't. There was no etch to the sound via the MT-1, just pure liquidity.
Here, follows the impedance curve of the HSU HB1 MK2 speakers. Note, again, how the rise in response lines up with the rise in frequency response.
The above measurements should serve as an educational tool for those interested in the Xindak MT-1 integrated amplifier. Note that one speaker, in house, had a very flat impedance curve and worked great with the Xindak. Whether other tube amplifiers will follow this same observation exactly is beyond the scope of this review but, in my experience, they have.
The mighty little Xindak MT-1, at 12.5 watts is recommended but only for a very select group that meet this specific criteria in order to be overwhelmingly happy with it. Not meeting any of this criteria is a recipe for a let-down.
Your speakers should be at least 90db efficiency in a normal to small room or even greater in a large room.
You do not listen at ear splitting levels.
Your speakers have a flat impedance curve, especially through the critical midrange. If the impedance curve looks like a roller coaster, look elsewhere.
You don't need to have a remote control.
Those that meet this criteria are in for a special treat. To find the best dealer near you, I suggest contacting Lotus Audio Import.
Personally, I loved my time with the Xindak MT-1 but ended up sending it back because the speakers that work the best in my listening room have an impedance curve with two large bumps in the midrange. The speakers that worked the best with the Xindak are both serving duty in other rooms where a remote control is necessary.
Xindak MT-1 integrated tube amplifier
Bryston B100 SST
Forte Model 5
HSU HB1 MK2 speakers
Several pairs of DIY speakers
Kimber 4TC speaker cables cables
Canare 4S-11 speaker cables during measurements
Blue Jeans LC-1 interconnects
Blue Jeans 1505F interconnects during measurements
Dayton sand filled metal speaker stands
Hospital grade outlet from PS audio
Volex shielded power cords.
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