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POSITIVE FEEDBACK ONLINE - ISSUE 24
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audio space

6M-KT88 amplifiers

as reviewed by Ed Morawski and a bit or two from Dave Clark

(photos and such by Dave Clark)

 

 

 

ED MORAWSKI'S SYSTEM

LOUDSPEAKERS
DIY with Scan Speak 9700 & 8535 Drivers and Series Crossover or Magnepan MMG with modified crossover and stands.

ELECTRONICS
Musical Fidelity A308 power amplifier and a BAT VK-3ix preamplifier.

SOURCES
Musical Fidelity A308 CD player (used as a transport), a Tri-vista 21 DAC, and a Roku M1000 SoundBride Music Server.

CABLES
Empirical Audio interconnects and speaker cables, Stealth XLR interconnects, Analysis Plus Oval 9 Speaker cables, and Cardas Cross XLR interconnects

ACCESSORIES
DIY Flexy rack of plexiglass, dedicated circuits with Brick Wall surge suppression, Balanced power transformer feeding the CDP and Acoustic First foam panels. Vibrapods, Herbie's Magic Feet and good old hockey pucks. Stillpoints ERS paper

 

The Audio Space 6M-KT88 monoblock amplifiers are a push/pull, Class AB design with many unique features. Aside from the ability to switch between ultralinear and triode modes, they are equipped with volume controls to allow direct connection of sources like CD players. Each amp has two RCA inputs, one of which bypasses the internal pot and the other of which is connected via the volume control, allowing many different equipment configurations. The front-end utilizes a 6SL7 for input/gain and a 6SN7 for buffer/driver and phase inversion. The amps are available with either 300B or KT88 output tubes. I had the KT-88 model.

The 6Ms are designed to emphasize the sonic characteristics of tubes. Audio Space encourages tube rolling, allowing users the flexibility of experimenting with tubes of different makes. The manufacturer claims that the sonic differences will be pronounced and immediate. A selector on the front panel allows the user to switch between operational modes. I preferred running the amps in triode mode, as this provided a slightly more musical sound. Most of my listening was in triode. The AS-6Ms feature point-to-point wiring and hand-wound transformers specially made for them. According to Audio Space, the circuit is designed with "true balanced" capability that will be implemented in a new model in the near future.

Information on the AS-6Ms is a little hard to come by, since the US importer's website (www.gini.com) does not give any information about them, and the manufacturer's site only provides specs and pictures. Even then, the specs are missing several key values, and the owner's manual is light reading. I can only report what is listed, and what I know from experience. The specs I could find for the AS-6Ms state:

  • Output power: 50W (ultralinear), 25W (triode) into 4 or 8 ohms at 20Hz-20KHz with <1% THD

  • Input impedance: 68Kohms with S/N ratio of >89dB

  • Output impedance: 4 or 8 ohm s (via separate binding posts)

  • Frequency response: 20Hz - 20KHz +/- 0.5dB

  • THD: <1% 20Hz - 20KHz (ref. output)

  • Signal-to-noise ratio: >89dB (hum/noise <1mV)  

  • Tube complement: 1 x 6N9P (6SL7 or ECC35), 1 x 6N8P (6SN7 or ECC32), 2 x KT88

All in all, pretty decent specs. The AS-6Ms are certainly easy on the eyes, with their bright chrome-plated chassis and knobs. The workmanship is first rate, and the amps look more expensive than their retail price of $3290 per pair. I did have to consult the manual several times while connecting them since there are so many inputs, outputs, and controls. The amps are unusual in that the two chassis are mirror images of each other. That means that you have to look carefully, as the volume controls are at opposite ends. In my dim room, I found myself constantly getting the power knob and volume knob mixed up, but I like the design as it gives the units a balanced, symmetrical look. You also need to remember that the inputs marked "Direct" bypass the volume control, while the ones marked "Line" pass the signal through the volume control. This makes sense, since "Direct" could mean "direct from a source," but "Line" could mean "connected through a line preamp," while in fact it means that the amp acts like a line preamp.

Other than their appearance, the first thing I noticed about the AS-6Ms was how quiet they were. There was no hum or noise of any kind—no tube rush, distortion, or microphonics. The amps were completely trouble-free during the review process, a glowing achievement considering the fact that they are limited-production, hand-wired tube amplifiers. The other components I used during the review period consisted of my Balanced Audio Technology VK-31 preamp, a Musical Fidelity A308 CD player feeding a Musical Fidelity TriVista 21 DAC, and my Olympic Audio OA-1 speakers, all connected with VooDoo Reference series cables.

The AS-6Ms have all the benefits of monoblocks, including better channel separation, a wider soundstage, and minimal crosstalk, thus a more quiet background. The AS-6Ms sounded bigger and more refined than their 25-watt-per-channel specs would indicate. Granted, I have a small room, but the amps filled it to capacity, with no sense of strain. I enjoyed their sound immensely. They were very detailed, with a slight but pleasant bloom from about 300 to perhaps 5000Hz. Strings sounded especially good, as did both male and female voices. Bass was abundant and well defined. While the AS-6Ms had good control of the low end, they did not match the iron grip of my Musical Fidelity A308CR, but their bass was very easy to live with. I often use Keiki Matsui's Deep Blue as a bass test. This disc can sound uncontrolled and very bloomy when heard through an inferior system, but the AS-6Ms passed the test. Although they didn't grip and hold on like an 800-pound gorilla, not one bass note escaped their control. I tested the other extreme with my current favorite recording, Mirabilis , by the Mediaeval Baebes. This CD, which features a female chorus, also sounded very pleasant. I especially liked the track "Temptasyon," on which the Baebes sounded very airy and dreamlike.

While my reference map, the Musical Fidelity A308CR, is slightly more transparent and detailed, the AS-6Ms had nothing to be ashamed of. They are among the best tube amps I've heard. The Atma-Sphere M60 Mark IIs are better, but not by much. Those are my favorite tube amps, but I could live with the AS-6Ms, and they are certainly better looking.

I listened to all of my favorite recordings, and in not one case could I find anything to complain about. I enjoyed every recording I played, and never found myself wanting more. It is the rare component that doesn't possess compromises, but I could find no fault with the AS-6Ms. I played with all of their controls, inputs, and outputs. trying many combinations. Although the impedance of my speakers is nominally 6 ohms, they sounded better when I used the 8-ohm taps. I wasn't able to hear any change in volume with the 4-ohm taps, but the amps had a more pleasing musicality when I used them at 8 ohms.

I tried the ultralinear mode several times, and although the differences were very subtle, I always preferred the triode mode for its smoothness and its ability to convey nuances. While the ability to bypass the preamp seems to be all the rage these days, I have a thing against passive preamps and direct connection of sources to power amps. I usually find the results flat and lifeless. Because they are tube amps, and despite my prejudices, I thought the AS-6Ms might work well this way, and indeed they did. For once, the life wasn't sucked out of the music! I still preferred them connected through my preamp, but I could easily live without the preamp in a pinch. The budding audiophile could start with the AS-6Ms, add a good source, then add a preamp.

I feel obligated to reiterate how unbelievably quiet the AS-6Ms were. I have heard many solid-state amps that (unfortunately) had more background noise. This is a real achievement that, I think, speaks volumes about the quality of Audio Space's design and production capabilities. The Audio Space 6Ms produced nice tone that was a bit on the warm side (as is usual for tubes). They produced a good soundstage, with good imaging and very good detail, and they had great bass. Couple this with their excellent workmanship and great looks, and I think you have a winner. They represent a real value in the audiophile market place. In this crazy world of $350,000 amplifiers, there are still good values to be found if you know where to look. I suggest that you take a good look at the Audio Space 6Ms. Ed Morawski

 

Some Additional Comments from Dave Clark

Ah, yes... another product from China ...and very nice one too! Which is not to suggest that Chinese products are not nice, or can not be nice (no doubt there are, just as one can find from any other country) ...but these little amps from Audio Space are VERY nice for the money. Audio Space is a veteran Chinese electronics manufacture with a good 20+ years of experience. Meaning that they are not some upstart but have a decent history in the East for making quality audio products for the Asian market.

I had the AS-6Ms in my system for a week or so prior to Ed and in reading his take here, I find that there is not much for me to add―he hit the nail right on the head! So let me say this ...in my system the amps played well with others offering a big musical sound that belied their wattage. The amps rocked. And they did so with an abundance of musical enthusiasm.

While they are not the last word in detail, they will let the music across with very little editing―that is, they are more forgiving than analytical; which in my world is always preferable. Hey, they are lowish-powered tube amps for chrissakes!

Additionally, they play with a bigger ballseresy bass that is perhaps a touch too much at a narrow frequency range―almost like a subtle loudness contour that could be heard to a greater or lesser degree on all my music. So reader take note. They do have (at least here) a slight bass emphasis that in some systems may just be the cat's pajamas, though in others it could be the dog's trousers (what is the opposite of the cat's pajamas anyhow?). I did not find it to be an issue either way as my system is already full-range, but truth be told, it was audible.

Very nice indeed. No problems playing loud nor playing for extended periods of time. Dead quiet, easy to use, pretty much plug and play, easy on the eyes and ears, and not a load on the pocket book. Give them a listen.

I would add that the Audio Space line includes what looks to be different versions of this amp based on other tubes. Visually quite the same ...interesting.

6M-KT88 amplifiers
Retail: $3290 a pair

Gini Systems
web address: www.gini.com

Ed is currently involved in the manufacturing of Olympic Loudspeakers.

 

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