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Audio Space Acoustic Laboratory Ltd.
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Reviewer: Steve Marsh
Downstairs
Sources: Nottingham Analogue Mentor turntable with 10" Anna tone arm, Roksan Shiraz cartridge, Vecteur D-2 CD transport, Audio Note DAC Kit 1.2 with upgrades (PS choke, tantalum resistors, Black Gate caps, copper grounding bars on digital chips wired to central ground)
Preamp: Hovland HP-100 MC tube preamplifier, fully updated
Power amp: Red Rose Model 2A Silver Signature tube amplifier
Speakers: Audio Physic Anniversary (SLE) Step, Audio Physic Luna active subwoofer
Cables: Harmony Audio, Stealth Audio CWS, Music Metre Fidelis, homemade twisted pair of mil-spec silver cladded multi-strand copper
Power Cords: Analysis Plus Power Oval, PS Audio Mini Lab
Power Conditioner: PS Audio P300
Equipment rack: Michael Green
Room dimensions: 29" long x 16" wide x 10" high (sunken living room with open floor plan, long-wall setup)
Upstairs:
Sources: Thorens TD-125 Mk.II turntable with SME 3009 tone arm, Garrot P77 mm cartridge, Cotter Verion phono cable, NAD 5000 CD Player
Preamp: Slagle TVC
Amp: 6B4G triode-modified Dynaco ST70 tube amp
Speakers: original JBL Century L-100, Bastanis Prometheus Mk. II [on review loan]
Cables: Baton, TARA Labs RSC Prime, Cardas Golden Cross, Baton, WHG Grand Revelation
Equipment Rack: Stand Design 5, vintage wood equipment rack
Room dimensions: 22" long x 17" wide x 10" high, with eaves
Review Equipment Retail: $3,690/pr
Audio Space is a newcomer to U.S. shores, being imported by Mr. Alfie Lew of Gini Systems. According to fellow moonie Paul Candy, Audio Space is already quite established in Canada. Mr. Lew's website is well designed and describes the company as follows:
"Audio Space was founded at the beginning of the 90s with an original design and manufacturing facility in Hong Kong. It was the first reputable tube amplifier designer and manufacturer in the Greater China region. Today, Audio Space is the top high-end tube amplifier designer and manufacturer in Asia. The company is based in Hong Kong, with its engineering and design facilities local and its manufacturing facility in mainland China. Both are run and managed by a team of seasoned professionals from Hong Kong headed by founder Peter Lau." [Images from Hong Kong show below - Ed.]
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For review, Mr. Lew supplied the Audio Space AS-6M (300B) PP tube amps, one of six Audio Space amplifier models he carries. The full lineup includes 2A3, KT88, 300B and 845-equipped units. My amps were supplied with a prerelease instruction manual since the final manual was not ready yet. The amplifiers produce 21wpc and have an input impedance of 100Kohms. Mr. Lew thought they would be a good match with the JAS Orior speakers he supplied for an earlier review. Hopefully, the amps would also satisfactorily drive my Audio Physic Step SLEs.
As you can infer from the amplifier's name, these amps are push-pull monos utilizing the legendary 300B triode. Back in the late 1980s, the Western Electric 300B was at the vanguard of a return to triode tube amplification in the United States. Jean Hiraga had written an article about this valve in the French magazine La Revue Du Son and the Western world began to take note - again.
My own experience with the 300B began in 1988 when friend Arthur Loesch coaxed me into driving the 3.5 hours to his house and hear his personal 300B amps. He had read Jean Hiraga's article and built his own SE 300B amps using Western Electric tubes exclusively. The sound at his house was like nothing I had ever heard before and for me marked the beginning of a new direction in audio. I was astonished by the resolution and soundstaging while listening to some prime RCA shaded dogs.
In these early days of the American 300B renaissance, single-ended DIY designs ruled the day. Custom builders fed a growing underground demand. The only commercially available directly heated triode amps in the U.S. market then listed in the Audio Annual Equipment Directory were push-pull designs made by British company Audio Innovations. Their First Audio and Second Audio amps were something special, especially the later version of the First which used 6DJ8s in the input and two 6B4Gs per channel. (The Seconds were paralleled push-pull with four 6B4sGs per side). An acquaintance of mine still uses a pair of the Firsts with some power supply upgrades to great relish. Unfortunately, Audio Innovations went out of business.
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The underground buzz about SETs finally began to spill over into the mainstream audio press. VTL's Dave Manley, initially critical of single-ended designs, challenged the audio community with an amp that was switchable between single-ended and push/pull 300B operation. By 2006 today, there's an abundance of commercially produced 300B tube amplifiers as well as many current manufacturers of the tube: Cetron, Sovtek, Svetlana, reborn Western Electric, Shuguang (Valve Art), Electro-Harmonix, TJ Full Music/Sophia, KR Audio, Emission Labs and Euro Audio Team. Still and for purists, the original engraved lettering base WE 300B remains king.
Designers and DIYers alike still revere this king. However, they have now also scoured the annals of triode tube history with commercial and DIY triode amplifiers based on triodes all the way down to early radio output tubes (e.g., 71A, 10Y). Throughout these expansions into different tube types, the 300B has withstood the test of time while gaining some detractors along the way. Many have come to prefer the 45, the 2A3 (and its variants, the 6A3 and 6B4G), or the high-powered transmitting triodes (the 845, 211, 833, 811 and other European power triodes). Some have opined that the 300B tube is inherently weak in the bass. One thing that can be said is that it's an electrically highly linear tube.
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Audio Space supplies matched Shuguang 300Bs (standard brown base, metal plate version) and Shuguang 6SL7/6N9P and 6SN7/6N8P input and driver bottles. Rectification is solid state. I inquired about the circuit design in general terms but only got back that the 300B output tubes are run at a plate voltage of 378 volts. Parts seem to be selected with care ? the copper wire is from Italy, the silver/Teflon wire from the US, the volume pot a Japanese Alps, the DC filter caps Japanese Nichicon issue and coupling caps and selectors high-end audiophile-grade OEM parts from Taiwan. All transformers and coils are "hand-wound in house with proprietary technologies".
You can see much of the above in the underside of the amp. The two large Nichicon filter caps are 330uF/500V. There is a small circuit board for the bias adjustments but otherwise, hardwiring dominates. Coupling caps are polypropylene film types and labeled "Audio Space, for High-End audio'. Resistors are metal film. Tube sockets are ceramic. The power supply is choke-filtered.
As of this writing, a number of parts upgrade options are being considered. The possible upgrades include oil caps, carbon-oxide resistors, Teflon tube sockets and solid copper/silver wiring. These upgrade options will be posted on Mr. Lew's website when available. Aesthetically, I find the amps attractive. Build quality is high. Nothing's cheesy here.
The faceplate of each amp sports two toggles and two rotary knobs. One toggle sets the desired feedback level (0 or 3.5dB), the other selects between direct or line input. The line input inserts the volume control, the direct input bypasses it to turn the monos into standalone amps. The rotary knobs are for on/off and volume.
On the back of each amp are 0, 4 and 8-ohm taps, an IEC power inlet and four RCA input jacks. One pair of RCA inputs is labeled 1 and corresponds to the direct and line inputs. The other pair is labeled 2 and identical to 1. I ignored it until near the end of my review when I asked Mr. Lew for an explanation. His answer surprised me: "The extra RCA input jack for each of the direct and line function is for bi-wiring between preamp and amp. I know it's rare but that's the intended purpose. Just like biwiring loudspeakers, the effect is controversial. The option is there for the users who want it." That's a new one on me!
According to Mr. Lew, the amps were already broken in so I was off and running upon arrival. Since the amps produce 21wpc RMS, I gave them an exploratory shot at my resident Audio Physic Step SLEs in the downstairs system. As I've stated before, the Steps are not an easy load to drive - 84dB sensitivity coupled to a 4-ohm impedance. Their owner's manual recommends 10 - 60 watts but my own experience has been that they really need about 35 or 40 watts minimum to come alive.
Not surprisingly, the Audio Space (AS) amps on their 4-ohm taps weren't up to the Step challenge. Bass in particular suffered. Mated to my 1970s vintage JBL Century L-100s (believed to be around 90dB sensitivity) in the upstairs system, the amps were much happier. Having tried quite a few tube amps with the JBLs, I have found that their 12-inch woofer is difficult to control with lower power (and lower damping factor) amps. Heavy bass passages can get confused with blurring between notes. My acid test for this is a CD I've used in past reviews, Bassology's The Feeling That I Get [RMCD-1024.] The standup bass player, David Chevan, plays with power and dexterity. To their great credit, the AS amps controlled the rambunctious JBL woofers as well as any tube amp I've had on them. That includes my mighty Red Rose Model 2A Silver Signature. Impressive!]
There was one troubling aspect about the sound - a generally uptilted tonal balance. I immediately yanked out the Shuguang 6SL7s and 6SN7s and commenced some serious tube rolling. Methodically replacing each type with a variety from my extensive supplies, I settled on nickel plate GE 6SL7s (vastly underrated in my opinion) and RCA smoked glass 6SN7s. This improved the tonal balance and added depth and air. Still not quite where I wanted to be, I did some Internet research on the Shuguang 300Bs. The consensus? The Shuguang 300B-98C (titanium mesh plate version) is said to be markedly superior. After a quick email to Mr. Lew, two matched pairs were on their way.
Shortly after the arrival of the 300B-98C, Mr. Lew asked me to set the bias for the new tubes at 1.2 volts. This is very easy to do with a digital multi meter, via inset bias control pots in front of the output tubes. The improvements wrought by installing the 300B-98C tubes were not subtle. The most striking difference was an increase in weight and body throughout the frequency range. The soundstage expanded too, with a welcome increase in midrange bloom. If I was ordering these amps, I would try to have them supplied with the 300B-98Cs. That's not yet an option but Alfie Lew affirms that he and his partners in China and Hong Kong will be considering it.
I also compared the amp in the 0dB vs. 3.5dB feedback settings and preferred no feedback. Perhaps the 3.5dB option would be superior in other situations but in my system(s), feedback flattened the soundstage noticeably, though there was a little more bass weight - not a worthwhile tradeoff in my book though.
The next day, I was getting together with two Connecticut Audio Society members for some experimentation and refining of a 6B4G triode-modified Dynaco ST70. I took along the AS amps and installed them in my friend's system on his Quad ESL-63s. Compared to his 6B4G amp, the Audio Space monos exhibited the same tilted up tonal balance I'd already noted. I know both amps should be considered too low in power for the 63s but both seemed to drive them within limits.
Returning home, I put the amps back on the JBLs and got into a K. D. Lang jag. After skipping around some songs on Ingénue, I put on Tony Bennett and K.D. Lang on A Wonderful World [RPM Records/Columbia 86734]. The second cut "La Vie En Rose" was wonderfully open and airy. It was becoming apparent that soundstaging is a particular strength of these amps. When the first notes of a good recording are played, the sound reaches out well beyond the left and right boundaries of the speakers. Even when no notes are played, you imagine yourself sensing the acoustic charge of the space beyond the speakers. This is a special quality that many amplifiers cannot convey.
A couple of weeks ago, I bought out the entire front end of a high-end stereo system from a friend of mine who has transferred his vinyl collection to computer. Hiding in the booty were three pairs of Cardas Golden Cross interconnects. I recall having these in my system back in the 1990s when they were a top dog in the interconnect world. I remember them as having very smooth and musical properties, yet they were very revealing at the same time. The one criticism (if you would call it that) was that the cables tended to be a bit on the warm side. In my present circumstance, I decided to replace the Baton interconnects with the Cardas.
Now the considerable strengths of the amps began to exert themselves. First, there was an immediate sense of low distortion, expected of 300B amps. However, unexpected was the tremendous authority these amps exert. Large-scale and complex works were handled with aplomb. The soundstaging and dynamic blockbuster of French Opera Highlights [Mercury Living Presence 432014-2] was explosive, with detail all the way to the back of the hall.
The Cardas interconnects went quite a ways towards ameliorating my tonal balance concerns. The highs were still more present than I'm used to but this added presence was only put into relief when I switched back to my 6B4G amp. Another traditional strength of the original Western Electric 300B tube is an astonishing amount of midband detail. Neither of the Shuguang 300BsI tried came close to the WE standard but there was certainly enough detail to satisfy. One area where the Shuguang 300B-98C may in fact exceed the original WE 300B is in body or density of tone and, apparently bass performance (with proper output transformer design of course).
With the arrival of the Bastanis Prometheus Mk. II review speaker pair, I could now try the amps on a fourth speaker after the Audio Physic Step SLE, Quad ESL-63 and JBL Century L-100. The Prometheus sports a powered woofer, so I could really only evaluate the Audio Space amps above approximately 150Hz. The very high 100dB sensitivity of the open-baffle Prometheus mid/tweeter array coupled to the highish 0.67 V input sensitivity of the Audio Spaces' direct input required the Alps pot-controlled input to match levels with the powered woofer. As you might expect, the attenuated input is slightly veiled and less detailed than the direct input. I would recommend getting a Slagle or other TVC rather than using the line input to eliminate the resistor pot from the signal path.
The midrange and tweeter of the Prometheus are dipole so the airiness of the Audio Space amps was exploited to their maximum. Tony Bennett and K. D. Lang now occupied an enormous soundstage. At first, I was captivated by this sonic landscape but in the end, I decided that the amps really mated best with the JBLs. The Prometheus is primarily designed for micro-power SETs. Both Mr. Lew and I were aware of this but I wanted to give it a go nonetheless.
As a final confirmation of my listening notes, I put the amps back on the JBLs and pulled out a few more CDs. One that really showed the strengths of these amps was Caribe! Caribe! on Putamayo [ PUTU 153-2]. The CD's introductory heading states "Join us on a Caribbean journey and party the night away." The throbbing bass of the Caribbean rhythms and the joy of the performers were conveyed with such verve that the invitation was hard to resist.
Prior to my concluding statements, please permit me to digress. Some time ago, there was a thread on Audio Asylum as well as a discussion amongst our team of writers, about the importance of system matching. The discussion (greatly simplified here) began with an inmate questioning the lack of negative reviews in the audio press. Srajan entered the discussion, pointing out the importance of system matching and that a manufacturer's product did not deserve to be declared inferior just because it did not shine with the reviewer's particular combination of components and taste. Some other 6moons reviewers, in our internal emails, agreed that it was unfair to criticize a component too strongly in a review since it may not have been given a chance to show its best with whatever was really its electronic soul mate - to use an anthropomorphism.
My own opinion in this debate is that I place a higher value on a component that can sound good with a wider variety of equipment. Of course, one has to take into account the obvious limitations of the design (e.g., flea-powered amps and power-hungry speakers) and mate them sensibly. However, within the context of mating equipment that should be able to work together, I value a component more if it sounds good with many different components and in many different systems. This is no great insight on my part but I don't believe this point was made in the discussion.
The reason I bring this up is because I believe it applies to this review. The Audio Space AS-6M (300B) PP monoblocks are not laid-back sounding amps. My inclination based on the positive sonic effects I've heard from installing oil caps and carbon-oxide resistors is that prospective buyers should investigate these options. As supplied, the amps require careful matching more so than most other amps I've tried or owned.
Overall, however, I can think of no other low-power triode tube amp that has provided my system with the expected strengths of triodes (purity, detail, low perceived distortion and high resolution) as well as the low-end control, cinemascopic soundstaging and authority of the Audio Space amps. Their combination of virtues is not easy to come by.
Steve Marsh |
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Enjoy the Music.com
NEW ADVENTURES in HIGH EFFICIENCY
Article by Scott Faller (Mid-August 2006)
Audio Space 6M-300Bpp
300B Push-Pull Monoblocks
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In this episode, my Adventures In High Efficiency takes me into the realm of amplifiers.
As you are well aware, there are scads of low(er) powered amplifiers on the market today. For this article I've chosen a relatively high powered piece of gear, the Audio Space 6M-300Bpp. As the name implies, this pair of monoblock amps are a Push-Pull design and use 300B's as the output tube. According to the manufacturers specifications, this pair of amps puts out 21 watts per channel. In the world of low power amps, that's huge wattage.
According to Alfie Lew of Gini, United States distributor of the Audio Space line, says "Audio Space with its full name Audio Space Acoustic Laboratory, Ltd. is a Hong Kong company that was founded back in the early 1990's before the British turned over Hong Kong back to China in 1997. It still headquarters in Hong Kong, which is now a self governed Special Administration Region (SAR) of China. Audio Space's manufacturing plant known as Corilex, is a separately registered business located in the Southern part of main land China. In Europe, Audio Space collaborates with a European company and have established a line of tube gear marketed in Europe under the name of Duntonic."
The Design
 The basic design of the 6M uses the 300B in Push-Pull configuration. After opening up the amplifiers it appears that the circuit topology is the standard ultra-linear. The input driver tubes chosen are the 6SL7 and the 6SN7. The good thing about the choices of driver tubes is that these tubes are readily available as new production or if you wish to tube roll, new old stock. Bottom line, your choices for tubes are very plentiful and relatively affordable depending on which route you take.
In talking to Alfie Lew he states that Audio Space get the cr鋗e de la cr鋗e of the Shuguang 300B tubes. They actually hand pick their tubes from the production line before Shuguang labels them with their own label. The Audio Space tubes are AC matched using a 1k frequency then hand picked to (closely) match mu (the tubes amplification factor). I use a pair of the Shuguang 300B tubes (supposedly lesser quality than the Audio Space tubes) quite often in my Welborne DRD's. I'm very happy with the sound of the Shuguang tubes and they regularly alternate time with my TJ Mesh Plates. They are just a tad brighter than the TJ's with just a bit less midrange fullness. They are a very nice sounding tube.
The 6SL7 and 6SN7 tubes are also of Chinese manufacture also from the Shuguang plant. Though you can get a ifferent' sound from NOS 6SN7 (and 6SL7), the Chinese tubes get the job done fairly well. I personally find them a bit brighter and harder sounding in my system than say my vintage Sylvania's but they aren't a bad sounding tube by any stretch. Although rolling tubes is not a must, to fine tune my system for this article, I used my Sylvania's. My Lowthers don't need any help in the treble department. The Sylvania's to me, just sounded more ight,' so I used them.
The potted transformers (power and output) used in the 6M are custom wound for Audio Space. In addition, it appears that the choke used in the power supply Pi filter is custom wound for Audio Space also.
 Power rectification duties are accomplished via solid state design using a standard bridge rectifier. The power supply is a CLC design with ample filter capacitance. Power supply filtering is provided by a pair of very nice sounding Nichicon NX series 300mF caps. The rest of the electrolytics in the Audio Space amps are also Nichicon's.
As an aside, the main power supply caps do not have bleeder resistors. Normally this isn't an issue unless you are an idiot and stick you bare hand inside the amp and then ground yourself (like I did). You soon remember that no matter how long a cap sits with no power on it, the caps may never completely discharge (until you touch one of them... zzzzzzZIT). One of these days you'd think I'd stop being over confident inside amps and I'd wear my linesman gloves that are rated to 6000 volts. Oh well, that'll learn me... (again).
 The driver (gain) stage is capacitor coupled to the output stage. The capacitors are metalized polypropylene (MKP), private labeled by Audio Space. The coupling cap values are .22 for those of you keeping score. According to Audio Space, metal oxide resistors are used in high voltage portions of the 6M's circuitry while carbon oxide resistors are used in areas of lower voltage. One item that the designer pointed out about this design is that the 6M's are equipped with an "auto hum balance" circuitry to keep hum noise to under 1mV. Supposedly with this feature, there is no need for a hum balance pot when rolling tubes. The designer believes this to be an industry first, though I can't say for certain. He claims that none of the other Chinese brands have it. Without giving too much away regarding this circuit, it consisted of a cap and a voltage regulator (if I reverse engineered it correctly). It did seem to do the job quite well as the amps were extremely quiet.
The Audio Space 6M uses a 'Class A,' Push-Pull approach. The amplifiers are operated at a constant 60mA bias current as opposed to 30mA to 40mA in a standard 'Class AB' design regardless of signal level.
The internal wiring on the driver stage is done with solid core silver wire with Teflon dielectric. The output stage utilizes standard copper hookup wire. As you can see, the internal wiring is very clean and compact. Critical interconnect wiring is tightly twisted to prevent unwanted transmission of EMF's and the like. The small PC board houses the interstage coupling and the driver tube bias circuits. Everything else within the Audio Space amp sports point to point wiring.
An interesting feature to this amp is the fact that it has switchable, negative feedback. One of the switches on the front of the unit allows you to apply a nominal 3.5dB of negative feedback to the circuit. It's actually a nice feature. In fact I added this modification to my big KT88 monoblocks some time back. This feedback switch allows you to do some additional fine tuning to your music.
Recent converts to the tube realm may find the addition of feedback a little more aurally pleasing since it (essentially) cancels some of the even harmonics that tubes are so noted for. The feedback circuit is said to add some tability' to the overall amplifiers performance. Feedback also increases the amplifiers bandwidth and can add a skoash of damping factor to the total design by lowering the amplifiers output impedance. All in all, feedback need not be a bad thing in all cases. That said, personally I'm not a big proponent of feedback. I'd rather have my music served traight up' just like my scotch, but that's just my opinion so take it for what it cost you.
Another cool feature of the Audio Space 6M's are the fact that you can either use these as a standard amplifier with a preamp or you can plug in up to two sources into the back of these units and use the integrated volume pot on the front of the unit. Switching between the two sources is accomplished by a simple rotary switch located on the left side of the faceplate of the unit.
As far as the cosmetics of the Audio Space amps go, these are very stylish looking. The main chassis is highly polish, heavy gage stainless steel. This means there is no possibility of rusting in a humid household environment. The front faceplate on the review samples is also polished with a raised black border. Just below the gold nameplate is a single, bright blue LED power indicator. The power and output transformers are cased in a glossy metal-flake black pot.
On the back side of the amps is the standard fare of gold plated RCA female jacks. The binding posts are nice quality gold plated brass with knurled tightening jacks.
Here is an item of note. As I read through the manufacturers instructions, I notice that the Audio Space 6M's are warranted for a full 24 month's. That a damned good warranty period for a piece of tube gear. The vast majority of competing manufacturers only offer 1 year. So much for the thought that Chinese gear is (or can be) inferior. A warranty like that gives me warm fuzzies.
Overall, I've found the amps to be very good looking and the build and parts quality to be exceptional.
A Brief Statement On Push-Pull vs. Single-Ended Topologies
To my ears a Push-Pull amp can suffer when the music sine wave is split into two inverted phases and then reassembled at the output transformer. Personally, I tend to hear some sibilance on vocals when amplifiers don't reassemble the two halves of the sine wave properly. When the topology is implemented properly, this issue can be nearly inaudible. With a single ended amplifier, there is no splitting of the sine waves, hence no reassembly issues.
The other item that I notice about Push-Pull amps is the soundstage. When I compare a Push-Pull amp to a Single-Ended amp, the soundstage on a Push-Pull amp is noticeably narrower. They tend to have a tight, focused sound. A good single ended amp has a cavernous presentation. Although the sound extends beyond the outside of the speakers, they still retain very good focus. A single ended amp also sounds open and effortless compared to a Push-Pull amp. These qualities too can be minimized on a quality Push-Pull design.
As I talk about the sound of the Audio Space 6M Push-Pull 300B's in this article, I'll be making comparisons to what I personally feel should be the benchmark to all other amplifiers, well designed, single ended triode amplifiers.
The Sound
Before I start describing the sound you need to know how my system was setup for this article. I decided to spend the vast majority of this review using my Lowther PM2A's as my main speakers. If any speaker is going to tell me exactly how an amp is going to sound, the Lowthers will. As usual, the majority of the time I used my 15" Goodman's to fill in the lower frequency regions where the Lowthers can't go. I did run the Lowthers full range and also ran my Goodman's (which are actually full range coaxial drivers) to evaluate the bass response of the Audio Space 6M's.
My source gear is (as always) is my heavily modified Korato KVP-10. My digital is provided via the Bolder Cable modified Squeezebox 3 being fed into the MHDT Labs Paradisea tubed DAC. My turntable is the Opera Audio LP-5 with the Dynavector 507 MkII arm with the DV-20XH. the cartridge is feeding my Graham Slee Audio Jazz Club phono stage. The entire system gets clean power from a DeZorel Audio Reference Senior line conditioner. The amps used for comparative purposes are the Welborne DRD 300B monoblocks and my Handmade Audio 2A3 Deluxe Classic.
Now for how the 6M's sound. The guys from Gini suggested that I go ahead and let the amps break in using the stock tubes. After the 100 or so hours of break in they wanted me to start my listening with the stock tubes before I started tube rolling. As expected the Chinese driver tubes sounded fairly decent on my Lowthers but when I rolled the Sylvania's in their place, everything became more to my liking. I kept the NOS tubes in for the balance of my time with the Audio Space Amps.
Lets start at the bottom and work our way up this go around. Since my Lowthers are ow frequency challenged' (that's a nice way of saying they don't do bass for squat), for this portion of my testing, I connected the Audio Space 6M's into my 15" Goodman coaxials. Since I have these speakers corner loaded, I'm getting pretty darned good bass out of them all the way down to the mid to upper 20's.
A couple of my favorite tracks to use for testing bass are Until the End of the World by U2 and nearly the entire album Peace Beyond Passion by Me'Shell Ndegeocello.
When you play U2's Until the End of the World on any stereo, its obvious that the bass is completely overdone. Its muddy, boomy and overall sounds pretty bad. So what better way to find out how the 6M's control what is uncontrollable bass. As I played this track I have to say that I was pretty impressed. I half expected the 6M's to roll over and play dead, but they didn't. Even when presented with an extremely difficult recording like this one, they held their own. Not quite as good as a solid-state amp but that is a horse of a different color. The 6M's kept very good control on my 15" Goodman's.
Bass player Me'Shell Ndegeocello from Peace Beyond Passion has some killer bass tracks on it. The opening songs called "The Womb and The Way" are a true test for bass control and accuracy. I'm happy to report that the 6M's passed with flying colors. The bass stayed tight, fast and clean through the entire song which can act as a real torture track especially at the high volumes I was playing it at.
And of course I used my usual rounds of acoustic bass both plucked and bowed. For the plucked I used some Ray Brown from Some of my Best Friends are Trumpet Players. This is just good music, no matter how you slice it. Ray puts on his usual stellar performance on the bass which shows no signs at all of sounding slow, soft or mushy on the Audio Space 6M. Each note stayed as true and concise as when it was played.
Since I've got Ray Brown's disc spinning, I may as well roll right into the midrange sound of these amps. This particular album can easily be used as one of your reference CD's, the recording quality is so good. In turn, the recorded trumpets can sound extremely lifelike with the right amps and speakers. When I compare these tracks on the 6M's to my Welborne DRD's the 6M's come pretty darned close to the clarity of the DRD's but they do fall just a tad short. Speculating, it's the coupling capacitor. I don't think it's a quality issue as much as the DRD's are direct coupled which eliminates that coupling cap. It's not really a fair comparison but I have to use (what I feel) is my benchmark for clarity. That said, I've listened to enough capacitor coupled amps to say unequivocally that the 6M's do an exceedingly good job on midrange clarity.
As I moved onto some female vocals, namely Alison Krauss and Union Station, Alison's voice came through with a clarity and presence you don't often hear in capacitor coupled tube amps. Though is wasn't as clean as the direct coupled Welborne DRD's, it was extremely close. The best part was I didn't notice any significant coloration. All too often, a designers choice in parts can lead to an unnatural coloration of the music. That isn't the case with the 6M's. It's obvious to me that the designer experimented with the parts to find that ight' combination of naturalness and transparency.
All of the great things that I'm hearing in the midrange transfers directly to the high frequencies. Since Audio Space has found that magic combination of parts and design, the highs present themselves just as cleanly as the midrange. In all my time with the Audio Space 6M's (and a significant amount of time it was), I never once found myself having listeners fatigue. As I mentioned early on, I rolled the Shuguang driver and inverter tubes out for some NOS Sylvania's. In my system and to my ears, these tubes sounded better. The highs came through without a hint of glare or etching. The shimmer of cymbals, the ultra high harmonics of things like triangles lent themselves perfectly to the ir' surrounding any performance I listened to.
One of the final things I listen for is sound staging and imaging. As I mentioned earlier, Push-Pull designs can be a bit of a compromise when directly compared to a quality single ended design. The Audio Space 6M is no different. Since it is a relatively standard Push-Pull design (read = not a constant current source), you will find that that the soundstage does remain narrower than that of a really good SET. That is not unexpected in the least by me. In fact, this pair of amps actually does quite a good job of projecting themselves based on the type of design.
My usual test for this is Pink Floyd's "Sounds of Life" from A Momentary Lapse of Reason. The water lapping on the shoreline that is projected by the Audio Space 6M's comes from about 4 feet outside of the Medallion's cabinets. That's pretty impressive for a Push-Pull amp though not quite on par with my DRD's.
When it comes to imaging, these amps do a great job reconstructing the performers on a virtual stage. The performers take on very realistic proportions. The amplifiers effortlessly place each instrument and performer without any significant smearing of the image.
Comments About Speaker Matching to Low Powered Tube Amps
Please, don't let what you're about to read, scare you off because it shouldn't. If you've never owned or operated a low powered, high efficiency speaker combination, these are a few of the things you need to be aware of before you dive headlong into this area of what I consider the best sound on the planet. Look at it this way, if you were going to the Caymans to scuba dive, wouldn't you take some lessons before you strap on a tank, jump in the water and start sucking on your regulator?
All too often I see people write that they didn't get the uality' of sound they expected when they listened to a low powered amplifier. They claim they heard slow sloppy bass, poor image reconstruction or even a tilting of the tonal balance. The trouble with these comments (more often than not) is that they have tried to mate a low powered tube amplifier that has a miniscule damping factor to the wrong speakers.
If and when you decide to get into the world of tube amps, it doesn't matter if it is a Single Ended Triode or some huge multi-tube behemoth like the Audio Research Reference 610T, you must pick the correct speakers to mate to these amplifiers. You can't go out and pick any old set of speakers and expect them to work well with a tube amp. You need to do some homework first.
You need to know that just because a speaker claims high efficiency does not mean that it will work with a tube amp that has a low damping factor. There are a number of igh efficiency' speakers on the market that pose too great of load for an amp with low damping factor. Remember, tube amps provide ample voltage at very low current. Solid state amplifiers provide tons of current which (in turn) puts a strangle hold on a pair of speakers.
Certain line arrays and some speakers that are designed using higher efficiency drivers and even some prototypical vented enclosures have been known to give a tube amp fits. And finally, let us not forget, just because a speaker has a Klipsch, JBL or an Altec label, does not mean that it automatically will work with a tube amp.
Second, a tube amp that sports a Push-Pull design, does not automatically mean that the amp has a large damping factor. In order for a tube amp to perform well, the speakers impedance response must be reasonable. Huge swings of impedance at a speakers Fs (resonant frequency) that go much above 40 (or so) ohms or that dip below (say) 4 ohms can spell disaster to the overall sound of the lowly tube amp that has a damping factor in the single digits. Additionally, large impedance swings can take place at the crossover points between the speaker drivers. These too can negatively effect the sound of what would otherwise be a perfectly fine sounding tube amp. When you (improperly) match these type speakers with a tube amp, you are asking for slow, sloppy, vague, undefined sound.
One of these days I'll take a stab at an article devoted specifically to mating speakers to tube amps. In the meanwhile if you are looking for an excellent primer on high efficiency drivers done correctly, I'd like to suggest James Melhuish's site, the Single Driver Website. There, James has assembled not only information on full range drivers but also horns and tons of DIY projects. You can register and post questions on his Full Range Driver Forum. You also have the option of going to the Audio Asylum's High Efficiency Speaker forum, the Bottlehead forum, the Decware forum or a number of other web forums and ask questions. Don't be bashful. The vast majority of these guys can be very helpful and are very tolerant of the ewbie' to high efficiency realm.
And finally, if you are brave enough, surf over to the late, great Harvey izmo' Rosenberg's website and sift through the Triode Guild articles. Though Harvey was completely mental in his writings (in a good way), he was absolutely spot on. This guy was so ight', its almost scary. Read all of his articles you can about speakers. You'll spend a fair amount of time digging but you'll get to have a good laugh and get educated at the same time. Harvey was one of my favorite writers. I miss him. He explains tube amp to speaker matching much better than I do here. Let me suggest Into The Heart of Speaker Darkness is a good starting point.
Repeat after me, Alnico...
So In The End?/font>
I can say without reservation that the time I spent with the Audio Space 6M 300Bpp was thoroughly enjoyable. The additional headroom this Push-Pull design provided was a welcomed addition to my system.
I found the sounds that came from these ultra-cool looking monoblocks to be very good. The 6M's presentation was clean and clear. Though sometimes lacking in lesser amps, the midbass reproduction coming from the Audio Space amps were more than ample for my Lowther PM2As. The highs were clean and extended without ever coming across as being right'. For those of you pushing big woofers, the low end is just what you'd expect from a quality Push-Pull design using very good transformers.
When it comes to Audio Spaces choice of using solid state rectification, I'd have to say it is pretty much a non-issue. Although tube rectification has its advantages, a well designed solid state power supply can sound very good, as it does in the 6M. The other plus is you don't have to worry about oosing' a rectifier tube and taking out half of your power supply.
As I look at the surrounding competition of the Audio Space amps, the 6M's fall towards the bottom of the pile when it comes to pricing. Considering the quality of parts, the solid design, the amplifiers aesthetics and finally the sound, frankly, I'm quite surprised. The vast majority of their competition is almost double and in some cases triple their cost. A quick Google search on a "Push-Pull 300B amplifier" brings up some rather large industry names, most of whom are considerably more expensive. Remember in this business, more money does not necessarily equate to better sound. More often it only means ifferent' sound, and as we all know, sound is a purely subjective issue.
When all is said and done, I personally found the Audio Space 6M 300B pp amplifiers a true joy to live with. The slight reduction in soundstage when compared to a single ended triode design didn't diminish my thorough enjoyment of the amplifiers at all. Their resolution was very good. So good (in fact) that I didn't long to put my DRD's back into the system, and that's saying something.
The other item I really enjoyed was the drastically increased headroom their 21 watts gave me. Never once did these amps run out of gas with my Lowthers. As many of you know, when you feed Lowthers some serious wattage, they can really come alive. They show exactly what they are made of. The dynamic peaks and infinite detail I experienced with the Audio Space 6M's will defiantly be missed.
So, if you are in the market for a fine sounding Push-Pull 300B, you likely won't go wrong with the Audio Space 6M's. Properly mate them with the right speakers and you'll likely fall in love with these amplifiers. They are well worth checking out.
My Ratings
Please keep in mind this rating system is used to compare the Audio Space 6M 300B's against absolute perfection, or a money no object PP design. If you see what you think may be a low(ish) score, it's because there are PP 300B designs that are even more refined but consequently cost considerably more. To top that off, if I assign 5's across the board, I've just painted myself into a corner leaving no room for that ltimate' amplifier. You won't see me handing out many 5's. In turn, I feel I need to leave room in the ratings system to accommodate those amplifiers.
Tonality |
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Sub-bass (10Hz - 60Hz) |
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Mid-bass (80Hz - 200Hz) |
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Midrange (200Hz - 3,000Hz) |
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High-frequencies (3,000Hz on up) |
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Attack |
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Decay |
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Inner Resolution |
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Soundscape width front |
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| Soundscape width rear |
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Soundscape extension into the room |
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Imaging |
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Fit and Finish |
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Self Noise |
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Value for the Money |
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Specifications
Type: Stereo integrated amplifier
Tube Complement: two 300B. one 6SL7 and one 6SN7 per channel
Output Power: 21 wpc
Frequency Response: 20Hz to 20kHz (+/-2dB)
T.H.D.: <1%
Output Impedance: 4 ohm or 8 ohm
Input Sensitivity: 300mV/LINE IN, 670mV/DIRECT IN
Input Impedance 100Kohm
Signal to Noise Ratio: >87dB
Dimension: 470 x 180 x 195 (DxWxH in mm)
Weight 15kg each unit
Price: $3,690 per pair
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