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Reviewer: Steve Marsh
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)
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.]

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.

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.

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
Manufacturer's website
US importer's website
Canadian importer's website