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Audio Space 300B Tube Amplifier
Audio Space 300B Tube Amplifier Series

(Hi-Fi Review Dec 2004, p. 194-198)

Since the "300B amplifier contest" (Vol. 205), I have done what I always wanted to do. While having satisfied my craving, I have also obtained much advanced knowledge about the function of 300B.

As time passed by, I once again became interested in 300B amplifier. Last time, I put 6 different types of 300B amplifiers together for comparison, and this time I would like to test 300B amplifiers of the same brand but of different models.

Several brands popped into my mind when I was about to play this game: 1) Dignity Audio. Though their 300B amplifiers have unimaginable power, there is not much differentiation between two models of this brand --- cheapest one (price at HK$50,000) and expensive one (price at HK$90,000) in terms of the design concept as well as the sound preference. Hence, there will not be much fun for comparing them simultaneously. 2) Audio Note. They have many 300B amplifiers while Meishu Line Signature is a very good integrated one which I have auditioned before. They also have more than 10 models of power amplifier ? some of them are equipped with 1 pc of 300B for each channel whereas others are equipped with 2 pcs of 300B, and they also use different portion of copper and silver. If they can be put together for comparison, that would be very interesting and magnificent. The only problem is that such kind of expensive amplifiers which cost HK$100,000 to HK$200,000 will only be available through import upon order confirmation by customers, while on the other hand, the relatively cheaper ones which cost less than a hundred thousand are always out of stock. Hence, it is still not the right time to have this brand. 3) Audio Space. There are three models of 300B amplifier using the two different trademarks - "Audio Space" and "Duntonic", and every one of them are very different in terms of their design concept, sound, characteristics and usage. Another important point is that their retail prices are very economical and practical. Report on the comparison of these amplifiers is not only interesting but also providing some guidelines to the potential buyers to make the selection wisely. With the permission by Sam Ho and Mr. Lau (boss of Audio Space), I therefore started to play this game. I was delighted to share with the readers such experience and in the meantime I could also satisfy my own cravings.


Audio Space has developed many models of 300B amplifiers. According to my knowledge, the early two models put forward by Houston were TTP300A-81S and M. Many years ago when I was just getting to know them, they had AS-9023 and AS-9813. As time passed by these models had already ceased production. They were then replaced by the first version of AS-300B, which was introduced to the market in October 2000.

As-300B is an integrated amplifier that can also be used as pure power amplifier. Each channel is equipped with 1 pc of 300B as single end Class A power amplifier, providing the power output at 8W. This is the first integrated amplifier manufactured by Audio Space that uses 6SL7+6SN7 and remote volume control. It is also the first product formally adopting 300B tubes. It is manufactured under the request of Mr. Inoue, the Japanese acoustic expert, and it is also a long-lasting masterpiece.

Three years after AS-300B came out, the MKII was produced in February, 2004. It shifted the RCA terminals (totally, there are two pairs of output terminals) on the front panel to the rear panel. Moreover, it abandoned the remote control function. It was said that customers in Japan and Europe preferred to have them without remote control function in order to reserve an everlasting and classical sense.

Simultaneously, that is in February 2004, Audio Space had started exporting the AS-300B's MKII SE version to Japan. With adoption of a larger power supply and output transformer, it increases the power output from 8W to 10W while it also enables end-users to adopt more powerful but also more demanding tubes like EAT, KR, VV, Emission Labs, etc. These especially powerful 300B tubes include 300BX and Full Music 300B/n/+ (amplifier has to be modified) but 30B, 32B and 52B?are excluded. Another improvement is the auto balancing of the hum sound where manual adjustment is no longer required. The sound source input terminals are increased from 2 to 3, plus a pair of direct RCA input terminals (signal will not pass through the selector and volume control) for the usage as pure power amplifier. It has only a pair of RCA output jack as well as the headphone jack. It is only after the mid of 2004 that such MKII SE version was released in the local Hong Kong audio market.
AS-6i (300B)

The Duntonic DU-6i (300B) which we saw in the advertisement and manufacturer's catalogue before has now been changed to Audio Space AS-6i (300B).

At the end of 2002, Audio Space developed a brand with the name of Duntonic in its own plant. The early models included: DU-6i (KT88), DU-3i (EL34), DU-2i (EL84) and DU-2.8i (6V6). Based on the figuration, function and equipment of DU-6i as well as the 300B tube, AS-6i began its trial sale with the name of Audio Space in Japan in December of 2003. It was until April of 2004 was the same model of Duntonic DU-6i (300B) available for sale in Hong Kong. Audio Space was the exporting version which aimed at exporting to Japan, Singapore and Europe. On the contrary, Duntonic was a version for sale in domestic market. . After 80 panels of Duntonic DU-6i (300B) were used up, Audio Space didn't manufacture additional panels. Moreover, it adopted the mark of ?Audio Space? to AS-6i (300B) and introduced them to the market. Any owner of the Duntonic-marked amplifier would have become one of the collectors of these 80 sets limited version amplifiers.

As same as AS-300BMKII SE, AS-6i also adopts the tube of 6SL7×2+6SN7×2. Its powerful amplifying tube adopts two 300B for each track, which is the same as MP-1B. The two 300B operates via split convert phase circuitry to provide output up to 21W. Audio Space Lau told me that this machine actually is capable of providing RMS power output up to 28W, and the 21W was only a conservative figure. In addition, he also told me that its low frequency could be increased to 10Hz-1dB with adoption of technology developed by Reference 1. In view of manufacturing workmanship of 300B, the submerging capability of its low frequency is really astonishing.

As same as AS-300BMKII SE, it has three pairs of RCA input options plus a pair of direct, RCA output as well as a safety cover.

The following is the comparison table of three models of 300B amplifiers.


Small tubes

300B power tubes

Power output

Power Transformer

Output Transformer

Current Consumption Loop


Speaker impedance



6SL7 X 2

6SN7 X 2


10W X 2

Class A


80W X 2


Dual use as

Integrated/Power Amp



12AX7 X 2

6SN7 X 2


21W X 2

Class A


80W X 2


Dual use as Integrated/Power Amp


(per pair)

6SN7 X 2

12AU7 X 2


18W X 2

Class AB

108W X 2

50W X 2


Pure Power Amp



As I have formerly issued comments on MP-1B for two times (respectively in Vol. 191 and 205), therefore the introduction to sound comparison herein is relatively brief. Also, I will spare a few comments for AS-300B MKII SE and AS-6i (300B) on which I have never issued any comments.

Since its post-model was developed in 2002, MP-1B has remained unchanged, and only went through two obvious modifications. Firstly, it introduced the output transformer manufactured with new procedures. Secondly, the previous long-tail inversion phase circuitry was replaced by split inversion phase circuitry for driving operation, which was widely regarded as more advanced in the process of developing integrated Duntonic amplifier.

This power amplifier has two groups of RCA input terminals. Input 1 adopts the so-called high gain which is free of attenuation. In order to accommodate the front high frequency output, Input 2 adopts low gain with attenuation. In the process of AB test, I selected the high gain which was capable of producing powerful, penetrative sound effect and high analyzing performance.
Part 1: Operation as integrated amplifier

I divided the game into two stages. The first stage was to test the performance of the equipment used for amplifier assembly. Among them, there were AS-300B MKII, AS-6i but MP-1B and AS-8iMKII which adopt the powerful amplifying tube such as KT88 but AS-8iMKII.

During the AB test, I turned down the selection knob for negative feedback of 3 machines to the minimum. In this way, AS-8i was capable of producing transparent sound with the combined operation three machines.

After comparison, I made a conclusion. Which difference was bigger? Was the difference between AS-6i with 300B for driving operation and As-8iMKII with KT88 for dynatron driving operation or AS-300B MKII SE with 300B for single end operation? After comparison of different records, I felt that AS-300B MK II had its own characteristics, and its romantic nature was so obvious and unique. On the contrary, the sound produced by the two models used for driving operation was almost the same regardless of the different big and small tubes and different driving circuitries (split inversion phase for As-6i, and Long-tail inversion phase for As-6i) adopted by them. At least their performance fell far behind the AS-300BMKII SE.

Among the 3 models, the sound of AS-300BMKIIwas the sweetest and mildest. However, its penetrative power and brightness was inferior to the other two models. That mean its appeal was not high enough. It's the common phenomenon occurs on amplifiers of 300B which are famous for their colorful and variant sound. Audio Space Peter Lau told me that he intentionally created this kind of sound, because most of audiophiles liked it. According to their opinion, it was most probably impossible to expect sweet sound when the penetrative power was too strong. Furthermore, he added, if the buyer liked more penetrative and smooth sound, he only needed to make slight modification to the circuitry.

While playing 《Beethoven Triple Concerto》CD, AS-300BMKII SE effectively recovered the mild, easy and smooth sound characteristics of violin and cello. At the same time, the unique style, sound quality as well as the smooth flow and springy rhythm of instruments were brought into full display. The piano manifested its excellent power at its high performance. Even though each channel had only one 300B, the fidelity and the submerging power at low frequency was very good (of course, it was still inferior to the advanced Audio Note Quest Silver and Dignity 300B of the standard version both of which cost above HK$50,000, which I have tried before) with a touch of tenderness and easiness. By the way, the focusing power for the 0 negative feedback adjustment of the first edition of AS-300B was average, which was not up to my requirement. Therefore I usually use ? 3dB negative feedback. However, the MKII SE's MIN (actually it is 0 negative feedback) was capable of controlling the low frequency of N803 to the extent that is acceptable. On the contrary, the sound produced by MAX (-3dB) had a sense of tightness and limitation, which lacked of dynamic characteristic and atmosphere. In terms of its differential ability, separation and control power at the tutti, this type of amplifier was inferior to both AS-6i and AS-8i MKIII.

While playing "If Love is forever", the 13th song in Hugo's 《Autumn Moon》, the singing by Huang Hong-ying sounded romantic and tender with the high performance of AS-300BMK II.

Audition was conducted in the testing room inside our office, and relevant equipments are as follows:

Acoustic Arts Drive 1 CD Player
MSB Platinum Link Plus Decoder
Audio Space Line 1.1 Pre-amplifier
AS300BMKII Amplifier
AS-6i (300B) Amplifier
MP-1B Amplifier
AS-8i MKII Amplifier
B&W N803 Loudspeaker
Synergistic research designers' reference X Digital line
Audio Note Sogon Signal wire
Silver Ribbon S-182 Signal wire ( front and rear)
Harmonix HS-101 Loudspeaker line
Isoclean Auto Focus power line ( Amplifier)

This is the representative unique skill of 300B while working in Class A single-end mode. When I used the AS-6i (300B) widely used as integrated amplifier to play the record mentioned above, I found the sound effect is much different.

When I turned on the volume, immediately, I could feel a more brilliant timbre and a brighter sound effect coming out from AS-6i. Audio Space Peter Lau told me the sound effect would be brighter and more flowing after slight modification. The current performance was sufficient to meet the demand in the market.

Once again, I used AS-6i to play 《Beethoven Triple Concerto》. The sound of violin produced by it was bright, fleeting and powerful. At the climax, the performance of violin could be described as overwhelming. On the other hand, its performance at low frequency was vigorous, fleeting and with high differential ability. As an amplifier of integrated model which cost no more than one hundred thousand Hong Kong dollars, the deep, vivid and vigorous sound of violin, magnificent and dynamic spectacle of brand as well as the hierarchy of instrument was invulnerable. At least, they were better than AS-300B MKII SE.

Similarly, I once again used it to play the 13th song of 《Autumn Moon》. The sound of piano sounded more transparent, more solid and springy which thoroughly manifested the deserved characteristic of piano. The singing by Huang Hong-ying was straight and honest, bright and vigorous, yet with smooth and mellow timbre normally produced by 300B. Though the sound was not as tender and smooth as that produced by AS-300B MKII, it was moving enough in my eyes.

While playing the passionate episode of "The Death of Liang", Zhu Throws Herself Into The Grave? in Hugo's《The Butterfly Lovers - The Yellow River》xrcd2, As-6i thoroughly brought into display the sentimental and tragic atmosphere. At the same time, the smooth and flowing hierarchy created by 300B added to the tragic atmosphere a touch of lingering plaintive sense.

After that, I connected the integrated amplifier to the most economical AS-8iMKIII. This amplifier was very much the same as AS-6i in terms of its brilliance, speed, control power, focus and differential performance. However it was easy to find the difference between the two while in terms of small tube performance, especially, in terms of the display and sensation.

I changed amplifier every time after I tied small segment of music. As a result of it, I found the AS-6i exceeded the AS-8iMKII in terms of its abundant and full sound, flush and lingering flowing nature and smooth yet flexible hierarchy. Through comparison, I found that AS-8iMKII had a simple and original hardness in terms the flowing of sound, whereas, the AS-6i maintained the smooth, flowing and tender sense at the interchange between rapidness and slowness. Though the difference between the two was not obvious at all, it appeared to me that As-6i was capable of giving you a charming and lingering with repeated listening. It's the feeling you can experience only on condition that you are highly concentrate while listening.
Part II: Operation as power amplifier

After testing the few sets of integrated amplifier, I would use the Audio Space Line-1.1 pre-amplifier to match with AS-6i and AS-300B MKII SE to test their performance again being a pure power amplifier (direct input). Meanwhile, I?ll also include MP-1B in this game to make a comparison among these 3 models of power amplifier. Since AS-8i does not have direct input, it was excluded from this game.

At first, I used AS-300BMKII SE to play the 3rd chapter of Ma Siu Sin?s 《Secret of Love》 which bears the same name as the album. When the sound came out, I felt an abundant, mellow, stable timbre I have never experienced in the Part-One testing. The sound of guitar, vocal and string sound was condense and easy. Driven by this power, the sound produced by the loudspeaker was easy, stable and measured. When playing the 4th song "Black Bamboo Trio", the singing of Ma Siu Sin sounded extraordinarily romantic and charming as driven by the AS 300BMKII SE. The variant melody of Wong Mui opera sounded very smooth and graceful.

Driven by the pre-amplifier, the sound quality of the music center was more powerful. Therefore, I used the AS 300BMKII SE to play the passionate jazz music , i.e. the 9th episode of 「Solar」in 《Original Jazz Music》, the segment. When the sound came out, I could feel the sound performance of saxophone on the left and right, niujin and piano was excellent. Though the focus and differential power was not strong enough, and the speed was far from fast, it revealed a sense of stability. It thoroughly displayed the nature of jazz music, and it was much better than those models without front amplifier.

When playing 《Beethoven Triple Concerto》, the overall sound display of grand brand tutti was much better than previous performance. Meanwhile, the integrity of the band was maintained, even though the offbeat and the speed variance were not extraordinary well. However, the easy romantic characteristic of the AS-300BMKII was reserved.

After that, I used the AS-6i (300B) to play the 3rd and 4th song of slow rhythm in the 《Secret of Love》. Though it could not be said that the speed and power of AS-6i far exceeded the AS-300BMKII SE, the difference between was not so obvious. While playing the Wong Mui opera, aesthetic feeling and attraction manifested by As-6i was not as excellent as that of produced by AS-300BMKII SE, which lacked the aesthetic feeling of tenderness and smoothly dynamic characteristic.

In succession, I used it to play the ninth driving music in 《Original Jazz Music 2》. AS-6i had the overwhelming advantage in displaying the high speed frequency shift in playing the 3rd orchestral music in 《Beethoven Triple Concerto》and the violin concerto in 《The Butterfly Lovers‧The Yellow River》. The sound effect produced was very extensive, and the separation and control power as well as speed and dynamic characteristic was as much the same as the that of AS-300BMKII SE. Moreover, its upper and lower extension was even better than AS-300BMKII SE. As a matter of fact, according to the specification of user guide, the frequency response (10HZ-20HZ-0.5db) of AS-300BMKII SE at the low frequency was better than that (20HZ-30HZ±1db) of AS-6i. According to Audio Space Peter Lau?s reply, the frequency response of amplifiers with different power output was measured in terms of the different requirements. AS-6i was supposed to drive loudspeakers that were difficult to drive. Therefore, when two amplifiers were respectively used to drive N803 in playing records with high dynamic and magnificent sound effect, AS-300BMKII SE displayed the low submerging power at low frequency due to insufficient power yet the more accelerated frequency shift at low frequency setting.

Driven by Line 1.1, the balance, power, speed as well as differential ability and magnificent sound effect of AS-6i were brought into full display, which far exceeded the AS-300BMKII SE with each track equipped with one 300B. I even felt that the sound effect created by AS-6i was much better than that produced by Line 1.1. However, its speed and differential ability at low frequency has not yet been at their high performance. The only advantage of AS-300B MKII SE lies in the romantic feeling produced in playing the tender melody with slow rhythm.

The last one I tested was MP-1B. This power amplifier was very different from the other two mentioned above in terms of its sound effect. Firstly, the compact and graceful sound produced by it teemed with clear hierarchy and vivid figuration, which was different from the abundant sound effect produced by the other two amplifiers. Secondly, its timbre was pure and pleasing with a touch of noble nature which made the brilliant sound produced by the other two amplifiers look pedestrian and ordinary. Furthermore, it also had other characteristics such as accelerated rhythm, high analytical ability and excellent upper and lower extension which were free of any encumbrance. Although its sound at low frequency was not as abundant as that of the other two amplifiers, its submerging ability and springiness was much better, which had a touch of civilized aesthetic feeling at frequency.
Prejudice and examination on authentic as well as imperfect circuitry
Three amplifiers of the same brand with three different designs produced three different kinds of sound effects. The interesting thing was that the amplifier which was less attractive to me was the single-end triode Class A amplifier, which is however regarded by most audiophiles as the most authentic and classic one. On the other hand, it was the Class AB push-pull amplifier that was capable of producing a timbre with elegancy and free of trivial defects. What does such phenomenon prove? In my opinion, there are at least three points. Firstly, the theory is fixed, whereas the application is flexible. Any circuitry that can produce excellent sound effect was a good one. Secondly, the excellent sound effect is in proportion with the price of the amplifier. The most expensive MP-1B is characterized by its excellent sound effect and figuration rather than its power. Thirdly, audiophiles like me who favors 300B judge a certain amplifier in terms of sound effect rather than whether it is of single-end triode or not. I have never found any coarseness produced by push-pull design due to distortion. What about you?
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