In the weeks following my review of the superlative-sounding Melody AN 300B integrated amplifier
, I received numerous inquiries from readers who had the type of high-sensitivity and stable nominal-ohms-rating speakers that synergize with a push/pull 300B amp. Since they already owned a line stage, they were looking for what I could recommend in either a single-chassis amp or pair of mono-block 300B amps. I started to research companies that manufacture well-regarded 300B-based amplifiers based on build quality, sonic performance and a price around $4,000. This led me to a Hong Kong-based company called Audio Space Acoustic Laboratory Ltd.
, which has been in existence for over 20 years. I contacted Thomas Poon of GINI Systems, which is the U.S. importer for Audio Space, to discuss which 300B amp I could review. With a price of $3,490, the AS-6M (300B) push/pull mono-block amplifier became the best candidate for this review. This amp has a special feature: each mono block has a volume control, allowing for a line stage to be added later for even higher performance.Additional Resources
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The AS-6M mono block has a handsome appearance, being a silver chrome chassis with black-lacquered transformer and tube cages. Each AS-6M weighs 34 pounds. The dimensions of each chassis are 7.5 inches high, seven inches wide, and 18.5 inches deep. On the top of the chassis, toward the back, sit the hand-wound power supply and output transformers. A pair of 300B tubes sits adjacent to the transformers, and at the very front are the driver tubes, one 6SN7 and 6SL7. Located behind the AS-6M mono blocks is the IEC power inlet. Next to the IEC inlet is either a pair of single-ended inputs for driving the mono block direct from your line stage or two pairs of single-ended inputs for your source components, if you use the AS-6Ms as a pair of integrated amps. Each AS-6M produces 21 Triode Class-A watts and provides two sets of very high-quality four-ohm or eight-ohm speaker posts.
Located on the front panel are two chrome knobs and two toggle switches. One of the knobs is the on/off switch; the other knob is the volume control, if you use the amp as an integrated amp. The first toggle switch gives you the option of driving the amp directly by a line stage or using it as an integrated amp. The second toggle switch controls the amount of negative feedback from zero to three decibels. Regardless of what line stage or speakers I used to review the AS-6M mono blocks, I always preferred the negative zero feedback setting. I found that adding the three dB of negative feedback dried out the wonderful timbres that these mono blocks have to offer, along with shortening the depth of the soundstage.
Joao Paulo's Almas (M-A Recording, Saint George British Anglican Church, Lisbon, Portugal) can demonstrate an amplifier's ability to produce a large acoustic space with natural decays. The music is played on a Steinway concert grand piano, along with soprano sax and acoustic bass. When I played the song "Aldeira," the AS-6M mono blocks created a deep and wide soundstage, giving me the illusion that I was sitting in Saint George in Portugal listening to this beautiful acoustic jazz. The level of transparency/clarity was very high, which allowed all the echoes bouncing from the church walls to be clearly heard.
My next selection was "In a Sentimental Mood" from guitar player Warren Battiste's album Quiet Storm in New Orleans (Progressive). I chose this to see how the AS-6M amps would handle tone and timbres. The strength of a reference-level 300B-based amp is its grainless rendering of the timbres of different instruments. If the 300B amp is producing its magic, it should be easy to hear the tonal differences between a Gibson and Fender electric guitar, regardless of how the individual player tunes it. During "In a Sentimental Mood," the hollow-bodied Gibson just floated into my listening room with beautiful and realistic timbres, along with precise imaging and density. Another aspect of this selection is that the top end is extremely well-recorded, with great extension and tons of air surrounding the drummer's cymbals. The AS-6M mono blocks were able to deliver all this information in a natural way.
To test whether the AS-6M mono blocks could deliver overall macro-dynamics and low-end extension, I chose "Inside-Out" from bass player Damian Erskine's album To Speak (De-2 Records), which contains very dynamic bass and electric piano. Regardless of whether I used the Lawrence Audio Mandolins, Vapor Audio Stiff Breezes, or Birch Acoustics Ravens, the AS-6M mono blocks delivered the pop/dynamics and kick of Damian Erskine's album with no attenuation of the lower frequencies.
Read about the high points and low points of the AS-6M mono blocks on Page 2.