For over a year-and-a-half, I have been on an odyssey, listening to different tube-based amplifiers. I have heard some of the highest-regarded parallel, push/pull, and single-ended designs based on 211, 300B, and 845 power tubes on the market today. During this experience, I realized that I was finding it more and more difficult to go back to my reference solid state amplifiers. Even though these amplifiers are terrific and rank with some of the best solid state designs in their own right, they could not match two key sonic traits of very high-end tube designs. First, the density of tone, timbres, and color can sound ever so slightly washed-out. For example, a brass instrument would not have that gorgeous "brassy" sound you'd hear in a live setting. Secondly, individual players lack what I refer to as image density, palpability, or a sense of air around each instrument on the soundstage. Tubes do have their allure, but they also have their well-stated drawbacks, including maintenance, heat, warm-up and so on.
Determined and motivated, I began to search for a pure Class A solid state amplifier that might address these shortcomings and still provide what great solid-state Class A amplifiers have to offer: transparency/details, a grainless liquidity, and dynamic impact. The highly regarded, 30-year-old, Britain-based company Musical Fidelity had in its reference-level line an amplifier called the AMS50, which retails for $13,999. It is based on a pure Class A design. Unlike many solid state amplifiers that produce pure class A in their first few watts and then cross over into a Class A/B bias, the AMS50 stays in pure Class A. The AMS50 has 50 watts into eight ohms and 100 watts into four ohms throughout its total power rating. Don't let the power rating of 100 watts into four ohms fool you into thinking that the AMS50 would not do well at driving low-efficiency speakers. Its peak-to-peak current rating is a whopping 100 amps. The AMS50 has enough current to drive virtually any speaker on today's market with control and ease. The amp is based on twin high-current amplifier sections in a bridged configuration with a tremendously stiff power supply.
The AMS50 is a beautiful-looking amplifier that comes in matte gray finish with a black centerpiece. The front plate has a power switch button in the middle and two sets of discrete LEDs showing power/standby, operating status, and temperature status. Behind are two pairs of dual speaker binding posts, two pairs of either XLR or RCA inputs, a selection switch for the inputs, an on/off power switch and, finally, the IEC socket.
During its stay in my reference system, the AMS50 powered four different sets of speakers, including the Lawrence Audio Cello and Mandolin, the Birch Acoustic Raven, and the Vapor Audio Stiff Breeze. Additionally, it was driven by three different preamps (Concert Fidelity CF-080, Raven Audio Shadow, and Burson Soloist) and three different digital front ends (Concert Fidelity DAC-040, Woo Audio WDS-1, and Grace Design M902. The AMS50 was so transparent, with no apparent noise floor, that any changes in upstream gear could easily be heard by both the trained and untrained ear. I would not recommend leaving it on all the time, due to an increase in your electrical bill. Class A amps basically have two modes of operation: all-on or completely off. That's the beauty of the design and Energy Star ratings be damned, because this kind of amp just drinks power from the wall. It's the nature of the beast. The good news is that this amp warms up to optimal performance pretty fast - 10, maybe 15 minutes, it's ready to rock.
Once I had set up the Musical Fidelity AMS50, what was intended as a short listening experience became a three-hour auditioning period with my reference system, which was composed of the Lawrence Audio Cello speakers, the Concert Fidelity CF-080 preamplifier, and the Concert Fidelity DAC-040. I was in awe and total disbelief as I found myself unwilling to walk away from my listening spot. The Musical Fidelity amp had the magnificent virtues of a pure Class A amp in its purity of tone and overall grainless liquidity, with no sense of solid state artifacts, such as etch or dryness. What distinctly separated it from my solid state mono-blocks and any other solid state amplifier was in three significant sonic attributes.
When I played the entire album Noir (Anzic Records) by Anat Cohen and The Anizic Orchestra, what was very apparent on Ms. Cohen's tenor/alto/soprano/clarinet solos and the backing of the brass section was the voluptuous tone color that I had only experienced with great tube-based amplifiers. The density of the timbres was beautiful and effortlessly rendered.
One of my favorite alto saxophone players is the great Frank Morgan. I had the pleasure of hearing him live on two wonderful occasions in Chicago. The track "Round Midnight" from his album City Nights (HighNotes) showed another striking aspect of the AMS50's performance. From octave to octave, Frank Morgan's alto saxophone playing interwove effortlessly with his excellent trio of jazz stalwarts, yet still gave each player an image of three-dimensionality. The ability to render this type of individual image density/palpability would be closer to what tube lovers are seeking in their systems. Additionally, because of its very low noise floor, the AMS50 allowed micro-details to be easily heard, along with accurate depth and width in its production of the soundstage in the recording.
When I played the legendary album Blue Train (Blue Note Records) by John Coltrane, the AMS50 was able to produce the nuances of his very unique tonality/timbres on his tenor saxophone with great precision. This album was recorded in a small studio setting, with the horn players spaced around one microphone. The AMS50's spatial presentation was so accurate that it was easy to hear each player's position as each walked up to the microphone to take his solo.
Musical Fidelity's AMS50 amplifier is the best-sounding solid state amplifier I have ever heard in my system. It comes the closest to negating the dichotomy between what tubes have to offer - richness in color/tone, warmth, image density/palpability - and what solid state designs have to offer - speed, transparency, accurate leading edges, resolution and low-end control/power. However, there are some concerns if you want the AMS50 to be the heart of your two-channel audio or home theater system. This amplifier is a very handsome-looking beast, but it is quite hefty and large. It will take up a vast amount of floor space and needs to have plenty of clearance for ventilation so that it does not overheat.
Taking into consideration that it runs extremely hot, it will warm up a fairly large-sized room rather quickly. As mentioned before, Class-A power amps also drink AC power like there is no end to the supply, so you could realistically notice an uptick in your power bill if you leave them on all of the time. They also could heat your listening room if you live in a cold-weather climate.
Comparison and Competition
Two solid-state amplifiers in the price range of the AMS 50 that would be true competitors are the Pass Labs XA-60.5 mono-blocks, which retail for $11,000, and the Ayre Acoustics MX-R mono-blocks, which retail for $18,500. Although the XA-60.5 is comparable to the Musical Fidelity amplifier, the AMS50 clearly surpasses the XA-60.5 with its musical tone, color, timbres, image density/palpability and ultimate dynamic impact.
The Ayre Acoustics MX-R mono-blocks, when compared to the AMS50, offered a drier tonality and lacked the liquidity of the AMS50. The Ayre Acoustics MX-R mono-blocks also produced a soundstage that was much less three-dimensional and shorter in its depth then the AMS50.
Musical Fidelity's AMS50 amplifier surpassed what I thought a solid-state amplifier could provide in its ability to offer warm, natural timbres, density of color, holographic imaging, and a flowing seamlessness across the frequency spectrum. It has all the sonic virtues of pure Class A amplification, blending what a great 300B/211/845 tube-based amplifier brings to the music with the transparency/details and power of solid-state. However, due to its hefty build and need for ample floor and ventilation space, its massive heatsinking, and the large amount of heat it produces, the output devices never shut off. Putting aside its physical drawbacks, the Musical Fidelity AMS50 will most definitely evoke a mirage of live music being played in your room. My own Pass Labs XA-60.5 mono-blocks are some of the most highly-regarded solid state amplifiers on the market today. Musical Fidelity, with the AMS50 Amplifier, has entered into this realm of reference-level performance. I highly recommend that you put this amplifier on your audition list if you are looking for an ultimate-level solid state (or tube) power amp.