Musical Fidelity M6 PRX Power Amplifier Reviewed

Musical_Fidelity_M6_PRX_amplifier_review_silver.gifI was pretty enthused to receive a call from Musical Fidelity‘s U.S. Distributor Tempo Sales. When I was asked if I would be interested in reviewing the preamplifier and amplifier from Musical Fidelity’s M6 series I jumped at the chance to spend time with one of the newest products from this venerable manufacturer. For those of you not familiar with the Musical Fidelity lineup, the M6 series sits just above the midpoint of the lineup and is comprised of two integrated amplifiers, a CD player, preamplifier and the amplifier discussed below.

Additional Resources
• Read more amplifier reviews by the writers at Home Theater Review.
• Find a pair of floorstanding speakers for the M6 PRX to drive.
• Explore AV receiver reviews in our AV Receiver Review section.

Musical Fidelity has been on my radar for well over a decade with their innovative products. Their high end Nu-Vista series utilized unique, metal-enclosed tubes called NuVistors to great critical acclaim. The original X-Can series of components were housed in finned, aluminum cylinders and were reported to offer great bang for the buck. The cylindrical housings reduced manufacturing costs while providing a relatively resonance-free chassis. The unique form factor made for an interesting aesthetic statement, especially when one had multiple X-Can components in the system.

The M6 Series is designed by the Musical Fidelity team in the United Kingdom but is manufactured in Taiwan to keep costs down. Even though the M6 PRX is made halfway across the world from Musical Fidelity’s headquarters, the design is pure Musical Fidelity. The M6 series of products are not inexpensive but they are designed to be a relative bargain. At $3,500 the PRX amplifier offers the buyer significant bang for the buck when compared to the competition.

The M6 PRX circuit topology shares many design elements with the Musical Fidelity’s more expensive Titan and AMS amplifiers. One design element unique to Musical Fidelity’s solid-state amplifiers is the dual bi-filar Choke Regulated Power Supply (“CRPS”). While chokes have been used in many tube amplifiers, Musical Fidelity is the only company I am aware of to use them in a solid state amplifier. Musical Fidelity has been utilizing choke regulation in solid-state amplifiers for over 20 years. The CRPS system is designed to passively reduced power supply noise. The choke offers high resistance to AC and low resistance to DC, which, when properly implemented, results in a smoother power supply wave form. John Quick explains that the bi-filar windings keep the B+ and B- within the same choke to offset each other’s noise and magnetic field, which also leads to better noise rejection. Musical Fidelity identifies the power supply as the heart of the amplifier and takes these unique steps to maximize the performance of the power supply.

The amplifier is a fully balanced, dual mono, class AB design with four pairs of output transistor devices per channel (This is one more pair of devices per channel than 200 Watt per channel M6i integrated.) and is rated at 260 Watts per channel and signal to noise ratio of greater than 120dB “A” weighted. The high current design is said to deliver constant voltage even with hard to drive speakers. The chassis of the M6 PRX bears a strong resemblance to the other pieces in the M6 series and indeed to other Musical Fidelity products and can be had in either silver or black finishes. My review sample had been a demo unit for a while and despite some signs of wear, demonstrated itself to be a well-finished product. The aluminum front faceplate has pronounced horizontal bevels along the top and bottom edges, a design touch one will note in the AMS, M3 and M1 series as well. The 43 and a half pound amplifier is housed in a relatively compact package measuring 17 and a third inches wide by five inches high and 15 and a half inches deep. The faceplate has a ‘medical grade stainless steel’ badge with the model name just below the upper bevel on the left side. Other than the badge, the faceplate is symmetrical with silver ovals just flanking the centerline just above the lower bevel. The ovals contain led status lights and are flanked by a power button on the left and an input selector on the right. One can use the input selection to choose between the “A” and “B” inputs. This will make it even easier to integrate the PRX into a home theater system when your preamplifier does not have a home theater pass through. Horizontal heat sinks run down each side to the rear panel and were nicely finished with rounded edges that were friendly to my fingers when moving the unit. The rear panel is fairly complete with two sets of single-ended inputs, a set of balanced inputs, a single-ended output for pass through to another amplifier or powered subwoofer, two pairs of binding posts and an IEC power connector. Notably missing was a 12-volt trigger input.

The Hookup
I set the M6 PRX up in my reference two channel system. The primary source was McIntosh’s MCD-500 CD/SACD player feeding into a McIntosh C-500 preamplifier. Other sources included Cary’s 303T CD/SACD/DAC and the PS Audio Perfect Wave DAC. McIntosh C-500 tube preamplifier was utilized for all critical listening. I also used the companion preamplifier from Musical Fidelity, the M6 PRE, but for critical listening I wanted the only new component in the system to be the amplifier being reviewed. Transparent‘s new MM2 Ultra interconnects and speaker cables were also used. Finally, the speakers I listened to included both MartinLogan Summits and Acoustic Zen Adagios.

Connections were fairly straightforward. I used balanced interconnects from the preamplifier and my speaker cables had spade type connectors. I also hooked up single-ended interconnects from the PS Audio DAC and McIntosh MCD-500, both of which have variable volume outputs. This was not used for critical listening but let me evaluate the amplifier’s ability to integrate into two systems simultaneously.

The physical layout of the connections could make hooking up thick, audiophile cables difficult. The binding posts accept spades or bare wires; perhaps the plugs in the binding posts could be removed to accommodate binding posts, but I didn’t attempt to do this. With spades I find I normally have to have the wires come in from the sides if they are not flexible enough to bend before hitting the shelf below. If one utilizes the inner set of binding posts with thick, stiff speaker cables that are prevalent in the audiophile world they will likely make routing and connecting the interconnects a bit of a challenge.

The review sample I received had been used as a demonstration unit and had been broken in. Nonetheless, I let the amplifier play for a few days after hooking it up just to make sure.

One of the first pieces of music that caught my attention as I was working in the room in which the stereo was playing was Livingston Taylor’s “Isn’t She Lovely” from the album Ink (Chesky CD). When I heard Taylor’s whistle on this acoustic cover of this classic it sounded so natural and real I instinctively looked up from my book to see if someone else walked in and was whistling with the song. The voice was completely natural and was situated slightly behind the plane of my speakers. The soundstage was simple but persuasive with a natural, relaxed presentation. Tonal balance was neutral throughout the octaves. Notable was the absence of noise; the noise floor is extremely low on this amplifier, which is noticeable on well-recorded albums such as this one. Unfortunately, I did not have access to the 96 kHz – 24 bit version for comparison; it would have been interesting to listen for detail between the two versions.

Read more about the performance of the M6 PRX amplifier on Page 2.

Musical_Fidelity_M6_PRX_amplifier_review_black.gifThe next album I listened to was Rush’s Moving Pictures (Mercury
Records), which I downloaded from HD Tracks and is a 96kHz/24 bit FLAC
audio file. Playback was via PS Audio’s PerfectWave DAC’s network
bridge, review forthcoming. I was unable to use the DAC in the Cary
303T as I have not yet replaced the Sonicweld USB to SPDIF converter
that I had to send back to the manufacturer. I have long been a fan of
Alex Lifeson’s guitar work and was looking forward to listening to this
high resolution version of an old favorite. I was immediately greeted
by familiar sounds, everything sounded as it should, the vocals and
instruments were as they should be, the soundstage was deep and better
defined than on the CD version.

However, I was missing some of the
immediacy I have come to expect from Chesky’s higher resolution audio
files. I tried playing the same tracks through my McIntosh MC501
amplifiers (which at $11,000 a pair are over three times the price of
the Musical Fidelity amplifier) and found a greater sense of immediacy
to be the most notable difference between the two amplifiers. The
immediacy was particularly noticeable with Lifeson’s electric guitar.

Wanting to stick with some high-energy rock I played Godsmack’s
“Battalla de los Tambores” from their Changes DVD (Coming Home
Studios). I played this track through both the MartinLogan and Acoustic
Zen speakers. This track features dueling drums, which gave the Musical
Fidelity ample opportunity to show off its macro dynamic capabilities.
At any sane listening level, and even a bit beyond, the amplifier never
strained. There were no signs of compression or loss of control. The
drums remained tight and tuneful with well-defined notes and decay.
When I listened to this track I was already more than an hour into that
day’s listening session and the amplifier was very warm afterwards. It
was not too hot to touch but I would be sure to place it in a
well-ventilated space.

Lastly, I played a piece that tests both macro and micro dynamics
and that has been in heavy rotation at my house: Carl Orff’s Carmina
Burana (Telarc SACD). The tracks Fortuna Imperatix Mundi “O Fortuna”
and “Fortune plango vulnera” are complex pieces that test both sheer
dynamics and detail of a system. The soundstage was appropriately
immense through the M6 PEX. When compared to the NuForce Ref9 V3 SE
($5,000 per pair), the Musical Fidelity had more weight and a larger
soundstage. Bass control was close between the units with a slight nod
to the Musical Fidelity and the NuForce edged ahead in the area of

Competition and Comparison
The NuForce Ref 9 V3 Special Edition
and the Cambridge Audio Azur 840
come to mind as potential options. I have not heard the Cambridge
amplifier but the NuForce amplifier retrieves slightly more detail but
also comes with a price premium of approximately 50 percent. For more
on amplifiers in general, visit Home Theater Review’s Amplifier page.

The Downside
The M6 PRX is missing two features I would like to see on an amplifier:
a 12-volt trigger and good binding posts. The trigger allows for easier
integration into a system by automating turning the amplifier on and
off. This is especially helpful when the unit is packed away in a hard
to access cabinet. The binding posts did not facilitate all types of
speaker cables and their build quality did match that of the rest of
the amplifier.

It was hard to find fault with the amplifier’s sonic performance. It
is not the last word in detail or power but within the boundaries of
what it does, it does them extremely well. The amplifier has an
extremely low noise floor, which would normally mean an exceptional
amount of detail would be discernible due to the absence of noise.
While the M6 PRX exercised great control over the musical notes,
without a sign of bloat or muddiness, this control is also the
amplifier’s greatest sonic pitfall, although this is a matter of
personal taste. Audio components must walk a fine line with damping;
too little and the music will be ill defined, too much and some of the
nuances will be lost. For my taste, the M6 PRX, is slightly on the too
much side of the damping. To the amplifier’s credit I would rather have
the music clean, controlled and slightly over-damped rather than the

The Musical Fidelity M6 lineup, and in particular the M6 PRX reviewed
here sits in a critical spot in the audiophile world. At $3,500 it is
not an inexpensive piece where second-rate sonic performances are
tolerated, nor is it a pinnacle product expected to have world class
build quality and sonic performance. Placing a product in this position
requires some tough choices and I think Musical Fidelity made some good
decisions with the M6 PRX. While the amplifier is attractive and
reasonably well made, one will not confuse this with a Jeff Rowland component or even
one from Musical Fidelity’s similarly styled higher end products. Money
is not wasted on superlative build quality; rather the money is spent
on the components that comprise the amplifier and achieving a certain
level of sonic performance. This is consistent with the decision to
have the amplifier designed by the acclaimed designers in Britain and
then built in Taiwan. If you treat your products with normal care and
do not require eye candy, this should not pose any problems.

If you are looking to spend $5,000 or less on an amplifier the M6
PRX is very much worth taking a listen to. One would never confuse the
sound of this amplifier with one of a tube amplifier but it does have
some similar sonic qualities that I enjoyed. The M6 PRX had a grain
free easy presentation that made long listening sessions enjoyable. It
also had some of the better qualities of s solid-state amplifier such
as a low noise floor, good bass control and impressive dynamics.

Additional Resources
• Read more amplifier reviews by the writers at Home Theater Review.
• Find a pair of floorstanding speakers for the M6 PRX to drive.
• Explore AV receiver reviews in our AV Receiver Review section.