Musical Fidelity M6x Vinyl Phono Stage Reviewed

Last year I reviewed and subsequently purchased the Musical Fidelity M6 Vinyl phono stage. A highly configurable three-input phono preamplifier, the M6 Vinyl has since provided me with exceptional performance with a low noise floor and neutral sound. It has proven an ideal companion for auditioning cartridges, turntables and of course, vinyl. Though it left me wanting nothingwhen its successor was announced I immediately asked for a sample.

Despite the stellar performance of the outgoing model, the claims bestowed upon the M6x Vinyl in the available literature are bold. Most notably the suggestion that the M6x Vinyl will “deliver the ultimate performance possible from any phono source”. To me, “ultimate” performance implies superlative technical design and engineering resulting in a preamplifier that is sonically neutral, has no practical loading or driving limitations and, in the case of a turntable preamplifier, tight adherence to the RIAA standard.

The outgoing M6 Vinyl (hereafter the M6) met these requirements, and so I unpacked the M6x Vinyl (hereafter the M6x) with great interest.

The unpacking process hasn’t changed. Double-boxed and nestled amid thick foam blocks, the M6x is wrapped in a velvet drawstring bag. A spiral-bound manual, cotton gloves and an IEC cable round out the box contents.

Externally the casework mostly resembles the M6, though with a vastly improved front panel finish. It’s smooth to the touch and a far better finish than before with the same groups of buttons and lights spread along the fascia. Those buttons switch power, loading, RIAA standard, gain, cartridge type and input; all indicated by respective LEDs and neat lettering, though with a smaller font than the M6 making the values slightly harder to read.

The rear is markedly different. There are now separate connections for each input, and a ground lift switch. The switch has three positions; ‘lift’ in which the signal ground is disconnected from the chassis ground, ‘soft’ which connects the signal ground to chassis ground via a resistor and capacitor, and ‘direct’ which connects the signal ground directly to the chassis ground. The middle ‘soft’ position is intended as a middle ground, with the resistor and capacitor effectively blocking low-frequency hum while conducting RFI (radio frequency interference) to ground.

Also new are a pair of balanced (XLR) inputs on input 3. These join the balanced outputs to give fully balanced signal transmission throughout. Inputs 1 and 2 are single-ended, and there is a single-ended output to. Power is via a standard IEC inlet with a -40dB 100mHz RF filter.

The fully balanced typology is one of the aspects that make the M6x upgrade so exciting. A phono cartridge is an inherently balanced device, though few phono stages offer a balanced input and even fewer tonearms employ balanced cabling, at least externally. A balanced signal carries two signals, one normal and one phase-inverted. Any signal that is identical on the two lines is unwanted noise, as the desired signal (I.E the music) will be phase inverted. Thus noise can be filtered out, which is hugely important in a high-gain phono stage as the high amounts of gain required to amplify the tiny signal coming from a cartridge increase their susceptibility to noise. Noise can also be picked up by the cartridge itself and the tonearm cable, especially if the latter is improperly or inadequately shielded.

Most tonearms are wired for single-ended operation, whereby the cold (negative polarity) signal is connected to ground. For those with removable cables, a balanced conversion can be achieved with a custom cable, which connects the + and – wires coming from the cartridge to pins 2 and 3 of an XLR connector respectively. Pin 1 of the XLR cable (ground) is then connected to the tonearm ground. For tonearms with a fixed cable, assuming an RCA connector, an adapter must be made. The centre of the RCA plug must be connected to pin 2 of an XLR, the outer ring of the RCA plug to pin 3, and pin 1 can then be grounded. In doing so the signal becomes balanced.

Specs-wise the M6x is no less impressive than its predecessor with a signal to noise ratio > 101dB (MM) and 90dB (MC). SNR is the difference between the maximum level a component can accommodate and the noise level it produces. When I first saw the specs for the M6x I noticed some disparity in the quoted specifications for the two models. This was a result of a conflicting approach used by the engineering teams pre and post Musical Fidelity’s ownership transition. I will also admit with no small shame that I had miscalculated SNR based on the given spec, but as a result, a baseline was agreed that will be used going forward; adding the overload margin to the result of the signal to noise ratio measurement reference a 1-volt output (dBV).

The M6x adheres closely to the RIAA / RIAA-IEC standards with a frequency response flat to within 0.2dB (MM) and 0.25dB (MC). MM input impedance is still a fixed 47KΩ and MC input impedance is adjustable between 25Ω and 1200Ω. MM input capacitance is adjustable in sensible increments between 50 to 400PF, and MC input capacitance is fixed at 470PF. Total harmonic distortion at 1kHz is 0.005% (MM) and a slightly higher 0.002% (MC) . Neither figure would be of concern in a good line preamp, let alone a high-gain phono stage.

Input sensitivity for a 500MV output is 5MV (MM) and 500µv (MC), both at 1kHz. Outputs are via RCA and XLR with 500MV and 1V nominal outputs levels respectively, and 10V and 20V max output levels respectively. Both outputs can be used simultaneously with Musical Fidelity recommending the balanced outputs be used for lower noise and greater dynamic range.

The M6x slotted into my reference system in place of the M6. The only alteration to the setup being a balanced cable running from the outputs of the SL-1200G. Other turntables, namely my own ‘Project Glacier’ and a Lenco GL78 that was here for restoration during the review were connected via the single-ended inputs. In all cases, the inputs were configured to the recommended loading values for the Audio-Technica cartridges in use, with the 6dB gain disabled, and most of the time using the RIAA standard as opposed to RIAA-IEC.

My sample was an early production unit and was fresh from the box so I allowed the M6x a week or so to break in. I was keen to see how the M6V would compare to the M6 sonically, so set about a comparison with the two units side-by-side keeping the rest of the system identical, and using single-ended cables from the 1200G as the M6 lacked a balanced input.

The M6x has an appreciable reduction in its noise floor. The true extent of this improvement was masked by the noise of the line preamp and the self-noise from the system. It wasn’t until I connected some headphones to an extremely quiet headphone amplifier that I could fully appreciate just how quiet the M6x is. Any noise produced by the phono stage is far below the level at which it would be audible in any listening scenario, and orders of magnitude below the surface noise of any record on the best turntables. The M6 was quiet, but the M6x is noticeably quieter.

Improved dynamics were immediately noticeable. These are certainly a result of both the drop in noise floor and the new circuitry. The M6x doesn’t soften dynamics in any way and was able to demonstrate the full dynamic range of the best pressings in my collection. I’m confident that its dynamic range far outweighs that of any vinyl, as the vinyl format is intrinsically limited dynamically and that is further compounded by limitations in playback hardware. The M6 never appeared to squash dynamics and could throw out a big, bold stereo image, but the M6x takes both to new levels with infinitely expansive imaging in width, depth and height. Its dynamic performance makes loud or overcompressed pressings highly listenable even at high volume. There is no hint of the 0presence overload or distortion. It makes for a fun, enthralling experience in much the same vein as the M6, but with improvements in every area.

I was keen to see what differences the balanced connection could bring. The SL-1200G was fitted with an Audio-Technica OC9X-SL moving coil cartridge and wired with a high quality balanced cable constructed using professional-grade components; screened Van Damme cable and Neutrik plugs. The result didn’t differ in character from what I’ve described above but improved dynamic performance even further and lowered noise, with an appreciable drop in surface noise immediately apparent.

I’m struggling to sum up the M6x Vinyl. I hate using audiophile cliches in reviews but even if I did stoop to that level there are non that accurately describe the M6x. It is neither warm nor bright, neither coloured nor does it display any real character of its own. I own Musical Fidelity products because they have proven to be sonically neutral, low in noise and distortion and better dynamically than any source material.

The same is true for the M6x vinyl. Its predecessor, the M6 Vinyl had all of these traits too, but the M6x Vinyl improves upon them all and does so to a not insignificant degree. Sonically it is very similar in its overall character to the outgoing model, but with improvements across the board.

Along with its sonic improvements, the M6x vinyl brings welcome additions in the form of the balanced input and independent signal grounds with a configurable ground lift. Now one can truly realise the benefits of a balanced connection from input to output across the whole system, and the results speak for themselves.

The M6x vinyl is yet another exceptional product from Musical Fidelity. Beautifully designed and executed with a performance that under other brands would be considered superlative at well over 10 times the price. To me, musical fidelity embodies the true spirit of what high-end audio should be, and what it so often is not. Their products are well designed, well-executed and sold at a price that is reasonable given the components and technology inside. All to often audiophile components are built with astronomical profit margins a part of their design, and despite this many of them can’t come close to the quality of build or technical design that is to be found in current Musical Fidelity products, especially products like the M6x vinyl. That is why I use MF products myself, and that is why the M6x vinyl earns my unreserved recommendation.