Now available!
09.03.2023, this page is being re-written...
The PRO series will feature ±17V linear power supplies, balanced connections, and a new enclosure style that matches the SPARTAN 5, first released in summer 2022.
As the first PRO series product, the MC PRO moving coil phonostage features a discrete input amplifier that attains an SNR of 82dB against a 500µV 10Ω cartridge source, with adjustable low frequency cross-feed and gain. THD is less than 0.0005% throughout the audio band with an output exceeding 10V RMS.
MC PRO from the first production batch
A unique design, intended for low and very low output MC cartridges, the MC PRO has been realised through many months of research into ultra-low noise discrete hybrid amplifiers, and a new three-stage circuit architecture that avoids the compromises made by conventional moving coil combination phonostages. Consequently, it offers exceptional RIAA accuracy, vanishingly low distortion, and an even better signal to noise ratio than the best moving magnet amplifiers, despite amplifying a source voltage 10 times smaller. All of this is done using normal, readily available parts.
The MC PRO follows in the wake of the Spartan 10, using new techniques to improve over conventional phonostage architecture by carefully distributing gain through the signal path. It carries over the well-received low frequency crossfeed function that allows for significant reduction of vertical ‘vinyl roar’, while adding the option of a variable turnover so that the level can be adjusted according to taste. When enabled, an intermediate filter stage gently blends the two channels together, allowing a progressive cancellation of vertical rumble as the frequency drops. This can reveal previously unheard bass detail and seriously improve long listening sessions with headphones on.
Rear panel connections
BC327 audio amplifier transistors, chosen for their extremely low noise and superb linearity, make up the front-end of the servo-stabilised input amplifier, which uses the legendary NE5532 to provide drive and linearity, through a very low noise feedback network. Unlike other MC head designs, the head utilises the extra gain from the transistors, amplifying to over 10 times moving magnet level, while maintaining very low distortion. This makes the signal far more immune to noise and interference downstream of the head.
The head drives a low impedance, high precision, shunt-feedback equaliser using 1% tolerance polystyrene telecommunications capacitors. Opposed to a moving magnet amplifier, it can equalise the RIAA curve much more effectively at high frequency without a ‘correction pole’. As the equaliser operates with no common-mode voltage, and has to amplify 10 times less than it would from moving magnet level, it is exceptionally linear.
Downstream, the subsonic filter uses capacitors hand selected to within 1% of each other on each channel, ensuring excellent stereo balance and response flatness, purging component tolerance effects that have caused other subsonic-filtering phonostages to randomly fray the low end response. The last 6dB of gain are then made up after the subsonic filter, so as to prevent subsonic disturbances from eating into the final headroom.
Finally the MC PRO runs off a split ±17V linear power supply, ensuring noise free use for decades to come, with over 10V RMS of single ended output on tap. A startup mute relay is used to prevent several seconds of thuds and bangs as the head stabilises over 80dB of gain at low frequency. Gold-plated turned IC sockets are used to house the professional standard audio amplifiers that do most of the legwork.
| Parameter | Measurement |
|---|---|
| RIAA Accuracy | ±0.1dB, 40Hz to 22kHz |
| Channel balance | ±0.1dB, 40Hz to 22kHz |
| Signal to noise ratio (220Hz to 22kHz) | 81.5dB, ref 500µV, 10Ω cartridge |
| Total harmonic distortion | <0.0005%, 20Hz to 22kHz, at 21V RMS |
| Maximum output (20Hz to 28kHz) | 21V RMS (XLR), or 10.5V RMS (RCA) |
| Maximum input at 1kHz | 7.3mV RMS at 63dB gain, 2.3mV RMS at 73dB gain |
| Maximum input at 10kHz | 35mV RMS at 63dB gain, 11.3mV RMS at 73dB gain |
| Overload margin, ref 500µV, at 1kHz | 23.3dB at 63dB gain |
| Overload margin, ref 150mµV at 1kHz | 23.8dB at 73dB gain |
| Gain at 1kHz (RCA) | 63.17dB, 1440x, or 73.1dB, 4520x |
| Gain at 1kHz (XLR) | 69.19dB, 2880x, or 79.12dB, 9040x |
| Minimum load impedance | 1kΩ (RCA), 2kΩ (XLR) |
| Output impedance | 75Ω (RCA), 150Ω (XLR) |
| Input impedance | 120Ω |
| Subsonic filter | 23Hz, 3rd order, for -23dB at 10Hz |
| Low frequency crossfeed | 65Hz to 600Hz, -4.3dB to -21.6dB at 50Hz |
| Dimensions (W*H*D) | 172*60*155mm |
| Power consumption | 6W max powered on, 0.2W standby |
If you have any questions about this product, please get in touch. There is currently a waiting list for orders that will be fulfilled when the second production batch of units are made for official release (estimated January 2023).
Being rewritten...
Features
Now available in the UK! RIAA accuracy to ±0.1dB, third order subsonic filtering, mono switching, and variable low frequency crossfeed. A discrete, high performance head realises lower noise than any moving magnet system available, despite 10 times less signal level at the input. USA power supplies now available.
MC PRO front view
Pre-feature paragraph...
- HYBRID FRONT END
- Variable and defeatable low frequency crossfeed, cancelling low frequency noise to taste, revealing bass detail without loss of low-end
- GAIN SWITCH
- Mono switching, revealing detail by reducing noise and distortion on mono discs, making worn discs more listenable
- Class-leading RIAA accuracy to ±0.1dB, with no colouration exhibited by most other phonostages that struggle to meet ±0.5dB
- Exceptionally low distortion, less than 5ppm from the use of careful gain distribution in an original triple-stage topology
- LOW NOISE INPUT - DISCRETE
- Crystal clear high frequency reproduction through the use of HF GAIN DISTRIBUTION/HIGH GAIN HYBRID FRONT END
- 23Hz 3rd order subsonic filter, using hand-matched capacitors to eliminate low-end fraying in contemporary filter designs
- Fully balanced XLR outputs, allowing for a high quality line connection over a long length of cable for extra flexibility
- High quality ±17V split linear power supply with start-up muting for switching hash-free listening with over 10V RMS output
Rear panel, showing connections
Summary + video link if available...
Side view
Availability, ship worldwide, etc...
Build quality...
The MC PRO sits inside a compact sandblasted aluminium enclosure that fits neatly into most setups, allowing for close placement to the turntable. Thick aluminium panels add a pleasing weight to the unit, affording ample shielding to the electronics contained within whilst downplaying their exceptional performance, derived firstly from the innovative circuit architecture and in part from high quality components...
- All hand-soldered through hole technology, no cheap surface mount components
- Double sided, fibreglass, plated through hole PCB, with ground planes on both sides for very low cross-talk
- Film capacitors in the equaliser network and subsonic filter, distortion-free NP0/C0G ceramic parts filter RFI on the input
- All electrolytic capacitors are long life Panasonic FR and FM series, lasting for decades to come
- 1% tolerance metal thin film resistors in the audio path for high gain accuracy and excellent linearity
- Professional quality amplifier ICs in turned IC sockets, easy to change if destroyed by faulty electronics downstream
- Gold plated toggle switches rated for 50,000 cycles instead of the usual 10,000 cycles of cheaper push switches
- Precise conductive plastic track potentiometer for variable LF XFEED, rated for endurance at 100,000 cycles
- Panasonic telecoms grade output muting relays for many decades of high-reliability operation
- Gold over nickel-plated RCA and XLR connectors on the rear panel
- Large nickel-plated ground binding post that can accept banana plugs for easier connection
- 6mm CNC milled aluminium front panel, anodised for scratch resistance
- Stainless steel panel screws, all hex heads
Inside the MC PRO phonostage
Great care has been taken to lay out the PCB as efficiently and intuitively as possible, while at the same time minimising parasitics and crosstalk, so the MC PRO manages a triple stage design in a 172mm width enclosure. Unlike many other commercial products, the enclosure design was done after the electronics were perfected, leading to an understated design that eliminates as much dead space as possible, potentially reducing domestic friction!
Specification
A description of the specification and why it matters...
| Parameter | Measurement |
|---|---|
| RIAA Accuracy | ±0.1dB, 40Hz to 22kHz |
| Channel balance | ±0.1dB, 40Hz to 22kHz |
| Signal to noise ratio (220Hz to 22kHz) | 81.5dB, ref 500µV, 10Ω cartridge |
| Total harmonic distortion | <0.0005%, 20Hz to 22kHz, at 21V RMS |
| Maximum output (20Hz to 28kHz) | 21V RMS (XLR), or 10.5V RMS (RCA) |
| Maximum input at 1kHz | 7.3mV RMS at 63dB gain, 2.3mV RMS at 73dB gain |
| Maximum input at 10kHz | 35mV RMS at 63dB gain, 11.3mV RMS at 73dB gain |
| Overload margin, ref 500µV, at 1kHz | 23.3dB at 63dB gain |
| Overload margin, ref 150mµV at 1kHz | 23.8dB at 73dB gain |
| Gain at 1kHz (RCA) | 63.17dB, 1440x, or 73.1dB, 4520x |
| Gain at 1kHz (XLR) | 69.19dB, 2880x, or 79.12dB, 9040x |
| Minimum load impedance | 1kΩ (RCA), 2kΩ (XLR) |
| Output impedance | 75Ω (RCA), 150Ω (XLR) |
| Input impedance | 120Ω |
| Subsonic filter | 23Hz, 3rd order, for -23dB at 10Hz |
| Low frequency crossfeed | 65Hz to 600Hz, -4.3dB to -21.6dB at 50Hz |
| Dimensions (W*H*D) | 172*60*155mm |
| Power consumption | 6W max powered on, 0.2W standby |
Description text...
An image breaks things up...
More paragraphs...
Discrete input
Some text about BC327s, head amplifier, improvements over traditional circuits...
Maybe a close up shot?
New architecture
Some text explaining why the gain structure is superior to comination phono preamps...
Precision RIAA
So as to match the power bandwidth of music to the physical restrictions of vinyl recording, all records are cut with some form of equalisation that shapes the frequency response to fit into the limitations of the medium. This involves attenuating the low frequencies to stop the grooves cutting into each other on heavy bass notes, while boosting the high frequencies to overcome rising surface noise. The phonostage must perform the exact opposite process on playback, boosting low frequencies and cutting high frequencies to restore the original balance - hence the term 'equalisation'.
RIAA recording (red) and playback (green) curves
Since 1955, the RIAA standard has been used, which amplifies treble frequencies above 2122Hz and attenuates bass frequencies below 500Hz when the record is cut. The phonostage must precisely invert the curve at these points, as any error will result in unwanted boost or cut around these turnover points. Contemporary phonostages usually only manage an accuracy of ±0.5dB, which might initially look benign when we compare them against the sometimes drastic response variations of typical MM cartridges at the extremes of the frequency spectrum. Unfortunately, human hearing is much more senstive in the mid-range - right around the turnover points where most cartridges have a very flat response.
The ±0.5dB figure quoted so often - a result of using low-cost 5% tolerance capacitors in the equaliser circuit - can introduce a full 1dB of variation across the mid-range, audibly colouring the sound with its error signature. The effect is as if conventional tone controls are left askew at 1 and 11 o'clock position, considerably more harmful than the tone controls now shunned by many audiophiles ever were. Worse still, this can vary between the two channels, affecting stereo balance more than the cartridge itself while also shifting mid-range balance randomly around the sound-stage with frequency. Clearly, much better accuracy is needed for transparent processing...
Polystyrene telecoms capacitors in the equaliser amplifier
High-precision equaliser capacitors are not cheap, but the MC PRO seeks the very best, investing in 1% telecoms parts to reap an exceptional RIAA accuracy of ±0.1dB that beats the current standard by a factor of 5. Parallel 1% tolerance resistors are also used in the equaliser network for further tolerance averaging, making the specified ±0.1dB quite a pessimistic figure. The tiny RIAA error is well below the threshold of audibility in even the most imaginative estimates, so you can be assured of perfect transparency from a beautifully uncoloured frequency response with the best possible channel balance, delivering the original sound that the engineers intended when the record was cut.
Conventinal RIAA input amplifiers can require up to 60dB of gain below 50Hz; quite a challenge for most op-amps, and certainly not optimum for top-notch low-frequency distortion performance. By using a separate equaliser stage downstream of the input amplifier, the MC PRO takes this burden off the input amplifier. Doing so keeps distortion very low throughout the frequency range, compared to many other phonostages that see a rise in low-frequency distortion as the input amplifier runs out of corrective open-loop gain.
As the equalistion isn't performed by the input amplifier, it isn't constrained by the need for a high input impedance for the cartridge. The equaliser exploits this by using a current input shunt-feedback topology in a dedicated equaliser amplifier stage, instead of a conventional series feedback arrangement. The series feedback circuit can't track the RIAA curve at high frequencies below unity gain and requires an extra 'compensation pole' to take up the slack which can introduce its own error. The MC PRO's equaliser amplifier has no such problem, making for a very elegant circuit that tracks the curve accurately all the way into ultrasonic frequencies without any extra components in the signal path.
Too long; didn't read: ultra-precise replay equalisation five times more accurate than most competitors produces perfect channel balance and zero colouration!
Variable LF X-feed
Most of the noise on vinyl records is at low-frequency, which is unsurprising given that the RIAA curve boosts bass frequencies and most surface imperfections such as warps are rarely smaller than a centimetre in size. This 'vinyl-roar' has been known for a long time to almost disappear when mono mode is selected on the replay amplifier. The majority of low-frequency noise exists in the vertical up-and-down plane of the stylus's movement and is therefore cancelled when mono mode, only sensitive to lateral side-to-side motions, is enabled. Stereo low-frequency noise below 100Hz can be particularly distracting when listening through headphones with their near-perfect separation, as it unnaturally straddles the stereo field, causing listener fatigue.
Stereo (red), and mono (green) groove noise waveforms
Amplified waveforms of real groove noise, after 24Hz subsonic filtering, neatly illustrate the equal-and-opposite nature of low-frequency noise on stereo records. As shown above in the red waveform, the worst peaks of noise neatly move in the opposite direction, while the green mono sum reveals substantially diminished overall levels; a threefold measured improvement well worth having, to be precise. Regrettably, stereo sound is rather desirable in a HiFi system, so switching to mono isn't an option if stereo pressings are to be fully enjoyed unattended by this 'road noise'.
When records are mastered, all low-frequency information before 200Hz has to be carefully panned to mono. This is to prevent the stylus from jumping up out of the groove upon playback when excited by heavy bass notes, and also as a consequence of vertical range of motion being severely restricted. If the grooves are spaced well apart, they can move a good deal side-to-side with mono lateral modulation, but the groove can't move vertically up and out of its tiny cutting depth and into the thin-air above the record's surface with stereo information. Digital analysis of vinyl-rips support this, showing that all bass energy below 200Hz is mono.
Unfiltered (red), and LF X-feed (blue) groove noise waveforms
The MC PRO's low frequency crossfeed function gently blends the two channels together as frequency falls, cancelling much of the stereo noise, while preserving stereo separation in the more critical mid-range where the stereo image is generated. Because bass frequencies have to be panned to mono on mastering, no useful information is lost by blending to mono below 200Hz or lower. As shown in the above waveform of the same stereo groove noise, LF X-feed cuts back surface noise almost as much as switching to mono does, annihilating the worst peaks and easily halving the average level.
Although not a new concept, previous attempts at making an LFC circuit for vinyl playback featured in electronics magazines over the years, that used complicated summing and differential amplifier arrangements, all pass filters, and sometimes didn't even work in the first place! The MC PRO instead implements an elegant bridging arrangement that excludes any additional series components from the signal path. It can therefore be completely switched out of the signal path by a toggle switch on the front panel, satisfying purist sensibilities.
Continuously adjustable LF XFEED
As an upgrade over the original LF X-feed function on the Spartan 10 phonostage, MC PRO adds a continuous variable turnover, allowing users to decide from themselves the optimum balance of stereo separation in the lower mid-range and rejection of vertical low frequency noise. Increasing the turnover frequency increases noise cancellation, but narrows the stereo image slightly below 1kHz. When set to 140Hz, LF X-feed maintains 18dB of channel separation at 500Hz and 24dB of channel separation at 1kHz, better than most cartridges, and continues to extend to 30dB and beyond past 2kHz where the direction-finding ability of human hearing is most sensitive.
Too long; didn't read: LF X-feed cancels low-frequency 'vinyl-roar' while retaining the same level of stereo separation on the record at mastering, unveiling bass detail previously hidden in the noise. No more fatiguing 'road-noise' when listening with headphones, with a wide range of adjustment to suit all tastes!
Subsonic filter
Even a perfectly set up turntable will produce low frequency disturbances below 20Hz. Other sources of subsonic energy include the turntable bearing, the original cutting lathe, and potentially a resonance mis-match between the cartridge and tonearm. The greatest source of subsonic energy is the record itself, with small surface imperfections and warps being amplified 1000 times or so by the phonostage. This low-frequency noise usually intensifies where cartridge-tone-arm resonance occurs around 10Hz, and while not audible on its own, it creates a lot of trouble in any sound system if allowed out of the phonostage.
At normal listening levels, subsonic disturbances can easily push the unloaded drivers of bass-reflex loudspeakers well past their precious few millimeters of linear excursion, guaranteeing severe distortion while dissipating excess energy in the voice coil. The same is true for sealed loudspeakers and headphone drivers, delivering an ill-defined stereo image as the acoustic drivers wobble, with an unstable sound-stage and a 'shimmering' or 'tremolo' distortion effect as they amplitude modulate the wanted audio. Despite all this, many manufacturers still insist that filtering isn't necessary for high-quality listening...
Raw (red) and subsonic filtered (blue) vinyl waveforms
To prevent intermodulation artefacts, a truly high-performance phonostage should reduce subsonic disturbances by at least an order of magnitude in the troublesome 10Hz region, as shown in the waveforms above, taken from a typical LP. The MC PRO does just this, using a 3rd order high-pass filter with a cut-off frequency of 23Hz; enough to attenuate signals at 10Hz by a factor of 14, making certain that they can't cause any trouble further down the signal path. Fastidious tuning ensures that while subsonic energy is heavily reduced, the desired response doesn't change more than 0.1dB at 40Hz, preserving the ultra-accurate replay response of the precision RIAA network that precedes it.
Conventional subsonic filters have been lambasted by audiophiles for their in-band response variations that fray and distort the low frequency response. These are usually caused by picking the nearest component values to those calculated for the job, in tandem with the usual effects of 5% capacitor tolerances deviating the filter's tuning. This inevitably causes either undesirable peaking around and above the cutoff frequency with high group delay that muddies the sound, or premature roll-off that leads to thin bass. Channel balance can also suffer from tolerance effects, helping these essential filters to earn a bad reputation in some audiophile circles.
Hand-matched red epoxy-dipped polypropylene filter capacitors
The MC PRO solves the problem of component tolerance effects in the subsonic filter by using distortion-free polypropylene film capacitors, hand-matched to within 1% of each other, completely preventing tolerance effects from altering the response by more than 0.1dB from the ideal. By using one matched group for both channels, superb channel balance is maintained all the way down to 20Hz and beyond, while designing the filter iteratively for real-world component values keeps the response as close to ideal as possible right off the bat.
Unlike other subsonic filters, based around a unity-gain buffer with component values taken out of a textbook, the MC PRO implements the final 6dB of gain after the filter network. Applying the final gain after the subsonic filter stops subsonic disturbances from eating into the final headroom of the phonostage, as it does in conventional designs that apply all the signal gain ahead of the filter network. The distribution of gain away from the input and equaliser amplifiers also helpfully enhances the overall linearity of the design by increasing the overall feedback factor and therefore distortion correction of the first two stages. Common-mode input voltage on the filter amplifier is also halved, which further reduces its distortion.
Too long; didn't read: the strong subsonic filter attenuates subsonic disturbances by 14x, stopping them from destabilising the sound-stage, generating fluttering distortion in speakers and headphones, and wasting amplifier headroom. Unlike contemporary designs, hand-matched capacitors keep the response of the filter ultra-flat in the lower bass without any colouration, for deep, transparent, perfectly balanced bass with no thinness or muddying.
Mono switch
For the best results with mono pressings, a a mono function that sums both stereo channels together and puts the phonostage into mono mode is highly necessary. When enabled on mono discs, all stereo noise and distortion that sits irritatingly across the stereo field and draws the listener's attention away from the mono centre is cancelled. This yields a less fatiguing and more revealing listening experience. The mono function can also be used to improve heavily worn stereo discs by reducing distortion and surface noise enough to make them listenable again.
A-weighted stereo (red) and mono (green) groove noise waveforms
Many obtrusive clicks and pops exist as stereo information, and can be at least partially cancelled in mono mode, as demonstrated in the red and green waveforms of groove noise in a lightly used LP above. A-weighting removes the effects of low-frequency vertical noise to show a further improvement to the constant noise floor in the critical mid-range. The first click is almost eliminated completely, whilst the others are at least halved in amplitude - very useful for old mono discs that have been through the wars.
Noise and distortion cancelling mono switch
One of the most useful functions of the mono switch is its ability to instantly eliminate the jarring effects of fake 'reprocessed stereo', 'simulated stereo', and 'duophonic' processing on stereo re-releases of mono recordings. These apparently mangled pressings can be obtained for very low prices, as they're rightly shunned by most audiophiles as unpleasant to listen to. As such discs had to be mono compatible when released, the processing occurs only in the stereo difference and can therefore by removed in mono mode, stripping the reverb and phase effects away to reveal the original mono recording in the vast majority of cases.
Great reductions in distortion are also very possible on original mono discs, as well as later 78s that can be played back using the RIAA curve and a suitable stylus, that usually feature heavy vertical wear from the almost non-existent vertical compliance and heavy tracking force of mono cartridges of the era. This vertical wear distortion appears mainly during loud passages, generating stereo tearing artefacts that glaringly contrast against the mono source material, destroying dynamics and clarity.
Mono sum (green) and cancelled distortion (red) waveforms
By subtracting the stereo channels from each other to generate the unamplified red distortion waveform, while summing them to produce the green waveform in the above image, we see just how strong vertical distortion can be in practice on a visually pristine 1960s mono disc. Only a modest uptick in recorded level causes this highly unwelcome addition to jump savagely out of the noise floor and ruin the enjoyment and impact, with the distortion reaching a third of the level of the wanted audio. Luckily, the green mono waveform axes all of this rubbish, for distortion-free listening that conveys all of the detail in the loud passages otherwise masked by the distortion.
Too long; didn't read: if you have mono LPs, singles, 78s, or heavily worn stereo discs, the mono switch will halve surface noise and massively reduce distortion, unclouding the sound and allowing you to rediscover new details on these discs.
Balanced output
For extra versatility, the MC PRO features an inherently balanced output, permitting the total cancellation of hum and common mode interference over a long length of cable between its output and the line input of the next component in the signal path. This, along with its compact size, allows it to be placed as close to the turntable as possible without having to worry about the length of the line output cable. The fully differential output also produces a doubling of both signal level and headroom on the line connection, further increasing immunity to interference and improving the signal-to-noise ratio of the balanced input on the other end.
Chassis grounded balanced XLR outputs
Complementing the single-ended RCA outputs, the gold-plated XLR connections on the rear panel feature a chassis-grounded shield for extra immunity from radio frequency interference. With an output impedance of 75Ω on the hot and cold sides of the connection, the total differential output impedance comes to just 150Ω; low enough to minimise insertion loss into a standard impedance balanced input to less than 0.1dB. While the standard differential input impedance for balanced line inputs used to be an easy-to-drive 10-50kΩ, many products released over the past few years have reduced this all the way down to as low as 2kΩ.
Reducing line input impedance by a factor of five from the previous standard may be great for reducing resistor voltage noise in the differential input amplifier and creating a tidy input noise figure for the spec sheet, but it comes with a heavy price in practice. New low-impedance 2kΩ balanced line inputs can pose a serious problem to many balanced outputs on the market designed for the conventional 10Ω, overloading their outputs by drawing much more current than they were designed for, reducing the available headroom, and increasing insertion loss to over 2dB when connected to a legacy 600Ω line output circuit.
Back-to-back output capacitors and muting relay
The trend toward low-impedance balanced line inputs is duly accounted for in the MC PRO's line output. Output impedance is kept low enough so that insertion loss stays below 0.7dB when driving a 2kΩ input. The ample drive capability of the 5532 line output amplifiers ensure up to 20V RMS of differential output without any increase in distortion while driving this challenging load. Regardless the equipment downstream, the MC PRO will always deliver a clean, distortion free performance.
A high-quality, high-reliability Panasonic telecoms relay, rated for medical applications, prevents turn on transients from escaping onto the line output when the MC PRO is switched on and off. The line output is DC decoupled using back-to-back output capacitors for low-frequency distortion cancellation when driving potentially heavy loads and affords full protection (in both directions!) also from 48V phantom power, should it be erroneously applied to the line output.
Too long; didn't read: fully balanced XLR output connectors double the signal level, and afford total common mode noise and hum rejection on the line connection. 5532 line drivers easily drive challenging line inputs as low as 2kΩ to full level, for undistorted sound into the most challenging modern inputs.
Linear power supply
Many small phonostages today use an external switching power supply that can inject nasty audio frequency currents straight from the mains into the audio ground path between the phonostage and power amplifier, resulting in unpleasant buzzes, hums, and whines. In most cases this adds a most unwelcome accompaniment to the music. Switchers also have a very undesirable habit of allowing the 0V output 'ground' to 'float' at 80V RMS or so; more than enough to damage sensitive line inputs when hot swapping equipment. Switching supplies are also notoriously unreliable as they combine electronics and heat together into a small form factor...
External linear AC transformer
By using an external linear transformer to interface with the mains, the MC PRO affords far better isolation from the mains than switchers, without any high frequency switching noise or ground path current. The transformer's double insulation and leakage capacitance also block off a potential route for ground loops. As the transformer is external its troublesome magnetic field stays outside of the enclosure and well away from the sensitive electronics contained within, where they might induce hum. External transformer based power supplies, while not as cheap or convenient as switching ones for a low parts count and corresponding low cost, have an excellent track record for longevity and are easily replaced in the highly unlikely event of failure.
Split linear ±17V power supply
The low frequency 9V AC transfomer output is internally rectified and converted to ±17V DC, using a precise Zener diode referenced voltage regulator circuit that allows the amplifier stages it powers to swing almost 30V of output peak-to-peak; their maximum safe possible output and over 50% more than a common 24V DC switcher can provide on a good day. Splitting the power rails between +17 and -17V keeps the non-linear amplifier power currents between these opposing points and out of the sensitive 0V audio reference where they could induce distortion. Another benefit of splitting the power supply into a pair of separate power rails is that there is no need to generate a DC 'bias' voltage from them that gets injected into the audio path, removing another potential source of trouble.
Reviews
Independent audio equipment reviewer, Ashley Cox of Audio Appraisal recently gave the MC PRO a glowing review, confirming the practical benefits of its features after 3 months of continuous listening...
I could delve into my box of audiophile cliches and tell you how the MC Pro has air, rhythm, timing, detail etc in spades. Or I could triple the length of this article listing the records I’ve played through it and give you a play-by-play commentary on how the MC Pro lifted each to new heights. Or I could simply tell you that the MC Pro has been a key component in realising the best sounds I have ever heard from a vinyl record. It’s that simple.
I have spent the past three months trawling through every phono stage on the market, trying to find something with a specification that comes close to that of the MC Pro. In that time I have played numerous albums with several cartridges, and not once has this little box provided anything less than stellar performance. My search of the market left me empty-handed. The MC Pro currently offers the finest technical performance of any phono stage I can find on the market at any price. It demonstrates that real-world performance is not wizardry or pseudoscience, but competence and ability.
If you’re stepping onto the MC ladder and considering a step-up transformer to use with your existing phono stage, buy the MC Pro instead. If you’re at the top of the MC ladder and you’re eyeing up some multi-box, five-figure esoterica that needs a rack of its own, consider its technical performance and buy an MC Pro instead. The MC Pro by Michael Fidler earns my whole-hearted, entirely unreserved recommendation.
Ashley Cox, Audio Appraisal
