MM PRO Phono Preamp by Michael Fidler and Classic Audio

Michael Fidler and Classic Audio are synonymous with making quality phono preamps — a.k.a. phono stages, depending on your nomenclature preferences — as the company’s respective PRO and Spartan series can readily attest. Fidler’s latest offering, the MM PRO, is ready for system-integration duty regardless of which side of the Pond you reside.

The MM PRO consists of new circuit architecture that’s intended for moving magnet (MM) and high-output moving coil (MC) cartridges. A new, “active loading” input amplifier design is said to yield a lower MM S/N than previously possible with passive cartridge loads via the addition of noise-cancelling low-frequency crossfeed, 3rd-order subsonic filter, precision RIAA equalization, mono switch, and balanced output.

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Handmade in Kent, England, and utilizing all through-hole technology, the MM PRO sports a 42/52dB gain switch to accommodate lower levels from HOMC cartridges, while socketed NE5534 input amplifiers, especially chosen for their cartridge impedance matching current to voltage noise ratios to attain a level of noise performance said to leave the standard 47kΩ passive cartridge-loading resistor as the next greatest source of noise on the input.

In Fidler’s own words, the following explanation: “A 560kΩ resistor, as used in the MM PRO, has over three times less current noise than a 47kΩ one, so by driving the other end of it (usually connected to ground) with an inverting amplifier at 10x gain (hence the term ‘active loading’), it is made to behave like a 51kΩ resistor. This gives the desired input impedance of 50kΩ with three times less current noise, and an unweighted signal-to-noise ratio of 79dB with a real-world cartridge connected against 5mV. The easiest way to view this is that the inverter’s amplification increases the signal-to-noise power across the resistor for lower overall input noise than possible, even with a noise-free input amplifier.”

RIAA equalization for the MM PRO has been implemented to 0.1dB. Continuously variable, fully defeatable low-frequency crossfeed is also present. A 23Hz 3rd order subsonic filter attenuates 14 times at 10Hz, with hand-matched capacitors for ultra-flat in-band response and used to prevent subsonic energy from destabilizing and overloading equipment further down the signal path and generating intermodulation distortion in speakers. For cancelling stereo-field noise and distortion on mono pressings, a mono/stereo toggle switch is included on the front panel.

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The uncompensated input amplifiers limit high-frequency feedback, while gain distribution in the triple-stage design results in less than 0.0005% distortion. The balanced output can drive 2kΩ line input to 20V RMS “without any degradation in linearity” (their words), made possible via ±17V internal power supply rails. The MM PRO uses a linear split power supply. Panasonic electrolytic capacitors are used throughout, alongside medical-grade output muting relays.

The MM PRO is currently available to order worldwide direct from Classic Audio in the UK, with an SRP of $800 for the U.S. (import duties may apply), £600 in the UK, and €700 for EU countries.

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The above SRPs includes shipping to the respective regions as noted (other region prices will be calculated at the point of order). To date, Classic Audio deliver their products direct to customers in the U.S., EU, Australia, and India. Power supplies for 115V and 220V regions are also available to accommodate for all different mains voltages.

For more about the MM PRO, go here.
To order an MM PRO direct from the manufacturer, go here.


$800 U.S. (£600 in the UK; €700 for EU countries)

Features & Specs
RIAA Accuracy: ±0.1dB, 40Hz to 22kHz
Channel balance: ±0.1dB, 40Hz to 22kHz
Signal-to-noise ratio, ref 5mV MM): 79dB; MM cartridge load, flat 220Hz to 22kHz
Signal-to-noise ratio, ref 2mV HOMC: 77.5dB; 200Ω input load, flat 220Hz to 22kHz
THD: <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: 82mV RMS at 42.4dB, 26mV RMS at 52.3dB
Maximum input at 10kHz: 400mV RMS at 42.4dB, 125mV RMS at 52.3dB
Overload margin ref 5mV, at 1kHz: 24.3dB at 42.4dB gain
Overload margin ref 2mV, at 1kHz: 22.3dB at 52.3dB gain
Gain at 1kHz (RCA): 42.39dB, 132x, or 52.30dB, 412x
Gain at 1kHz (XLR): 48.41dB, 264x, or 58.32dB, 824x
Minimum load impedance: 1kΩ (RCA), 2kΩ (XLR)
Output impedance: 75Ω (RCA), 150Ω (XLR)
Input impedance: 50kΩ / 120pF
Subsonic filter: 23Hz, 3rd order, for –23dB at 10Hz
Low frequency crossfeed: 65Hz to 600Hz, –4.3dB to –21.6dB at 50Hz
Power consumption: 6W max powered on, 0.2W standby
Dimensions (w/h/d): 172 x 60 x 155mm


JACK L's picture


Features alone: with unique "active loading" for input cartridge, balanced outputs with 21Vrms O/P, 3rd order subsonic filter, LINEAR power supply, is a huge deal !!! Hard to find a phonostage with better features so darn cheap in the marketplace nowadays let alone made-in-England.

To enable to build such premamp sooo low cost is using op-amps throughout, IMO.

My only reservation is the sonic quality of phono-pramps using op-amp chips which inherently comes with tons of internal gains with loop feedbacks due to the built-in bipolar junction devices. Yes, external circuit design can make good on bench measurement.

But how good it would sound could be another story !

As a hobby audio amp designer/builder for decades, I would not use any bipolar junction devices, e.g. transistors, FETs, to build my amps due to the inherent non-linearity of the P/N junctions inside the device. Non-linear devices geneate intermoduation distortion. This is physics.

That said, for vinyl beginners or tight-budgetted audio consumers, why not go for it.

Not many vinyl addicts like yours truly can hear the difference, anyway.

Hearing is believing


barfle's picture

They are reviewing equipment that mortals can afford!

Seriously, this is a very, very welcome trend. I hope it continues.