Mobile Fidelity - MasterPhono Phono Preamplifier

MoFi’s flagship all-analog phono preamplifier: a fully discrete balanced design with a current-mode transimpedance MC input, passive RIAA using NOS capacitors, three switchable inputs including XLR, and VU meters that double as a cartridge calibration tool.

Created alongside renowned audio engineer Peter Madnick, the MasterPhono is the result of more than a year of research, development and prototyping, and it exists for one reason: to replicate in playback the sonic integrity Mobile Fidelity Sound Lab builds into its vinyl reissues. Every stage is all-analog and fully discrete, with servo control and DC coupling in place of the coupling capacitors that colour so many phono stages.

The centerpiece is the current-mode transimpedance input stage, developed specifically for moving-coil cartridges. Its near-zero input impedance damps the cartridge automatically regardless of the generator’s internal impedance, and it is immune to cable capacitance and RF — which also means the resistive loading options do not apply when you are using that input. Three inputs are switchable from the front panel: the transimpedance current input on RCA or XLR, a balanced XLR voltage input, and a single-ended RCA voltage input, with two ground connections provided.

For the voltage inputs there are nine resistive loading positions plus a Custom setting, which accepts user-supplied loading plugs in rear-panel RCA jacks so you never have to open the chassis. The 47k position comes with a fixed 150pF of capacitance; no other capacitance value is offered, which is worth knowing if you run a moving magnet that wants a different total load.

MoFi describes the construction as dual-chassis, and that is accurate but internal — it is one enclosure holding two ground-isolated sub-chassis between shared wooden sleeves, keeping power and signal apart. There is no second box to find shelf space for. RIAA correction is passive, using new-old-stock capacitors, and the audio circuitry runs on cascaded voltage regulation.

The front-panel VU meters have a second function. Switched to calibration mode the unit sums the two channels with one inverted in phase, so playing an out-of-phase track from a test record and rotating the cartridge for a minimum reading sets azimuth by electrical channel balance. A test record is required and is not supplied. A remote handles input selection, gain, mute, mono, meter display and the subsonic filter from the listening chair. Available in Walnut or Black, and backed by five years parts and labor.

Features

• Current-mode transimpedance input stage optimized for moving-coil cartridges
• Near-zero input impedance automatically damps the cartridge, immune to cable capacitance and RF
• Three front-panel switchable inputs: transimpedance current input on RCA or XLR, balanced XLR voltage input, single-ended RCA voltage input
• Balanced XLR outputs as well as RCA — electronically balanced, DC coupled and servo controlled
• Dual-chassis construction within a single enclosure, isolating power supply from signal
• Fully discrete balanced circuitry with servo control, DC coupled throughout
• Passive RIAA equalization using new-old-stock capacitors
• Nine switchable resistive loading positions plus Custom loading via rear-panel RCA plugs
• Dual-function VU meters for signal monitoring or cartridge calibration
• Remote control of input, gain, mute, mono, meter display and subsonic filter
• Cascaded voltage regulation for an ultra-low noise floor
• Five years parts and labor, made in America

Specifications

• Type: All-analog MM/MC phono preamplifier, flagship
• Gain: Selectable 40dB, 50dB, 60dB, 70dB (MM or MC)
• Loading: 15Ω, 30Ω, 50Ω, 75Ω, 100Ω, 500Ω, 1kΩ, 10kΩ, 47kΩ +150pF, and Custom. These apply to the voltage inputs; the current-mode input needs no resistive loading
• Capacitive Loading: 150pF, fixed, bundled with the 47kΩ position. No other value is offered
• Custom Loading: User-supplied resistive loading plugs into rear-panel RCA jacks — resistive only, no chassis opening required
• THD (A-weighted): MM 10mV @ 1kHz, low gain — 0.005%; MM 10mV @ 1kHz, high gain — 0.005%; MC 1mV @ 1kHz, low gain — 0.010%; MC 1mV @ 1kHz, high gain — 0.013%
• RIAA Accuracy: ±0.05dB
• Frequency Response: 10Hz–50kHz ±0.20dB
• Maximum Output: 10V RMS @ 1% THD
• Inputs: Transimpedance current input on RCA or XLR; balanced XLR voltage input; single-ended RCA voltage input. Two ground terminals
• Outputs: Balanced XLR and single-ended RCA
• Chassis: Dual-chassis construction inside a single enclosure — power and signal isolated with separate grounding. There is no separate power supply box
• Meters: Dual-function VU meters — signal monitoring, or cartridge calibration. Azimuth setting requires a test record with an out-of-phase track, not supplied
• Remote Control: Input, gain, mute, mono, meter display, subsonic filter
• Finishes: Walnut or Black
• Dimensions: Approximately 17″ W x 3.5″ H x 15.75″ D (432 x 89 x 400 mm), covering the whole enclosure. MoFi does not publish dimensions; this figure is from its US distributor and one review source gives the width as 17.5″
• Weight: 15 lbs (6.8 kg)
• Warranty: Five years parts and labor
• Origin: Made in America
• Note: MoFi publishes no signal-to-noise ratio, output impedance or channel separation figure for this model. Distributor-quoted signal to noise is 93dB (MM) and 85dB (MC)