Phonostages — MoFi Electronics ULTRAPHONO

The UltraPhono from MoFi Electronics combines a solid-state phono stage with a Class A headphone amplifier. Its circuit was developed with help from Tim de Paravicini, the engineer behind the Gain2 Ultra Analog cutting system of Mobile Fidelity Sound Lab. The unit is handcrafted in the USA at the dedicated Michigan facility of Mobile Fidelity, and MoFi lists it at USD 499. In the MoFi range it sits above the StudioPhono, from which it differs mainly by the headphone section and a signal to noise ratio that the brand's comparison puts 6 dB higher.

Key specs that matter

Selectable gain of 40, 46, 60 or 66 dB suits both cartridge families, from high output moving magnet to low output moving coil. The moving magnet input presents 47,000 ohms, and moving coil loading is selectable between 75, 100, 500, 1,000, 10,000 and 47,000 ohms, with input capacitance at 100 pF. MoFi rates total harmonic distortion below 0.006% for moving magnet and below 0.055% for moving coil. The headphone output is rated at 8 V RMS maximum, 62 ohms and 1.5 W per channel, and MoFi sets the minimum headphone impedance at 10 ohms.

Engineering and use context

Gain and cartridge loading are set with toggle switches on the bottom of the case, so changes do not require tools. A mono switch on the front panel sums the channels for mono records, and a subsonic filter cuts the infrasonic output caused by warped discs and by poor turntable isolation. The headphone stage runs in Class A and is controlled by a 31-step volume control with 2 dB per step, giving a 62 dB range, while a mute switch attenuates the output by 90 dB. Power is supplied by an external balanced unit, which MoFi uses to lower noise in the phono circuit, where cartridge signals are only millivolts in level. Inside, MoFi uses hand-selected parts throughout the signal path.

Pairing

The loading choices cover low impedance moving coil cartridges at 75 or 100 ohms as well as high output types that prefer the standard setting, so the stage can be set to what a cartridge maker specifies. For moving magnet use the lower gain settings apply, and the upper settings serve low output moving coil designs. The line output feeds any amplifier input without phono equalisation, and headphones can be driven straight from the phono signal without a separate amplifier.

Alternatives

The MoFi StudioPhono offers the same gain steps and moving coil loading in a smaller case without the headphone amplifier.