Analog Gear News

Michael Fidler is a bonafide classic audio maestro, and he knows how to build phono preamps about as good as anybody can. To that end, the latest phono preamp offering from Michael Fidler and Classic Audio, the Spartan 15 Mk 2, is said to have evolved the standards set with company’s prior Spartan 15 and Spartan 10 double-stage preamps.

The Mk 2 (a.k.a. the MKII) retains the measured performance and sound goals of its forebears while adding refinements in circuitry, features, and enclosure design, all without a price increase. Hand-assembled using through-hole components in the South of England, the Spartan 15 Mk 2 is said to deliver a digital-audio level dynamic range of over 110dB, from the “ultra-quiet background” of its Japanese input amps to its 10.5V RMS max output level.

Panasonic electrolytic capacitors and 1% metal film resistors are deployed to ensure long-term stability, while 1% tolerance film capacitors in the active RIAA stage hold replay to ±0.1dB of the reference curve, eliminating midrange coloration and channel imbalance. A key upgrade for the Spartan 15 Mk 2 is the expansion of the low-frequency crossfeed function, blending the two stereo channels to mono at lower frequencies to reduce audible rumble, without loss of stereo separation in the midrange.

A center-off toggle switch on the Mk 2 offers selection of 100Hz and 200Hz turnovers, allowing adjustment of the reduction. The mono switch also remains to collapse distracting stereo-field noise and distortion on mono or damaged pressings. The Mk 2’s new, rounded aluminium chassis shows off a streamlined appearance that blends into the front and rear panels more seamlessly.

The unit’s enclosure parts are bead-blasted, plated, and finished in Berkshire, England. Front and rear panel graphics are durably laser-etched in-house with Classic Audio’s CO2 engraving system for enhanced quality control. Audio performance is enhanced by the 3rd order 22Hz subsonic filter, said to “prevent the slightest destabilization of loudspeaker and headphone drivers in the troublesome 10Hz region.” Hand-matched polypropylene film capacitors in the filter network ensure flat response down to 40Hz with less than 0.1dB variation.

The 40.8dB (110x) gain is shared between the input and output amplifier stages, lowering input-stage workload by 70%, to keep distortion under 0.0006% from 40Hz to 22kHz. By making up the final 10dB of gain after the subsonic filter, these surface disturbances are neatly excluded from the final headroom.

The Spartan 15 MKII continues to use a 9V AC external transformer-based linear power supply, ensuring the power transformer’s magnetic field stays well enough away from the sensitive analog circuitry inside the small enclosure. In contrast to low-cost switching supplies, the linear transformer operates with far lower noise. A new power supply over-voltage protection circuit guards against the use of incorrect adapters.

Internally, the split ±17V rails are regulated with precise reference diodes, providing fast and stable headroom independent of temperature. Both positive and negative rails are full-wave-rectified, ensuring no direct current can unbalance the transformer core. By splitting the rails, the design avoids injecting non-linear power currents into the ground, preventing power currents from contaminating the reference point. It also allows all amp inputs to be referenced to 0V, precluding any rail-dependent DC biasing. Thanks to this architecture, the circuitry stabilizes in seconds after power-on, and a Panasonic relay mutes the line outputs to suppress turn-on and turn-off transients.

The standard Spartan 15 Mk 2 unit comes in black, while limited-edition models are also offered in dark gray, deep blue, and red-fronted black finishes (some of which can be seen throughout this story).

Finally, the SRP for the Spartan 15 Mk 2 phono preamp by Michael Fidler and Classic Audio is $490 for the U.S., £360 for the UK, and €440 for the EU. Payments are also accepted in cryptocurrency, as well as in Australian and Canadian dollars. Please note that import duties or taxes may apply, depending on your region.

To read Ken Micallef’s July 30, 2024, review of the MM PRO by Michael Fidler and Classic Audio phono preamp, go here.