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Thermionic Culture Snow Petrel

Dual-channel Microphone Preamplifier
By Hugh Robjohns

Thermionic Culture Snow Petrel

Thermionic's latest valve preamp offers bags of gain and plenty of analogue warmth. Is this the perfect partner for your ribbon mics?

Thermionic Culture's chief designer Vic Keary has a fascinating reputation for using valves and circuit topologies that aren't conventionally associated with high-quality audio, yet which always deliver the goods, sonically and technically. His latest design, the Snow Petrel, is a two-channel valve mic preamp. It's a 'high-gain' design with very low noise and distortion, intended primarily for use with low-output ribbon mics.

Vic told me that the inspiration for the Snow Petrel lay in a previous career — he enjoyed using the classic Coles 4038s for brass and drums but found that most mic amps and mixers of the time had too much noise and distortion to enable their use on quieter instruments. So the Snow Petrel was designed specifically to enable low-output mics like the 4038 to be used on quiet sources. That sounds simple enough, but Vic has high standards, and it took him five years, two unsuccessful previous versions, and a rather unusual circuit design to develop it to his satisfaction!

Of course, the Snow Petrel is not a one-trick Antarctic-gull: it is equipped with both switchable phantom power and input attenuators, and it can work with dynamics and high-output capacitor mics in a wide range of different applications just as competently as it can with passive ribbons.

The Tour

A hefty 2U rackmounting device, the Snow Petrel weighs 6kg and extends 290mm behind the rack ears. It consumes 30W of power but the case is well ventilated at the sides, rear and top, so there's no requirement for a ventilation space above the unit. Rear-panel connections are minimal: two pairs of XLRs for the transformer-balanced mic inputs and line outputs, plus a standard IEC (C14) mains inlet with integrated fuse holder. There's also a voltage selector switch for 115 or 230 V AC mains supplies.

The visual styling is typical of Thermionic Culture, with the front panel carrying crisp white legends on a glossy black-painted background. Five chicken-head rotary controls and four toggle switches are provided for each channel, and another chunky toggle switch with a large green status lamp switches the unit on/off.

Another pair of toggle switches, each with red status LED, engage each channel's phantom power. These 'secure' switches have to be pulled out before they can be moved, preventing accidental operation — a feature intended to protect delicate ribbon mics. They won't help if phantom was left on accidentally in a previous session, of course, but I spent an entire BBC career 'hot-plugging' Coles 4038 ribbons (phantom power is present permanently on most BBC...

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Published January 2020