Slate Pro Audio Fox Preamp Review

Oct 1, 2011 9:00 AM, By Kevin Becka



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The Fox’s Combo/Normal settings allow you to switch between four different input/output stages.

The Fox’s Combo/Normal settings allow you to switch between four different input/output stages.

Steven Slate produces both software and hardware in his product line. The Trigger Drum Replacer and Virtual Console Collection, the former reviewed in Mix (January 2011), plus its FG-X Mastering Processor fall under the Slate Digital moniker, while hardware—including the Dragon Dynamic Processor and Fox preamp reviewed here—sit under the Slate Pro Audio division. The Fox preamp ($1,799) is a solidly built unit with a hefty linear power supply. Its price and features put it squarely in the boutique realm, giving you a welcome range of choices when recording.


These four bench tests (download pdfs) show the following stats for each of the four input/output path selections (Modern/Normal, Vintage/Normal, Modern/Combo, Vintage/Combo): gain, THD + N ratio, frequency response, crosstalk and interchannel phase.





Slate Pro Audio Fox In Use Video

Slate went the extra mile with the Fox. Inside the heavy steel chassis, all connectors, switches and rotary controls are top-of-the-line—even the front panel is “foxy,” sporting a raised, semi-gloss pattern. Features include a DI input, 12-position gain knob in 5dB increments and continuously variable rotary output control, which is at unity when wide-open. To avoid confusion, I would like to have seen zero labeled at full gain rather than the 0 to 10 as screened on the panel. Other features include switches for phantom power, -10dB pad, polarity flip and mic/instrument settings, as expected.

Where the Fox steps beyond the norm is its Vintage, Modern, Combo and Normal settings. This feature switches the input and output paths of the preamp between four options. I got the rundown on the tech from Fox circuit designer Tim Caswell, who went deep into the design for Mix. Modern/Normal is transformerless, starting with a matched transistor pair followed by three Burr-Brown op amps, with a DC servo to eliminate the output coupling capacitor. This is followed by a line driver stage with a Burr-Brown op amp with MJE 182/172 transistor current boosters, also DC-servo’ed. In Vintage/Normal, the input stage is the Class-A C-4018 Altran transformer followed by a C-4000 Altran line driver.

You can also split the Vintage vs. Modern input/output stages with the combo switch. Vintage/Combo is the transformerless preamp followed by the Class-A/4000 transformer line driver, while Modern/Combo has the 4018 input stage followed by the tranformerless Modern output. These four options provided a great way for me to A/B/C/D the preamp on any application. You can also play sonically with the Input vs. Output by bringing down the output and driving it harder with elevated input levels, making for endless sonic possibilities.

When I performed EIN tests on the Fox using an Audio Precision APx525 audio analyzer, I was able to confirm the specs that Slate printed in its manual. The Modern mode is dead-flat out to 20 kHz, and I found that the Vintage mode rolled off well before 20 kHz, which my ears confirmed.

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