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Slate Pro Audio Fox Preamp Review


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.

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.

I had the opportunity to hear the Fox used across a number of applications. On a pair of U87s placed as a spaced pair over a drum kit, Vintage/Combo gave the best results. Switching to the Vintage/Normal alone made the snare sink in the overall drum mix and dulled the overheads. Switching to solely the Modern/Normal setting brought back the top end and the snare, but something was lost in the snare hit’s beefiness. The Combo brought that certain chunkiness that the vintage circuit brings to the kit on transient hits of the snare and toms while offering the clarity of the modern input.

Next I cut the same drum kit/drummer on two back-to-back sessions. On the first session, I used the Fox on the kick (Shure Beta 52) and snare (Shure SM57). I switched between all four input/output combos and settled on Modern/Combo for this application. It brought out the attack of both drums while giving me plenty of low and mid-low beef, making these core instruments sound great in the overall mix. In the next session, I switched the Fox to mics on the up and down of the kit’s Lo-tom (Sennheiser E602/AKG D-112). I had previously used an SSL 4000 preamp on the tom earlier in the day when I had the Fox on the kick and snare, and noticed the difference immediately when I switched to the Fox. It was like a blanket was lifted off the tom in comparison to the morning session, making me pine for more Foxes.

I recorded bass through the Fox’s DI input with the player plugged directly into the unit, making the long run to the control room at line-level. The only signal flow difference with this input is that the 4018 transformer is bypassed on any setting—the output of the FET instrument buffer goes directly into the Vintage output’s 4000 transformer or the Modern’s transformerless output only. I gave the player a quick tutorial on the gain and four settings, which he switched through while I listened in the control room. Both of us agreed that Vintage/Normal was the best combination for the bass, offering plenty of warmth and body to the instrument while still sounding well-defined in the upper midrange. I barely needed any gain in this application, running the output at unity and the gain only at the second detent.

Next I cut various hand percussion using the Fox to power an sE Electronics Voodoo VR1 microphone. Because of the quiet nature of some of the shakers I was cutting, plus the fact that the VR1 is passive, the Fox had to be fairly cranked to achieve the levels I desired. I was pleasantly surprised that even wide-open, the Fox was whisper-quiet. I cut the percussion in Normal/Modern mode, which was open on the top, had an intimate presence and sounded great.

For the next test, two mics were A/B’d on an acoustic guitar through the Fox. One channel powered a Peluso U47 capsule with his BV8 transformer, and the other channel juiced a Peluso C12 capsule with his BV11 transformer. Both mics were pointed at the junction of the guitar’s neck where the fretboard meets the body. Both mics sounded full and delightfully twangy in this application. On the Fox, Normal mode provided the starkest difference between the two mics. Switching to Modern brought out the harmonics of the strings while the Vintage setting brought the top-end emphasis down in favor of the body of the guitar. Kicking in Combo mode offered completely different results, with Modern giving the best sound: plenty of top and great body combined. The Combo/Vintage mode was a bit darker and not right for the track.

No matter what I tried it on, the Fox preamp gave me plenty of sonic options and always sounded great. The only problem I had was with the Manual: It was misleading, containing information about the Combo/Normal switching that contradicted the info I got from circuit designer Tim Caswell. He assures me that this is being addressed, and the manual is being rewritten to reflect the proper signal flow. Other than that, the Fox is highly recommended. It offers many clean or dirty gains, depending on your Normal vs. Combo choices, giving a wide palette of sonic possibilities from which to choose.

Kevin Becka is


’s technical editor.

Click on the Product Summary box above to view the Slate Fox product page.