Coil Audio CA-286 Preamp

Modular, Rich-Sounding Old-School Tube Preamp
The CA-286 uses NOS EF86 vacuum tubes and features interchangeable transformers.
Sound Byte

The Coil was a pleasure to use wherever it was applied, bringing rich tone and surprising harmonic content to a variety of instruments.It excelled on electric guitars, electric bass and drums.

The CA-286 is a tube mic/line amplifier built in a retro style inside and out. It looks like nothing else you’ve seen and is solidly constructed with special touches like its two-stage on/off toggles to keep from shocking the tubes. Turning on the #1 switch first, then waiting a few seconds to flip the #2, will keep the unit happier over time.

Each unit offers five rotary controls: input, output, negative feedback (NF), Hi, and Low. Removable input and output transformers are easily accessible on the rear of the unit. From the manual: “Each module uses custom interchangeable transformers, NOS ‘Paper and Oil’ capacitors, mil-spec carbon comp resistors, and a pair of NOS EF86 vacuum tubes.” The CT110HN (High Nickel) input transformers feature an extended high and low end and lots of headroom. The optional CT110 input transformers offer less headroom and extension but saturate easier while pushing more of the upper midrange. I tried both options in the review period and preferred the CT110.

Home on the Range

The Coils excelled across a range of applications but you have to plan ahead if you’re using condenser or active ribbon mics. Where phantom power was needed I used an ATUS CP8508 outboard phantom power supply. “We seriously contemplated the phantom power situation,” says designer Jim Vollentine. “For us it seemed like it would be an afterthought that would be difficult to implement on the module properly. You need blocking capacitors to keep the DC off of the input transformer, or you have to redesign the transformer with an air gap, which can compromise its sound. In all honesty, I tend to advise most of my engineer friends to use an external 48V box to keep from accidentally frying ribbon mics. Plus, good 48V makes your condenser mics sound better.”

I started with the CT110 input transformers and used the Coil to record a vintage 22-inch Gretsch round badge Blue Sparkle kick drum using an AKG D12 VR and the reissue of the Neumann U 47 FET. The D12 VR was placed right at the hole at the outside head and the U 47 FET was placed three inches back from the outside head. The D12 VR’s internal EQ was set to the third position, which boosted the lows, cut the woof at 400 Hz and boosted the attack of the beater around 5 kHz. The U 47 FET had both pads engaged. For transient material, I set the CA-286 input to 12 and output about 1 o’clock. I kicked back the NF dial to 9 o’clock, which makes the Hi and Low settings more active because they are in the negative feedback loop. I set the Low of the D12 VR to 3 o’clock and the U 47’s to 12 o’clock. As with any preamp, how hard you hit the input greatly affects how well the low frequency speaks. I moved the input to zero with the output down, which killed the transient and bottom end. As I rolled back the input and boosted the output, you could hear the veil coming off the kick until it was rich in the bottom end, like the kick drum sound you’ve always dreamed of getting.

On another session where there were two setups on the same kit in the same day, I used Shadow Hills Gamma 8 Blackbird Edition preamps on the Kick in and Snare top mics, which were a D112 and Shure SM57 mics, respectively. Not liking what we got in the morning, I switched from the Gammas to the CA-286 on both mics and the difference was night and day. Placement was close to the same and may have made a slight difference but was not enough to explain the fullness that came out of the kick on the second session. That said, I love the Gamma 8s and use them all the time on drums. On this day and on this kit, however, these mics sounded better through the CA-286 preamps.

Next I used the Coils to capture Craviotto 13x9 and 16x16 Walnut toms. The mics were two U 47 FETs run through the CA-286s, then to the line inputs of the Neve 8078 console on the way to Pro Tools in Studio A at Blackbird Studio. EQ on the high tom was a simple boost at 3.9 kHz to bring out the stick hit. The low tom called for some help at 100 Hz, a cut at 470 Hz to help with clarity, and a boost at 4.7 kHz for the stick hit. The CA-286 was moderately gained at the input, and the output adjusted to satisfy our level needs in Pro Tools. Like all dual gain devices, from guitar amps to preamps, setting the input moderately and gassing the output will give you the cleanest possible signal. On a suggestion from Vollentine, I played with the NF knob, turning it clockwise to reduce cymbal bleed. Vollentine says: “That crazy knob changes the reach/sensitivity of your microphones by ‘dampening’ the circuit…” I had the drummer play his ride cymbal while he hit the high tom to see what the knob would bring to the game. As much as I’d like to say it’s earthshaking, I couldn’t hear the benefit. That’s not to say I didn’t love what I already had, which was stellar.

The CA-286 sounded great on electric guitar played through a Fender Deluxe amp. For this application I switched the input transformers to the C110HN versions. The mics were a Neumann U 87 and an AEA N22 active ribbon microphone. Both mics were gained at 19 on the input and the output was set about 10 o’clock. The sound was clean, bright and beautiful. This time the NF knob had a larger effect most likely due to the more complex harmonic content. Turning it clockwise and back again added some richer tone in the lower midrange. The Hi and Low knobs had little effect no matter where the NF knob was set. I was really hoping to hear the effect of these knobs and made every effort to let them show their stuff to no avail.

I then used the CA-286 to record a bass through a Fender Vibrolux amp at low volume. The Fender P-Bass was recorded direct through a Countryman DI, then to a Neve 8078 console preamp (1073), adding a few dB at 100 Hz, then directly to Pro Tools. At the same time, I used an AEA N22 and Royer 121 on the Vibrolux, then to the Coil preamps. The N22 required the OB phantom power box mentioned earlier. The artist used a bit of spring reverb in the bass sound for some extra flavor. The combination of the three tracks was thunderous. The DI was clean and had all the delicious Class-A richness the 1073 offered. The N22 had more top than the Royer but also supplied some great bottom end. The 122 through the Coil brought a subharmonic that surprised everyone in the room. I had switched back to the 50/ 50 nickel input transformers, which I preferred throughout the review. The NF dials were at their fully counter-clockwise position, which filled out the bottom end nicely. Once again, even after polling all the ears in the room, I could hear no difference in the sound when the Hi and Low knobs were moved throughout their full range.

A Pleasure To Use

The CA-286 is truly a modular system that can be purchased as a single unit, or up to a 6-channel version in a single (albeit very tall) rack. The multi-unit rack is purchased separately and comes with a beefy, external power supply. Prices for the PS-6 rack, which holds up to six preamps, is $990. Each CA-286 preamp to fit this configuration is $1,500. The CA-286 PS2 Stereo unit tested here is $3,500 and uses an integral power supply. All have the same controls and swappable transformers mentioned above.

The Coil was a pleasure to use wherever it was applied, bringing rich tone and surprising harmonic content to a variety of instruments. It excelled on electric guitars, electric bass and drums. My only wish is that I had more space here to talk about all the other applications where it rocked, including across the stereo bus in line level mode, on vocals, and used with other mics on toms and percussion. If you’re looking for a great preamp that will stand the test of time and certainly appreciate in value, this is your box. 

Kevin Becka is Mix’s technical editor.


Try This

Set the input from the fully left position (LN), and use the output gain to get the level you need to your DAW. Conversely, push the input hotter and bring back the output to play with all the sonic options that the tubes in the unit provide.


Product Summary

COMPANY: Coil Audio


WEBSITE: coilaudio.com

PRICE: $1,500 (starting price)

PROS: Fat, beautiful tone. Great fit, finish and attention to detail.

CONS: The effects of the Hi and Low knobs are too subtle to quantify.

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