by Steve Cunningham

PreSonus has been around for almost ten years, making moderately priced microphone preamplifiers as well as outboard EQ and compressors. I’d used a PreSonus eight-channel pre several years ago, and while it was good for the price it, didn’t have enough clean gain for low-output dynamic mics like the RE-20. Nevertheless, I was intrigued when PreSonus announced an optional 192 kHz AES output card for their Eureka mic processor, and I’d heard good things about the box from colleagues. So this month we’ll look at yet another entry in the low-cost “channel strip” category, the PreSonus Eureka.

The Eureka is a single channel microphone processor whose front panel is divided into four sections: Transformer Coupled Preamp, Compressor, Parametric Equalizer, and Master. With a street price under $500, the Eureka gives you a lot of features you wouldn’t expect, including variable impedance selection and transformer saturation. Moreover, the Eureka’s performance with dynamic mics has improved markedly compared to older products.

diagram large back eureka


The single-space Eureka’s face is machined from a single piece of brushed aluminum, which in turn is dense with anodized blue knobs and buttons lit with blue LEDs. Front and center is an old-school backlit analog VU meter that can display output level or gain reduction.

The rear panel has a single balanced mic input on XLR, and another balanced line input on a 1/4" TRS jack. The output section is identical, with one XLR output and one 1/4" TRS output, and both are active at all times. There are balanced TRS send and return jacks on the back as well, along with the IEC connector for the power cord and the on/off power switch. Having the power switch on the back panel could be an annoyance, depending on your studio setup, but it didn’t bother me.



As I mentioned, the front panel is dense, so we’ll take it by section. On the left side is the mic preamp, which is a transformer coupled solid-state Class A unit (yes, there’s a real transformer inside – I checked). The input meter consists of three blue LEDs, one each for -20dB, 0dB, and Clip, and they flash in increasing intensity with the input signal level. It’s a drag that there are only three LEDs, and that they’re all blue in color - you have to pay close attention to them to be sure you’re not clipping, and no, you can’t use the big VU meter to monitor the input level. The jack below the level LEDs is a TS connector for high-impedance instrument signals (input impedance is 1 Meg ohm). Plugging into this input bypasses the mic preamplifier and the Eureka becomes an active instrument preamp.

There are a total of five pushbuttons in the preamp section, each of which lights up when active (in LED blue, of course). The pushbutton labeled LINE selects the line input on the back as the input in use. When the Line input is in use, the microphone preamplifier stage is bypassed and thus the Gain, Impedance and Saturate controls are inactive. The other pushbuttons activate 48-volt phantom power, a 20 dB pad, a highpass filter set at 80 Hz, and a phase reverse switch.

On to the knobs, all of which on the Eureka are stepped pots (excepting IMPEDANCE which is a 5-position switch). The knob’s “steps” don’t seem calibrated to any particular values, and besides the legends around them are much too small to read anyway. But they do give the knobs a nice solid feel. For example, the GAIN knob ramps up smoothly to a full +54 dB of preamp boost, which was quite adequate for the problematic RE-20.

The IMPEDANCE knob allows you to select one of five different settings to match or intentionally mismatch the input impedance of the preamp to a particular microphone. The settings cover a broad range from 50 to 2500 ohms of impedance, and let you “tune” the preamp to a variety of microphones. It can also be used as a tone-shaping effect. The lowest setting, 50 ohms, should be great for most ribbon mics. Used with condensers, reducing impedance cuts low end and results in lower output. Fortunately, Eureka has more than enough gain to make up for that. For most applications, you’ll use the 2,500-ohm impedance, but the tonal options provided by the other settings are a nice bonus. The RE-20 seemed happiest at 600 ohms, a good compromise between low end and sensitivity. This one I like.

The SATURATE knob however, is somewhat inscrutable. PreSonus says this feature adds “warmth” and increases the even harmonics of the input signal to simulate a tube, and works by manipulating the drain current of the FET input buffer of the preamp. It adds something for sure, but I’m not sure I’d call it “warmth.” It sounds to me like it scoops out the upper midrange, and at maximum level it muffles the sound. Nope, this one I don’t like much.

Having said that, the preamp itself is very good. It has lots of clean gain, almost no self-noise, and almost no coloration. It can get a little harsh on sibilance, but there’s a de-esser in the compression section as we’ll see.

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