Electronic Musician''s review of the PreSonus Eureka, a single-channel preamplfier, compressor, and equalizer.

The Eureka is a formidable new channel-strip processor from PreSonus that features a mic preamp, a compressor, and a 3band parametric equalizer. With a list price of $699, it falls in the low- to midprice range, an area in which PreSonus has previously succeeded with products such as the MP20 mic preamp and the BlueMax compressor.

PreSonus is also releasing the AD192, an optional 24-bit, 192 kHz digital-output card ($249) that goes with Eureka and will make the unit even friendlier for DAW applications. The card wasn't ready to ship at the time of this writing, but according to PreSonus, it should be available by the time you read this.


The Eureka looks bold and elegant, with a brushed steel face and cobalt metal knobs (see Fig. 1). Its switches light up a nice, eerie blue when engaged, making it easy to see their respective states at a glance. Trying to see the knob settings is not as easy; they reflect so much light that it's difficult to see their indicator lines. (Ironically, it was only in low light, with the unit angled in a particular way, that I could easily see the settings. In a rack, with normal lighting, it was almost impossible.)

As you would expect, most of the inputs and outputs are on the back panel, but for convenience, there is a ¼inch instrument input on the front. Above it are three LEDs (showing -20 dB, 0 dB, or Clip) that indicate signal strength at the instrument and mic inputs. The input section's three knobs control preamp gain, impedance, and saturation (which I'll discuss more later). Above these knobs are switches for activating the line input, the +48V phantom power, the -20 dB pad, the 80 Hz highpass filter, and the polarity-reverse function.

The Compressor section offers a comprehensive set of controls: Thresh (threshold), Ratio, (makeup) Gain, Attack, Release, and Sidechain Hi Pass, a filter control for frequency-dependent compression applications such as de-essing. You can tailor the compression further with the Soft switch, which toggles between soft- and hard-knee compression curves. Finally, there's a Bypass switch for taking the compressor out of the circuit. The default, unlit state of the switch indicates that the circuit is active, which may be counterintuitive to some users.

In the middle of the Eureka's front panel is a brightly lit VU meter with the PreSonus squiggle logo printed on it. For engineers who are used to looking at analog tape machines, the VU meter is an especially nice feature, even if it adds slightly to the cost to the unit.


To the right of the meter is a 3band, fully parametric EQ. Each band has three knobs: Q (bandwidth), Gain, and Freq (center frequency). For each band, the range of the Q is from three octaves to two thirds of an octave, getting narrower as you turn the knob clockwise. The Gain knob allows up to 10 dB of boost or cut for each band.

The frequency range of the EQ is 20 Hz to 20 kHz, divided among the bands as follows: the Low band ranges from 20 Hz to 300 Hz, the Mid band from 200 Hz to 3 kHz, and the High band from 2 kHz to 20 kHz. The EQ circuit has its own bypass switch and a switch labeled EQ>Cmp that places it before the compressor in the audio signal path, which is a very handy feature.

To accommodate the many controls in the EQ and compressor sections, PreSonus staggered the knobs for each in a zigzag fashion. As a result, I found the knobs to be a little too close together to adjust comfortably. That said, the knobs do have a solid feel and nice turning action, and they are detented in steps, which is useful both for recalling settings and for making fine adjustments. Rounding out the front panel are a master volume knob, with a range of -80 dB to +10 dB, and a switch for assigning the VU meter to the task of showing the compressor circuit's gain reduction instead of output level.

Eureka's back panel (see Fig. 2) features an XLR mic input, a ¼-inch TRS line input, separate balanced ¼-inch TRS send and return insert jacks, and both XLR and ¼-inch TRS jacks for the line-level output.


I tried the Eureka in a variety of tracking and overdubbing applications, and I compared it to other preamps in my rack, including the Focusrite ISA 428 PrePack (my current benchmark pre), the Focusrite Platinum VoiceMaster (a “channel-strip” box in the same price range as the Eureka), and PreSonus's own MP20 dual mic pre. I was surprised at how well the Eureka held its own.

The Eureka reportedly has a similar preamp design to the MP20, which I've used and loved for years: a discrete Class-A, transformer-coupled, dual-servo, twin-JFET preamplifier. The only difference is that the Eureka's input impedance is selectable, whereas the MP20's is fixed at 1.3 kž. This added feature lets you match (or mismatch) the output impedance of the mic you are using, giving you additional control for tonal characteristics.

I question PreSonus's choice of 50ž as its lowest setting, however. That setting was completely unusable with every mic I tried, producing an extremely low and distorted output. The lowest setting on my other selectable-impedance preamp, the ISA 428, is 600ž, which seems far more useful as a low extreme. Conventional wisdom says the input impedance should run about ten times a mic's output impedance. Most common mics have impedances between 50 and 300ž, so it makes sense that a 50ž input impedance might not sound so good, except as a special effect.

The Saturate control (called IDSS on the MP20) emulates the effect that tape saturation and tube warmth have on the even-order harmonics of a sound. I never touch this knob on my MP20; doing so tends to dull the unit's otherwise sparkly tone without any sonic benefit. But the Eureka's Saturate control is useful, smoothing the grit on electric bass, distorted guitar, and gruff male vocals.


I began my testing by comparing the Eureka against my other preamps for recording direct electric bass. The Eureka sounded better than both the MP20 and the Focusrite ISA 428 for this application. I was quite surprised, considering that the ISA 428 blew me away the first time I heard it used for direct bass. The Eureka was rounder, fuller in the low end, and smoother in the highs than the ISA 428. The MP20 sounded slightly flat in comparison to the Eureka. The Focusrite Platinum VoiceMaster doesn't have an instrument jack, so I didn't include it in the direct-bass comparison.

I also tried running the electric bass through a bass amp, miking the amp with an AKG C 414 EB, and patching the mic's output through the various preamps. In this test, the ISA 428 one-upped the Eureka. The Eureka sounded best at the 2.5 kž setting, but the ISA 428 on its High Impedance setting (a much higher 6.8 kž) was clearer and crisper. Both the MP20 and the VoiceMaster were a little dull in comparison, which makes sense given the higher input impedance of the Eureka. Adding a little of the Eureka's saturation effect, which helped to smooth out the fret noise, sounded good in this instance.

Next I ran clean electric guitar through an amp, miked it with a Shure SM57, and ran its output through each of the preamps. The differences between the preamps were so subtle that there was no way to pick a clear winner. Again, the Eureka sounded best when I used its 2.5 kž impedance setting. With clean guitar, I found that dialing in any of the saturation effect destroyed the sparkle in an unpleasant, muffling way.

On distorted guitar, the Saturate knob pleasantly smoothed out the grit. It might make the guitar seem a little dark in a mix, but on its own it rounded out the otherwise harsh sound. The ISA 428 also excelled in this test, but the Eureka sounded clearer and fuller than the MP20 and the VoiceMaster.

On male vocals, the ISA 428 had the greatest detail in both frequency and dynamics, but the Eureka (at 2.5 kž) and the MP20 were right behind, followed closely by the VoiceMaster.


I compaed the Eureka's compressor with a dbx 266A and various software-compression plug-ins for Digidesign Pro Tools and MOTU Digital Performer. The Eureka's line input makes it possible to use the compressor and EQ sections during mixdown. The line input and outputs are rated at 0 dBu = 0 dB, so theoretically a +4 dBu signal will be too hot coming in, and a -10 dBV signal will be a little too quiet. In practice a -10 signal drove the compressor and EQ perfectly well, but a +4 signal distorted the Eureka a little at the input stage. The unit's output was fine for both +4 and -10 inputs, but setting the input of my sound card to -10 resulted in a slightly better signal-to-noise ratio.

The Eureka's compressor was a bit more subtle than either the dbx or the plug-ins, even when pushed to its max. It seems better for gentle, musical compression than for extreme effect-type limiting. The controls are responsive yet gradual, and the included sidechain highpass filter is handy for de-essing or letting through low frequencies on drum overheads or bass tracks. The presets listed at the end of the manual offer good starting points for setting the compressor for various instruments.

As mentioned, you can monitor the gain reduction of the compressor on the VU meter, which is a capability usually found only on high-end units. Confusingly, however, the meter shows gain reduction even when the compressor is not engaged.

Also, when the compressor or EQ was switched in or out of the circuit, the unit emitted a loud pop. I realize that it's difficult to take components in and out of the signal path without some sort of click or pop, but it seemed louder on the Eureka than on other units I've worked with. (According to PreSonus, this was a problem found only on very early production units, and it has subsequently been remedied.)

That aside, the EQ circuit, like the compressor, was user-friendly and musical. It was slightly subtler and more transparent than the EQs in my DAWs and on my console, but that's generally a good thing. The inclusion of three bands of fully parametric EQ is quite remarkable for this price range, as is the smoothness of the high band.


I was quite impressed with the Eureka. For tracking and mixing, it offers a winning combination of versatility, control, and excellent sound quality that's sure to appeal to seasoned engineers and less experienced recordists alike.

Eli Crewsis an Oakland-based engineer and musician. For information on Eli and his studio, go



channel strip


PROS: Good sound quality. Separate, balanced send and return insert jacks. Selectable mic input impedance. VU meter that can show gain reduction. Natural-sounding compression. Good-sounding EQ offers three fully parametric bands.

CONS: Knobs are small and close together. Knobs' shiny surface makes it hard to see indicator. Lowest impedance setting too low for most uses.


PreSonus Audio Electronics
tel. (800) 750-0323 or (225) 216-7887

Eureka Specifications Channels 1 Audio Inputs (1) balanced XLR mic; (1) ¼" balanced TRS line; (1) ¼" TS inst.; (1) ¼" balanced/unbalanced TRS insert send Audio Outputs (1) XLR; (1) ¼" TRS; (1) ¼" balanced/unbalanced TRS insert return Input Impedance 2.5 kž, 1.5 kž, 600ž, 150ž, or 50ž (mic, selectable); 10 kž (line/insert return); 1 Mž (inst.) Output Impedance 51ž Dynamic Range >115 dB Headroom +22 dBu Frequency Response 10 Hz to 50 kHz Gain +12 dB to +52 dB Total Harmonic Distortion <0.005% (no saturation); <0.5% (full saturation) Dimensions 19.00" (W) × 1.75" (H) × 7.00" (D) Weight 8 lb.