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PreSonus Eureka PreAmp Signal Processor

Regular price $279.00

The Great Discovery

The name “Eureka” derives from a Greek word meaning “I have found it!” It was made famous by the ancient Greek scholar Archimedes, indicating exultation at a great discovery. Try the sweet-sounding, super-versatile Eureka preamp and signal processor, and you’ll discover the answer to a variety of sonic needs.

One of our best-selling products, the Eureka is equally at home in the studio or at the gig. With separate mic, line, and instrument inputs, you can employ it on almost any sound source.

Sweetening starts with a high-headroom Class A solid-state mic preamplifier with +22 dBu of headroom, providing wide dynamic range and excellent transient-response characteristics.

Power amplifiers are classified primarily by the design of the output stage and are designated Class A, B, AB, D, G, or H. In a Class A preamp, the output circuits are always on for the entire cycle of signal swing or the bias current flows at all times.

As a result, Class A preamps have the most linear design, with no crossover distortion, and they deliver purer, clearer, and more musical results than the Class AB designs that are found in many preamps.

Eureka contains a Class A discrete input buffer followed by a dual-servo gain stage. This yields ultra-low noise and wide gain control, allowing you to boost desirable signal without increasing unwanted background noise.


The preamp’s variable mic-input impedance enables you to vary the “color” of your sound and get the best performance from any type of microphone.

Most mic preamps have a fixed microphone-input impedance of between 1 and 2 kΩ. The Eureka provides variable microphone-input impedance, which can be set at 50Ω, 150Ω, 600Ω, 1.5 kΩ, or 2.5 kΩ.

As the impedance is lowered, a resistive load is put on the microphone. This will not damage the microphone but lowering or raising the impedance can create subtle coloring and filtering effects, enabling you to get a wider variety of sounds.

In general, a lower input impedance can add color to the mic to produce effects that simulate a “darker,” or more “closed-in” tone, or that change the mic’s apparent sensitivity. This effect is easier to notice on passive microphones (ribbon or moving coil) than on active microphones (condensers or active ribbons/dynamics).

In addition, some microphones are finicky about impedance; with variable impedance, you can make virtually any mic deliver its best performance.



A Saturate control simulates the effects of tape saturation and tube warmth so you can go from crystal-clear to warm and rich.

The Eureka employs a high-quality transformer and features a Saturation control that adjusts the drain current on the input FET amplifier, altering the levels of even harmonics in the signal being passed. The Saturation control offers an adjustment range of 0% to 100%. The 0% position passes a pure signal. As the control is rotated to the 100% position, the signal’s even harmonics are boosted, giving the signal “warmth” very much like a vacuum tube or similar to the sound of analog-tape saturation.



Go with the Flow

The Eureka’s versatility stems in part from its malleable signal flow. With both XLR and ¼” line outputs, you can connect the Eureka to almost any recording interface, amp, or P.A. system. The EQ can be pre- or post-compressor, and you can bypass each independently. Balanced send and return jacks enable you to insert your favorite outboard processor before the compressor and EQ.

The backlit VU meter can display gain reduction or output gain.

Compression, EQ, and More

The channel strip’s fast, fully variable compressor provides Attack, Release, and Ratio controls and can be switched between hard and soft knee. 

The term “knee” refers to the way the compression curve bends at the threshold point when represented graphically.

With hard-knee compression, the gain reduction applied to the signal occurs as soon as the signal exceeds the level set by the threshold.

With soft-knee compression, the onset of gain reduction occurs gradually after the signal has exceeded the threshold, producing a more musical response (to some folks).


The compressor includes an internal sidechain with variable (10 Hz to 10 kHz) high-pass filter, so it can achieve anything from hard pumping to transparent compression.

Sidechaining is useful for numerous applications, including removing sibilance from vocal tracks (de-essing), spectral processing, compression keying, and automatically ducking (lowering the level of) music tracks behind a narrator in a service, broadcast, or performance.

Sidechaining is often used for frequency-dependent gating, in which you put an equalizer or filter before the gate to, say, cut only the lower frequencies of a kick drum. The Eureka’s compressor sidechain includes a dedicated, variable (10 Hz to 10 kHz) high-pass filter for this purpose.


The Eureka’s three-band, fully parametric EQ has overlapping frequency selection on each band. It can be used pre- or post-compressor and can be bypassed.

The Eureka provides a fully parametric equalizer—that is, you0 can independently control each band’s center frequency, gain, and Q. The frequency of the low band can be varied from 20 to 300 Hz, the mid band from 200 Hz to 3 kHz, and the high band from 2 kHz to 20 kHz.

Q is defined as the ratio of the center frequency to the bandwidth; a lower Q results in a wider frequency band. The Q on the Eureka ranges from 0.4 (wide) to 2.0 (narrow). In octaves the Q on the Eureka ranges from 3 octaves to 2/3 octaves.


Of course the Eureka provides all of the secondary features you need in a preamp/channel strip.  A 20 dB pad lets you tame hot input signals, and a high-pass filter attenuates all frequencies below 80 Hz by 12 dB. Polarity reverse enables you to deal with phase problems when using open mics.

Try the Eureka. Like the great Archimedes, you’ll be shouting, “I have found the solution!”



Input Channels 1
Dynamic Range >115 dB
Headroom +22 dB
Frequency Response 10 Hz to 50 kHz

Microphone Preamp

Input Impedance, XLR Input 1.3 kΩ
Input Impedance, Line Level Input 10 kΩ
Connectors Neutrik™ Combo
Gain +12 dB to +52 dB
Noise Floor -112 dBu (+12 dB gain)
EIN -127 dB
THD + Noise (0% saturation) <0.005%
THD + Noise (full saturation) <0.5%
Microphone Input Connector XLR
Microphone Input Impedance (selectable) 50Ω, 150Ω, 600Ω, 1.5 kΩ, or 2.5 kΩ
Instrument Input Connector ¼” TS
Instrument Input Impedance 1 MΩ
Send Connector ¼” TRS balanced/unbalanced
Send Output Impedance 51Ω
Return Connector ¼” TRS balanced/unbalanced
Return Input Impedance 10 kΩ
Metering (3-LED) -20 dBu, 0 dBu, Clip
Line Input (switchable) ¼” TRS, 10 kΩ input impedance
Phantom Power (switchable) +48V
Pad (switchable) 0 dB/-20 dB
Phase (switchable) 0, 180 degrees
High-pass filter (switchable) -3 dB shelf at 80 Hz


Threshold (variable) -40 dBu to +20 dBu
Ratio (variable) 1-10 (1:1 to 7:1)
Attack (variable) 0.1 to 200 ms
Release (variable) 0.05 ms to 3 seconds
Makeup Gain -20 dB to +20 dB
High-pass Sidechain Filter (variable) 10 Hz to 10 kHz
Metering Analog VU (gain reduction / Output Level)


Low Band (±13 dB) 20 Hz to 300 Hz
Mid Band (±13 dB) 200 Hz to 3 kHz
High Band (±13 dB) 2 kHz to 20 kHz
Q (variable all bands) Q=0.4 to 2 (3 octave to 2/3 octave)


Output Fader -70 dB to +10 dB
Output Connectors XLR balanced and ¼” TRS balanced/unbalanced
Output Impedance 51Ω
Output-level Meter Analog VU (-20 dBu to +6 dBu)
Gain-reduction Meter Analog VU (-20 dB to 0 dB)
Output Headroom +22 dBu


Internal supply, standard IEC connector 100 VAC to 120 VAC, 200 VAC to 240 VAC


Dimensions 1U rackmount
Height 1.75” (44.45 mm)
Depth 7” (177.8 mm)
Width 19” (482.6 mm)
Weight 8 lbs. (3.63 kg)

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