Presonus Eureka mic preamp /channel strip

For sale...This Presonus Eureka mic preamp /channel strip is loaded with features and is good shape for a used piece of rack gear. VU meter works fine but illumination light is out. All other functions and controls are perfect. Very quiet and plenty of gain. Variable input impedence is really nice for users of ribbon mics ! Compressor and EQ sections are very efective and musical sounding. This is the perfect mic pre if you are looking for a clear , colorless transparent sound.

Construction is very sturdy; pots have smooth operation and detents for repeatable settings.

FEATURES:
• Class A High Headroom Transformer Coupled Microphone Preamplifier
• Variable Microphone Input Impedance
• Variable SATURATE control (simulates tape saturation and tube warmth)
• Fully Variable Compressor with Hi-pass Side Chain
• Three Band Fully Parametric Equalizer
• EQ Pre or Post Compressor
• High Headroom Output Section
• Very Low Noise Design
• Internal Power Supply
• Transparent, wide range performance
• Optional 24-Bit/192k Digital Output Card (AD192)
SPECIFICATIONS:

Channels One Dynamic Range >115dB Headroom +22dB Frequency Response 10Hz to 50kHz Internal Operating Level 0dBu = 0B
Microphone Preamp   Input Impedance, XLR Input 1.3k Ohms Input Impedance, Line Level Input 10k Ohms Connectors Neutrik™ Combo
Microphone Preamp   Gain +12dB to +52dB Noise Floor -112dBu (+12dB gain) EIN -127dB THD + Noise (0% saturation) <0.005% THD + Noise (full saturation) <0.5% Microphone Input Connector XLR Microphone Input Impedance (selectable) 2.5k, 1.5k, 600, 150, 50 Ohms Instrument Input Connector 1/4" TS Instrument Input Impedance 1 Meg Ohm Send Connector 1/4" TRS balanced/unbalanced Send Output Impedance 51 Ohms Return Connector 1/4" TRS balanced/unbalanced Return Input Impedance 10k Ohms Metering (3-LED) -20dBu, 0dBu, Clip Line Input (switchable) 1/4" TRS, 10k Ohm Input Impedance Phantom Power (switchable) +48V (pin 1, pin 2 XLR) Pad (switchable) 0dB/-20dB Phase (switchable) 0, 180 degrees Hi-pass filter (switchable) -3dB shelf at 80Hz
Compressor   Threshold (variable) -40dBu to +20dBu Ratio (variable) 1-10 (1:1 to 2:1) Attack (variable) 0.1 to 200 ms Release (variable) 0.05 ms to 3 S Gain Make-up -20dB to +20 dB Hi-pass Side Chain Filter (variable) 10Hz to 10kHz Metering Analog VU (gain reduction / Output Level)
Equalizer   Low Band (+/-13dB) 20Hz to 300Hz Mid Band (+/-13dB) 200Hz to 3kHz High Band (+/-13dB) 2kHz to 20kHz Q (variable all bands) Q=0.4 to 2 (3 octave to 2/3 octave)
Master   Output Fader -70dB to +10dB Output Connectors XLR balanced and 1/4" TRS balanced/unbalanced Output Impedance 51 Oms Metering (output level) Analog VU (-20dBu to +6dBu) Meter (gain reduction) Analog VU (-20dB to 0dB) Output Headroom +22dBu
Physical   Power Supply Internally Regulated Linear Type Power Requirements (factory configured) 120VAC Size 1U Rack Dimensions 19" x 1.75" x 7" Weight 8lbs.

This unit has enjoyed very favorible reviews, here is an excellent example with some very accurate observations both positive and otherwise...

Presonus Eureka
      Recording Channel
      Published in SOS May 2004
             
      This smart new unit offers EQ and compression, plus a transformer-coupled
      Class-A preamp and an unusual Saturation control.
      

     .
      The American manufacturer Presonus have produced a wide variety of
      cost-effective but always well-designed preamps and channel units. Many
      have been valve-based designs, but there have also been several
      solid-state devices. One such product was the VXP reviewed by Paul White
      in SOS March 2001, and the Eureka under review here bears some striking
      similarities to that unit (although at a significantly lower UK price).
      Most notable is the porting across of several key technologies, including
      the transformer-coupled Class-A preamp and the unusual and adjustable
      saturation distortion control. This bestows the Eureka with a sound
      character between a traditional valve-based preamp and a solid-state one.
     

 Facilities Overview
      The facilities provided by the Eureka are fairly conventional for a mono
      channel strip. There's a switchable mic, line and DI input, a flexible
      solid-state compressor, and a three-band, fully-parametric EQ. There is
      also a balanced insert point immediately after the preamp section, and the
      equaliser can be switched into circuit either before or after the
      compressor.
      As already mentioned, the mic input is transformer balanced and features a
      discrete Class-A FET buffer followed by a 'dual servo' gain stage using
      industry-standard NE5534 op amps. The FET buffer circuitry incorporates
      the unusual Saturation facility (created by varying the FET drain current)
      which generates an adjustable degree of even-order harmonic distortion.
      This provides a variable quasi-valve warmth, yet with the benefit of
      solid-state precision and reliability. Another facility included in this
      preamp design — and one which is becoming increasingly popular — is a
      variable input impedance, spanning 50-2500(omega) in this case. A simple
      three-LED input meter is provided, showing -20dBu, 0dBu, and clipping
      (+22dBu). Although better than nothing, I felt that this input metering
      was a little too simple to be very useful.
      The compressor section is based around the familiar THAT 4301 VCA chip,
      and includes a complete set of user controls rather than the preset modes
      offered in the VXP. A variable high-pass filter is also included in the
      side-chain to enable simple frequency-dependent dynamic processing — such
      as crude de-essing — and the compression characteristic can be switched
      from the default hard knee to a soft-knee mode, enabling both dramatic and
      more subtle compression effects.
      The three-band parametric equaliser section is versatile, and avoids the
      dual-concentric controls that Paul found frustrating in the VXP, although
      the close proximity of controls still makes it fiddly to adjust for anyone
      with fingers thicker than a supermodel's. The band gain controls provide a
      slightly smaller boost and cut gain range than most designs, with just
      10dB on offer, but there's usually something seriously wrong if you need
      more than that from a general-purpose analogue equaliser! The side effect
      of a restricted control range is that the precision of gain setting has
      been usefully enhanced.
      The bandwidth of all three sections can be varied from a narrow two thirds
      of an octave (Q value of two), to a broad two octaves (Q value of 0.4),
      and with the widest bandwidth settings and extreme frequency positions the
      top and bottom bands can be made to serve as reasonable shelf filters too.
      The frequency ranges of all three bands overlap well to provide seamless
      coverage of the entire spectrum.
      The electronically balanced main output is provided on both XLR and TRS
      sockets, and the nominal level can be controlled between +10dBu and about
      -80dBu. A small moving-coil VU meter in the centre of the front panel can
      be switched to show either the output level or the compressor's gain
      reduction. The insert point is fully balanced, with separate TRS sockets
      for send and return.
      An optional 24-bit A-D module can also be installed via the rear panel if
      required, operating at all the standard sample rates from 44.1kHz to
      192kHz, and providing both AES-EBU and S/PDIF outputs. Since these are
      both dual-channel interfaces, an auxiliary balanced TRS socket accepts an
      external analogue line-level signal to access the second A-D channel — the
      Eureka's own output signal occupying the first digital channel.
      Unfortunately, this A-D converter module was not provided for the review,
      so I am unable to comment on its performance.

      Internal Circuitry
      The Eureka is certainly well built. The majority of electronics are
      contained on a main PCB which covers most of the available floor area of
      the box, with mic preamp circuitry to the left, dynamics and EQ in the
      centre, and an integral linear power supply to the right. Three power-rail
      regulator chips are mounted on a metal strip running from front to back
      inside the unit, and this acts as the only heat sink — but the power
      consumption is very small so heat isn't really an issue. The main circuit
      board has a rectangular section cut away in the centre at the rear to
      accommodate the optional A-D converter module. This can be fitted by the
      user very easily, as it is simply bolted in place and connected to the
      main unit via a small multi-pin plug.
      Most components on the circuit board are surfacemount devices, although
      there are a few conventional-sized components too, including a pair of
      socketed NE5534 op amps in the input stage. Two small daughterboards run
      just below the lid to carry and the top row of front-panel switches and
      controls, while the toroidal mains transformer and mu-metal screened mic
      transformer are located at opposite sides of the box. One point worth
      noting is that the mains operating voltage is factory configured and not
      user adjustable. The IEC mains inlet incorporates a fuse holder accessible
      from the outside, and the mains power switch is also located here on the
      rear panel — which may be a blessing or a hindrance depending on your
      point of view!
     

      Front-panel Layout
     

      The Eureka looks very clean and tidy, with lots of small blue knurled
      knobs on a brushed-steel front panel. The panel markings are small but
      clearly legible, and all of the continuous rotary controls have a light
      detented action traversing about 40 'clicks', which gives good tactile
      feedback. Unfortunately, though, this detented action feels rather more
      precise than it really is, and doesn't help in locating the unity
      positions of the gain controls, for example. So, to set the output level
      to the calibrated unity gain mark, or to cancel the gain of an EQ section,
      you are forced to look closely at the panel markings, instead of just
      feeling for a centre detent. It's a small point, but one which some users
      might find frustrating after using the unit for a while — I know I did!
             
      The input stage is easy and logical to use, with three rotary controls
      along the bottom and five illuminated buttons running in a row above.
      Microphone input gain is continuously adjustable from +10dB to +54dB, but
      this can be supplemented by an additional 10dB of make-up gain in the
      compressor and a further 10dB at the output level control, giving a
      maximum overall gain of 74dB. The microphone preamp is specified with an
      EIN value of -127dB (weighting not given) and distortion is quoted as
      below 0.005 percent with no saturation (rising to 0.5 percent with full
      saturation).
      The buttons provide phantom power, a 20dB pad, an 80Hz high-pass filter,
      and polarity reversal. One of the other two rotary controls adjusts the
      Saturation from zero to 100 percent, and increasing the Saturation
      certainly adds a warmer character to the sound, making it sound thicker
      and richer. However, this is pretty subtle most of the time, and it's not
      quite of the same character as the distortion you get in a typical valve
      preamp. Then again, it isn't as unpredictable as valve preamps, and won't
      wear out either! I'm sure many users will find it a very useful facility,
      but don't audition the Eureka with the expectation of it sounding like a
      traditional valve preamp.
      The third rotary control is actually a switch to change the input
      impedance in five steps from 50(omega) to 2500(omega). Many preamps
      offering variable input impedance provide a higher maximum figure than
      this — typically 5k(omega) or so — but the range offered here is
      sufficient to match a wide selection of mics, including most ribbons, and
      affords useful tone-shaping characteristics which are far more subtle than
      most EQs can manage.
      The fifth and final button selects the fixed-level line input, which
      bypasses the mic input stage altogether and so is unaffected by the Gain,
      Saturation, and Impedance controls. The front-panel unbalanced instrument
      input presents a 1M(omega) input impedance and is selected automatically
      when a plug is inserted. The DI input is processed through the microphone
      gain stage (with a lower overall gain spanning 0-44dB), and is therefore
      able to take advantage of the Saturation effect, which is a nice facility.
      In fact, the DI input sounds particularly good, with a full rich character
      — I find many preamp DI inputs tend to sound rather too clean, but not the
      Eureka. I'd still recommend recording guitars and basses through a decent
      simulation system like the Pod XT, but if you want a simple clean input
      then this is a good one.
     

      EQ & Dynamics 

      The front panel places the dynamics control section before the equaliser,
      and the default signal path follows the same order, but an illuminated
      button allows that sequence to be reversed should you need to equalise
      before compressing. The compressor is fully featured, with six rotary
      controls and a pair of illuminated buttons. The Threshold control spans
      +20dBu to -40dBu, enabling the compressor to be used effectively as a peak
      limiter at high threshold values and ratios. The Ratio control is scaled
      rather oddly from zero to 10, but actually offers a range of 1:1 up to
      2:1, and has a hard-knee response by default. A soft-knee curve can be
      switched in when a more subtle effect is required. The Gain control offers
      a ±10dB range, and the Attack and Release controls are both marked simply
      with Fast and Slow at their control extremes. However, the attack-time
      range is detailed in the specifications as being adjustable from 0.1ms to
      200ms, while the release-time covers 0.05s to 3s.
      The last rotary control determines the turnover frequency of the
      side-chain's high-pass filter. This is adjustable from 10Hz to 10kHz, and
      is useful for reducing the compressor's sensitivity to bass instruments at
      the lower end of the scale, and for helping the compressor react only to
      sibilance at the higher end of the scale. The entire compressor can be
      bypassed by another button, and the amount of gain reduction can be
      displayed on the central VU meter.

      The equaliser occupies most of the panel space to the right of the VU
      window, with three sets of three rotary controls plus another pair of
      illuminated buttons. The first button places the EQ before the compressor,
      as described above, and the second bypasses the entire equaliser circuit.
      The controls in all three bands follow the same order left to right — Q
      (bandwidth) followed by Gain then Frequency — but the middle section is
      reversed vertically compared with the outside two. In other words, the
      Gain control is above the Q and Frequency controls for the centre section,
      but below for the other two. This caused some operational confusion
      initially, but once familiar with the unit I found it fairly easy to
      navigate the controls. I have already mentioned the ranges afforded by the
      Gain and Q controls, so to complete the picture the frequencies covered by
      each band are 20-300Hz, 200-3000Hz, and 2-20kHz respectively.
      As you would expect, the equaliser section is versatile and sounded pretty
      good to my ears — far better than the average budget mixing console's EQ,
      and capable of better high-frequency correction than most software
      plug-ins. The ability to vary the Q over a reasonably wide range is
      certainly helpful when trying to tune in to a specific part of the
      spectrum, allowing each EQ section to affect a broad range for gentle
      tonal shaping, or a narrow range for more delicate corrective surgery.
      The final control panel section is the output stage, with the output fader
      and a button to switch the VU meter between output and gain-reduction
      levels. The output can sustain signals up to +22dBu from a low 51(omega)
      source impedance, which is the same as the balanced insert send point. The
      balanced insert return and line input both share a 10k(omega) impedance
      and can accommodate signals to +22dBu.
      

       Verdict
      

      The Presonus Eureka doesn't have the larger-than-life low-frequency
      quality associated with true high-end preamps, but it remains well
      controlled at the bottom with a detailed top end and a neutral overall
      balance. I would liken the Eureka's preamp stage to that of a
      good-quality, traditional mixing console — there's something about a
      transformer input stage that just sounds right. The Eureka offers a
      worthwhile step up in quality from the relatively simple mic input stages
      of budget mixers and computer interfaces.
      The Saturation control can be used to smooth any hard edges from the top
      end, while adding an extra richness and density through the mid-range.
      With most sources — such as vocals and some instrumental sources like
      electric or electronic keyboard parts — the subtle distortion sounds
      musically flattering. However, it's not an effect to overuse: the addition
      of those extra harmonics not only thickens the sound, but also tends to
      obscure transient detail, so it can be damaging on complex and delicate
      sources — such as acoustic guitars (especially 12-strings) or crisp
      percussion parts. Overall, the Eureka is a very good-sounding unit —
      especially given the UK price — and easily stands up to comparison with
      higher-priced channel strips from the other major players in this field. 
     

      Quoted from SOS May 2004