Microphone Preamplifier System

FEATURES

ORDERING

SPECS

USER GUIDE


BENEFITS
  • Extremely high resolution, low coloration
     
  • Combines wide dynamic range with wide bandwidth and both over the entire gain range, not just a "sweet spot"
     
  • High compliance input/output - high performance with a wide variety of input sources and output loads
     
  • Robust design and build

HIGHLIGHTS

  • True variable gain - no excess gain, no attenuators, no loop feedback
     
  • Output load compensation for low distortion output into any load

FEATURES

  • Overload-proof input clips after the output and without pads
     
  • Separate gain control with peak indicator, mute, and phase invert
     
  • Remote control eliminates cable losses and interference by locating the preamplifier near the microphone or instrument
     
  • Low noise, high gain (and, with remote, short mic cables) for optimal performance with ribbon microphones

Signal path

  • Balanced, high-impedance input thru parallel 1/4" and XLR connectors with switchable input impedance accepts mic, line or DI sources
     

  • Two megohm input impedance eliminates current-related losses and load distortion in mics
     

  • Balanced, symmetrical, discrete topology from input to output no transformers, no op amps
     
  • FET gain and direct-coupled output stages with auto-bias
     
  • Select point-to-point wiring
     
  • Non-magnetic enclosure
     
  • Extremely high input-output Z ratio for other applications including phono preamp, headphone amp, and line/buffer amp

Support functions

  • Local, discrete voltage regulation for each channel
     
  • Standby mute function enabled during power-up sequence, low line, and phantom on/off
     
  • Status indicator shows operation of gain control, output stage, and standby mute
     
  • Shielded internal primary supply with low leakage current

Mechanical

  • No steel rugged, anodized aluminum enclosure and stainless steel fastening hardware
     
  • Removable rack kit and optional outriggers for freestanding applications
     
  • Gold-plated contacts and active retention in all internal connectors
      
  • Fully enclosed, gold-plated contacts in panel switches and relays
      
  • Low-profile buttons and solid aluminum knobs with two set screws on " metal shafts no toggle switch bats, plastic knobs or terminal strips to break
     
  • Protected panel graphics are printed on the back of clear overlays


Combo 1.jpg (886668 bytes)

A standard XLR cable links the GC34 gain control (top) to the Model 4 single-channel preamp (center) or Model 5 dual-channel preamp (bottom).  The Model 4 also includes onboard controls.


SOFT SIGNAL PATH

     Preamplifier design concepts have not changed much since the advent of electronic amplification. Fixed elements (gain and buffer stages) and variable elements (attenuators or feedback) are arranged in a fixed signal path. Signal is amplified far more than is required, attenuated to the desired level, and buffered at the output with little regard for the load.

     Gordon Instruments has developed a "soft signal path" concept where each stage and the path itself are variable, optimized automatically for the selected gain and the output load. This innovation has been incorporated into the Gordon Microphone Preamplifier System along with high-resolution analog design, component, and assembly technologies, forming a very powerful sonic combination.


TRUE VARIABLE GAIN

     The primary source of distortion in any preamplifier is gain. In conventional microphone preamps, the gain in the signal path (or open-loop gain) is fixed, equal to the maximum setting of the gain control(s) plus make-up gain for loop feedback, filters, etc (op amps typically have over 100dB of gain to allow for feedback). Because the gain is fixed, gain control is actually performed by variable attenuators or by variable loop feedback. As a result, the audio input signal is amplified by large amounts of fixed gain only to be cut back down to the level desired at the output.

     In the Gordon mic preamplifier, the gain in the signal path is variable, equal to the actual setting of the gain control, with no loop feedback, no attenuators, nor the associated redundant gain. In addition to gain, dynamic range and distortion are also optimized for each control setting. The audio signal at the input is amplified only by gain equal to and optimized for the gain control setting, significantly improving every aspect of sonic and measured performance.


OUTPUT LOAD COMPENSATION

     Outboard microphone preamp outputs see a wide range of loads due to signal frequency, cables, transformer inputs, and electronic inputs, varying from less than a hundred to over a million ohms. Distortion varies with load and can be minimized for a particular load by setting the operating parameters of the typical output stage. Change the load, however, and distortion increases.

     Automated output load compensation in the Gordon mic preamp couples an output load sensing circuit to a variable-parameter output stage.  The output signal is monitored to determine the load while the output stage parameters are adjusted accordingly to minimize distortion.


Mod5 int2.jpg (2475210 bytes)

Extensive support circuitry optimizes a minimalist signal path.  Symmetrical layout helps ensure matching channel characteristics and extremely low noise and crosstalk.


 
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