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John Hardy Company 990 2CH
2-Ch Jensen Twin Servo Microphone Preamp with 22-Position Switch


Transformer enhanced technology for superior sonic performance. Bringing science to sound.
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John Hardy Company 990 2CH
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Transformer enhanced technology for superior sonic performance. Bringing science to sound.

The Jensen Twin Servo 990 Mic Preamp is considered the world's finest mic preamp by audio experts. It's the ideal integration of advanced design software, hardware, engineering know-how, and carefully controlled 'golden ears' tests. It has earned high marks for sonic performance since its introduction in 1988.

The basic circuit was originally published as an application note by Jensen Transformers for their finest microphone input transformer, the JT-16-B. Each channel uses two precision 990C operational amplifier modules, developed and patented by Deane Jensen, to achieve one tenth the distortion and twice the bandwidth of a single stage design.

This special 2-channel version of the Jensen Twin Servo 990 Mic Preamp was originally developed for Sony Classical to provide high resolution switch-selectable gain control. It uses a 22 position rotary switch with gold plated contacts, providing a gain adjustment range of 18-60dB in steps of 2dB.

The Jensen Twin Servo 990 Mic Preamp has a 19" wide mainframe rack-mount chassis (1.75"H x 19"W x 8"D) and is only available as a fixed two channel version, unlike the standard version.

The John Hardy Company 2-Ch Jensen Twin Servo Microphone Preamp Features:

  • JT-16-B Input Transformer. Jensen's best mic input model.
  • Two 990 Discrete Op-Amps Per Channel. Faster, quieter, more powerful and better sounding than typical monolithic op-amps.
  • Elimination Of All Coupling Capacitors From The Signal Path. Results in less degradation of the audio signal.
  • JT-11-BMQ Output Transformer. Jensen's best line output transformer.
  • Input Bias Current Compensation Circuitry And DC Servo Circuitry. Eliminates signal degrading coupling capacitors.
  • Standard Features:
    • 22 Position Rotary Gain Switch. Provides accurate and repeatable gain settings from 18dB to 60dB in 2dB steps.
    • 20 OHM MIC switch or 20dB PAD switch.
    • POLARITY REVERSE switch.
    • PHANTOM POWER switch.
    • All Front Panel Switches Are LED Illuminated.
    • Gold Plated XLR Connectors for maximum reliability.
    • Ground Lift Switch On Each Channel. Helpful for eliminating ground loops.
    • VU-1 meter. Very accurate and informative 20 segment LED meter, with separate Peak LED, for monitoring preamp output.
    • Toroidal Power Transformer With Additional Shielding. Eliminates hum problems so no external power supply is needed.
    • Universal Power Supply. Internal switch provides six primary voltage choices to accommodate use anywhere in the world.
    • Chassis Ground Isolation Switch. Helpful for eliminating ground loops.
    • Pin 2 Or Pin 3 High. Internal jumpers make changes in the field easy.

The John Hardy Company 2-Ch Jensen Twin Servo Microphone Preamp Specifications:

  • Voltage Gain Range  +1dB  18 to 60  dB
  • E.I.N., 20-20kHz bandwidth, unweighted, 60dB gain, 0dBu = 0.775V  150 Ohm source  -128.7  dBu
  • Frequency Response, ref: 1kHz:
    • 20Hz  -0.05 typ, -0.1 max  dB:
    • 20kHz  -0.05 typ, -0.1 max  dB
    • 0.4Hz and 140kHz  -3  dB
  • Time Domain Response:
    • Deviation From Linear Phase (maximum)  20Hz to 20kHz  +2  deg
    • Group Delay  20Hz to 120kHz  2.16 +0.05  µs
    • Squarewave Risetime: 2.2  µs
    • Squarewave Tilt  20Hz  5.8  %
  • Total Harmonic Distortion (note 1)  
    • Output Level +4dBu, any gain setting:
      • 100Hz to 20kHz  0.001 typ, 0.003 max  %
      • 20Hz  0.036 typ, 0.100 max  %
    • Input Level +8dBu (note 2)
      • 100Hz to 20kHz  0.001 typ, 0.003 max  %
      • 20Hz  0.120 typ, 0.300 max  %
  • Common Mode Rejection Ratio:
    • 60Hz  125  dB
    • 1kHz  100  dB
    • 10kHz  80  dB
  • Common Mode Input Voltage: +300  V-pk
  • Optimum microphone Impedance (switch selectable): 150/20  Ohms
  • Input Impedance, +15% max  20Hz to 20kHz  1.27  k Ohms
  • Phantom Power:
    • Voltage:  +52  VDC
    • Current (maximum): 9.5  mA
  • Maximum Output Level:  75 Ohm load  +24  dBu
  • Output Load Impedance Range  minimum/nominal  150/600  Ohms
  • Output Source Impedance  20Hz to 20kHz  70 +5  Ohms
  • Power Requirements, 4 Channels:
    • +15%  100, 120, 140, 200, 220, 240  VAC
    • 48 to 66  Hz
    • 25  Watts
  • Dimensions (note 3): 1.75H x 19W x 8D  Inches
  • Notes:
    • Unless otherwise specified: 25° C ambient, 150 Ohm source, 600 Ohm load.
    • (1) Low frequency response distortion is almost entirely 3rd harmonic.
    • (2) Worst case of maximum possible input at minimum gain with unclipped output.
    • (3) Handles extend 1" beyond the front panel.

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