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John Hardy Jensen Twin Servo 990 Mic Preamp, 1 Channel  From John Hardy

1 Channel Mic-Pre

John Hardy Company


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Manufacturer's Description from John Hardy

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.

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 can be ordered with 1 to 4 channels. Additional channels can be easily added later up to the total capacity of the mainframe.


* 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:

* Fully Sealed Conductive Plastic Gain Control. Provides smooth continuous gain adjustments from 16dB to 60dB.

* 20 OHM MIC switch or 20dB PAD 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.

John Hardy Company

About Manufacturer

The John Hardy Company manufactures and distributes world class microphone preamplifiers and other signal processing products for recording professionals and project studio engineers. The audio circuitry, components and construction used on all John Hardy products are simple, elegant and superior. The most popular product, the M-1 mic preamp, has been impressing artists, engineers and listeners around the world since 1987. Typical comments include "Whoa!", "Even the producer could tell the difference!" and "I won't record without them!"


Voltage Gain Range +1dB 16 to 60 dBu
E.I.N., 20kHz bandwidth, unweighted RMS, 600 ohm load 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 ms
     Squarewave Risetime   2.2 µs
     Squarewave Tilt 20kHz 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.
     "Twin Servo" and "Comtran" are registered trademarks of Jensen Transformers, Inc.