John Hardy Jensen Twin Servo 990 2-Channel Microphone Preamp (Stepped Switch)

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Product Code: 2403
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John Hardy Jensen Twin Servo 990 2-Channel Mic Preamp (Stepped Switch)

The John Hardy Jensen Twin Servo 990 2-Channel Microphone Preamp with stepped switch features a 22 Position Rotary Gain Adjustment. It's the ideal integration of advanced design software, hardware, engineering know-how, and carefully controlled 'golden ears' tests.

The Jensen Twin Servo 990 Mic Preamp is considered the world's finest mic preamp by audio experts. It is perhaps the epitome of transformer enhanced technology used to achieve superior sonic performance. Bringing science to sound. 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.

John Hardy Jensen Twin Servo 990 2-Channel Microphone Preamp (Stepped Switch version) Features


Design Highlights:


  • 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.
  • 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.

Special Note

John Hardy pre-amps are built-to-order boutique devices and in most cases there is usually a short wait. Waiting for your Hardy preamp is akin to waiting for a custom-built instrument - only the wait-time is much shorter for the Hardy. As a rule of thumb we typically give an estimated delivery time of 2-Weeks, but we've sometimes seen them ship in a day or two. Regardless, if you must meet a deadline, please email us and we'll work to find out where your order would be in the production line. Please also note that the 20 Ohm option can result in slightly longer ETAs - do to the addition hand wiring needed.

What We Think - John Hardy Jensen Twin Servo 990 Review

"John Hardy's passion for quality has put his name at the top of the list of boutique designers of microphone preamplifiers, and has his creations at the top the lists for most coveted gear by professionals who are in-the-know and who desire the very best examples of design philosophy and implementation. John's friendship with the late Deane Jensen over the years (and Deane having been impressed with John's work with the M-1) resulted in John being contracted by Jensen to build the Twin Servo 990 preamp based on the packaging of the M-1. However, this particular special 2-channel version with 22-position switches was originally contracted by Sony Classical who desired the extra purity of this particular gain control design. The gain switches are so large that they take up what would be preamp slots 2 and 4 in the normal 4-channel chassis version of the Twin Servo 990. As a result, this 2-Channel Stepped Switch version of the John Hardy Jensen Twin Servo 990 could be considered to be the ultimate implementation of Deane Jensen's op-amp and transformer designs and John Hardy's commitment and passion for quality."

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