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Transformer enhanced technology for superior sonic performance. Bringing science to sound.

The JensenTwin 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.

The 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

The 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 for eliminating 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 Co. Jensen Twin Servo 990 Three Channel Mic Pre

  • John Hardy Jensen Twin Servo 990 Mic Preamp
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