Radial Engineering Jensen Twin-Servo 500 Series Mic Preamp

BH #RAMPA990 • MFR #R700 0111
Radial Engineering
Radial Engineering Jensen Twin-Servo 500 Series Mic Preamp
Key Features
  • 2 x Oversized Jensen Transformers
  • 2 x Jensen Dual 990 Op-Amps
  • Wide Frequency Response
  • Servos Eliminate Coupling Capacitors
The Radial Engineering Jensen Twin-Servo 500 Series Mic Preamp is a faithful recreation of Deane Jensen's original Twin-Servo 990 mic pre, regarded by many audio professionals as one of the finest preamps ever made.
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  • This item is noncancelable and nonreturnable.
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Radial Engineering R700 0111 Overview

  • 1Description
  • 2Jensen Mic Input Transformer
  • 3Jensen Dual Op-Amps
  • 4Jensen Output Transformer
  • 5180° Polarity-Reverse Switch
  • 610-Segment Meter
  • 7Dual-Gang Pot
  • 8High-Pass Filter
  • 9Pad
  • 1048V
  • 11Combo Input
  • 12Ground Lift Switch
  • 13Omniport
  • 14Full Enclosure

The Radial Engineering Jensen Twin-Servo 500 Series Mic Preamp is a faithful recreation of Deane Jensen's original Twin-Servo 990 mic pre, regarded by many audio professionals as one of the finest preamps ever made.

This mic preamp has pedigree. The circuit designed by the Jensen engineering team includes two cascaded 990 op-amps to share the load and provide 60 dB of clean gain. The two servos eliminate the need for signal-degrading capacitors in the audio path and allow for less than -120 dBu of noise.

Engineered for superior sound quality, the two oversized input and output Jensen transformers are a crucial part of the design. They contribute to lowering the noise floor and freeing the signal from hum and RF interference, while producing an extended frequency response and plenty of headroom.

Augmented by a 180º polarity-reverse switch, a -15 dB pad, and a high-pass filter that eliminates excessive low-end, the Twin-Servo opens musical tone-shaping possibilities. Other features include a dual-gang potentiometer for optimal gain, a 10-segment LED meter that gives instant visual feedback for the input signal and a 48V phantom power-activation switch to power condenser microphones. The front-panel Neutrik combo connector offers the choice of XLR microphone input and standard hi-Z 1/4" instrument input.

Re-imagined for today, this adaptation of the Jensen Twin-Servo fits the popular 500 series format.

Jensen Mic Input Transformer

The JT-16-PCJR is exceptionally quiet and linear from 5 Hz to 50 kHz with less than 0.06% distortion at 20 Hz

Jensen Dual Op-Amps

100% discrete audio signal path without any tone-shifting capacitors

Jensen Output Transformer

The JT-11-EM is linear from 2 Hz to 200 kHz with less than 0.001% distortion at 20 Hz

180° Polarity-Reverse Switch

Reverses pins 2 and 3 at the output to help phase-align microphones when two channels are in stereo use

10-Segment Meter

10-Segment Peak Indicator with Hold. Custom-designed circuit for greater VU accuracy

Dual-Gang Pot

Simultaneously controls the dual-990 op-amp topology for optimal gain at all levels

High-Pass Filter

Gentle high-pass filter may be inserted into the signal path to reduce excessive low-frequency content and control resonance


Reduces the input sensitivity by -15 dB when amplifying exceedingly high output sources


Activates the 48V phantom power supply for use with condenser microphones and active direct boxes

Combo Input

Combination balanced XLR mic input and 1/4" instrument input is mounted on front panel for ease of use

Ground Lift Switch

Set-and-forget rear-panel ground switch lifts the pin-1 ground at the XLR input


Available when used with the Radial Workhorse, the Omniport accesses a hi-Z instrument input

Full Enclosure

100% encased steel casing reduces magnetic interference from nearby modules that may cause noise pollution
UPC: 676101044238

Radial Engineering R700 0111 Specs

Circuit TypeTwo-stage variable gain, all discrete using original Deane Jensen circuit with IC DC servo
Jensen transformer-coupled input and output
Microphone InputTransformer-coupled, Jensen JT-15KE
Polarity Reverse180°
Frequency Response14 Hz to 85 kHz / 8 Hz to 100 kHz (±1 dB / ±3 dB)
Pad-15 dB
XLR ConfigurationAES spec: pin-1 ground, pin-2 (+), pin-3 (-)
Intermodulation Distortion0.004%
Dynamic Range91 dB
Input ImpedanceXLR Input: 1.3 kOhm
Instrument Input: 220 kOhms / unbalanced
Output Impedance75 Ohms
Maximum Output+22 dBu
Mic Pre Gain+60 dB
Common Mode Rejection-72 dB
Equivalent Input Noise-120 dBu @ maximum gain
Total Harmonic Distortion (THD) + N0.004%
Phantom Power48 VDC - 10 mA (as supplied by 500 frame)
High Pass Filter6 dB/octave, @ 150 Hz
Form Factor500 Series module
Power110 mA
Environmental ConditionsFor use in dry locations only between 5°C and 40°C (41°F and 104°F)
Dimensions5.25 x 1.5 x 7" (134 x 38 x 178 mm)
Weight1.75 lb (0.79 kg)
Packaging Info
Package Weight2.25 lb
Box Dimensions (LxWxH)8.976 x 6.614 x 1.89"
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