Radial Engineering


Radial Jensen Twin Servo Mic Pre 500-series module

The Radial Jensen® Twin-Servo & 500 series preamplifier is an updated version of what may well be the most spectacular preamp ever made. Originally developed by industry icon Deane Jensen in 1988, the Twin-Servo 500 is an adaptation that fits the popular 500 series format.

    • Features:

      Exceptionally wide frequency response from 0.5Hz to 150kHz

      Twin-servo topology eliminates capacitors in the signal path

      Virtually zero phase shift or bandwidth limitation

      Oversized Jensen® transformers for maximum headroom

      Originally developed by industry icon Deane Jensen in 1988, the Twin-Servo 500 is an adaptation that fits the popular 500 series format. The design begins with the legendary performance of two 100% discrete 990 op-amps cascaded in tandem to deliver 60dB of gain with less than 1/10th the distortion and twice the bandwidth of a single stage design. This maximizes the gain-margin so that no matter what the input, the lowest possible distortion will be realized. This also reduces noise at mid and low levels, a critical advantage for those that record with a wide dynamic range. In order to minimize phase distortion and retain the delicate balance of fundamentals with harmonics, all capacitors have been removed from the audio signal path and replaced by two DC servo feedback circuits. This not only reduces low-frequency noise, but also eliminates the ugly distortions associated with electrolytic capacitors that are especially degrading to low-level microphone signals when used to block phantom power in transformerless designs. To deliver the widest possible bandwidth, Jensen transformers are placed at both the input and output producing a frequency response that extends from 0.2Hz to 150kHz. The transformers further benefit with unmatched common-mode noise rejection from offending devices such as power supplies, light dimmers and motors that may be connected to the same power service.

    • Specifications:

      Circuit type:

      Two stage variable gain all discrete using original Deane Jensen circuit with IC DC servo. Jensen transformer coupled input and output.

      Frequency response:

      14Hz to 85kHz / 8Hz to 100kHz (±1dB / ±3dB)

      Total harmonic distortion:


      Dynamic range:


      Input impedance - XLR:  


      Input impedance - instrument:  

      220kΩ, unbalanced

      Output impedance:  


      Maximum output:


      Mic preamp gain:


      Common mode rejection (CMRR):


      Equivalent input noise (EIN):

      -120dBu @ maximum gain

      Total Harmonic Distortion (THD+N):


      Intermodulation distortion:




      Microphone input:

      Transformer coupled, Jensen JT-15KE


      10 segment peak indicator with hold

      Polarity reverse:




      Ground lift (rear panel):

      Lifts ground on XLR inputs

      XLR configuration:

      AES spec: pin-1 ground, pin-2 (+), pin-3 (-)





      Phantom power:

      48VDC - 10mA (as supplied by 500 frame)

      High pass filter:

      6dB/octave @ 150Hz


      500 Series module


      5.25" x 1.5" x 7" (134mm x 38mm x 178mm)


      1.75lb (0.79 kg)

      Shipping size:

      6.75" x 1.875" x 9" ( 171mm x 48mm x 229mm)

      Shipping weight:

      2.20lb (0.997 kg)


      For use in dry locations only between 5°C and 40°C


      Radial 3-year, transferable

      Specifications are subject to change without notice.