Radial Engineering Twin-Servo User's Guide

®

True to the Music

Jensen Twin-Servo

500 Series Module

Made in Canada

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™

Radial Engineering Ltd.
1588 Kebet Way, Port Coquitlam, British Columbia, Canada, V3C 5M5

Tel: [phone] • Fax: [phone] • Email: [e-mail]

www.radialeng.com

Radial

990

opamp

JENSEN TWIN

User Guide

Radial® Jensen Twin-Servo 500™ User Guide

Table of Contents Page

Feature Set .................................................................... 1

Overview ........................................................................ 2

Making Connections ....................................................... 3

The Control Panel .......................................................... 4

Ground Lift and Omniport ............................................... 5

Applications .................................................................... 6

Block Diagram ................................................................ 7

Specications ................................................................. 8

Warranty ............................................................Back cover

Thank you for purchasing the Jensen Twin-Servo 500™

series mic preamp. We are condent that as you become

familiar with and gain experience using this device, you will

quickly nd that it is an exceptional sounding preamp for

any application.

Although the Twin-Servo has been designed to be super

easy to use, we urge you to take a few minutes to read
the manual to ensure you gain familiarity with all of the
features and functions that make it unique. If after you

have done so, you nd yourself looking for extra details,
please visit the Twin-Servo FAQ page on the Radial web

site. This is where we post updates and answer questions

from other users that can shed light on various subjects. If
afterwards you still do not nd the appropriate answer, feel
free to send us an email and we will do our very best to

answer in short order.

Now get ready to plug into what may well be the most
transparent and detailed sounding mic preamplier you

have ever heard.

®

FEATURE SET

1. 10 SEGMENT METER: Custom designed cir-

cuit for greater VU meter accuracy.

2. GAIN CONTROL: Dual gang pot simultane­ously controls the dual 990 op-amp topology
for optimal gain at all settings. Stepped attenu­ation allows for easy recall of settings.

3. 180°: Reverses pins-2 and 3 at the output to
help phase align microphones when two chan­nels are in stereo use.

4. HIGH PASS FILTER (HPF): Gentle high-pass

 lter may be inserted into the signal path to

reduce excessive low frequency content and
control resonance.

5. PAD: Reduces the input sensitivity by -15dB
when amplifying exceedingly high output
sources.

6. 48V: Activates the 48V phantom power supply
for use with condenser microphones and ac-

tive direct boxes.

7. COMBO INPUT: Combination balanced XLR

mic input and 1/4” instrument input is mounted
on front panel for ease of use.

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

9. JENSEN DUAL 990 OPAMPS: 100% discrete

audio signal path without any tone shifting ca­pacitors.

10. JENSEN OUTPUT TRANSFORMER: The JT-

11-EM is linear from 2Hz~200kHz with less
than 0.001% distortion at 20Hz.

11. GROUND LIFT: Set and forget rear panel

ground switch lifts the pin-1 ground at the XLR

input.

12. JENSEN MIC INPUT TRANSFORMER: The

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

True to the Music

Made in Canada

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JENSEN TWIN

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OMNIPORT: INSTRUMENT INPUT

10 11

1

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Radial Engineering Ltd.

1

Jensen Twin-Servo 500™ Module

True to the Music

®

OVERVIEW

The Radial Jensen® Twin-Servo™ is a high-performance microphone preamp designed for

exceptional frequency response, detail, and transparency. It’s also remarkably easy to use;
simply plug in your mic, adjust the gain, and you’re ready to record. The Twin-Servo has
features common to many mic preamps, such as a 180º polarity reverse, high-pass  lter,

input pad, and 48V phantom power. However, it’s what‘s under the hood that really sets the

Twin-Servo apart: two of Deane Jensen’s famous JE-990 discrete operational ampli ers, two

servos that eliminate all coupling capacitors, and two industry-leading Jensen transformers.

The Twin-Servo 500 has been meticulously designed to reproduce Deane Jensen’s original
Twin-Servo 990 mic pre, regarded by many audio professionals as the  nest preamp ever
made. The dual JE-990 op-amps allow for maximum ef ciency and lowest noise at all signal

levels, while the servos eliminate the need for signal degrading capacitors in the audio

path. Jensen transformers at the input and output deliver an amazing amount of bandwidth,

extending the natural low end and providing for huge amounts of headroom. The Twin-Servo
can provide up to 60dB of gain, perfect for source material with a high dynamic range. We

encourage you to try the Twin-Servo on a variety of sources as we are con dent you will be

impressed with the results.

TYPICAL SETUP

Radial Engineering Ltd.

Made in Canada

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OMNIPORT: INSTRUMENT INPUT

Radial

990

opamp

JENSEN TWIN

TWIN-SERVO Q4 EQ

2

KOMIT

COMPRESSOR

Jensen Twin-Servo 500™ Module

®

INPUT

OMNIPORT

FEED

LINK

123456

OFF

OFF

CARD SLOT 1CARD SLOT 3CARD SLOT 5CARD SLOT 7 CARD SLOT 2CARD SLOT 4CARD SLOT 6CARD SLOT 8

OUTPUT

INPUT

ON

ON

MONO

Made in Canada

MAIN

MON

48V PHANTOM

+16V / -16V

True to the Music

MAKING CONNECTIONS

Before making connections, ensure your audio
system is turned off and volume levels turned
down. Hot swapping or inserting the module into
a 500 series power rack when power is on is not
recommended as it can harm some equipment and
shorten the lifespan of the card edge connectors.
Gently slide the Twin-Servo module into place
ensuring you align the card edge with the 15-pin
receptacle. If you have a newer Radial Workhorse,
the nylon guides make this easy. The Twin-Servo

comes with a pair of handy ThumbSet™ thumb
screws. These should be hand-tightened to secure

Radial ThumbSet™

knurled screws are
included for easy
installation.

the module in place before use.

Your power rack will likely be equipped with XLR inputs and outputs for each strip. Connect
your microphone to either the female XLR input on the rear panel or the handy front panel
Combo connector. These are wired in parallel and only one should be used at any one time.
Connect the output using the male XLR on the power rack to your recording system. Ensure

the volume levels on your recording system are turned off and set the volume control on the
Twin-Servo fully counter-clockwise to 7 o’clock. You are now ready to turn on your power rack
and recording system. Note that there is no power switch on the Twin-Servo. As soon as your
power rack is turned on, the Twin-Servo will spring to life.

Made in Canada

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OMNIPORT: INSTRUMENT INPUT

Output

If you are using a condenser microphone, activate the phantom power by depressing the
front panel 48V switch. All other switches should be in the out position. Slowly increase the

Radial

990

JENSEN TWIN

opamp

REAR PANEL

INPUT

(WORKHORSE)

volume on your recording system and then turn up the volume on the Twin-Servo. It is always

best to test at low volumes as this will reduce the opportunity of damaging more sensitive
components such as tweeters should a connection be improperly seated. You should now
hear the audio and see activity on the 10 bar LED meter.

Radial Engineering Ltd.

3

Jensen Twin-Servo 500™ Module

True to the Music

®

THE CONTROL PANEL

The 10 Segment LED

The Twin-Servo is equipped with a 10 segment LED meter that gives you instant visual

feedback of the incoming input signal. Although the Twin-Servo is unlikely to ever distort,

keeping the signal within normal working range will ensure optimal signal-to-noise. Turn up

the level control by testing for maximum volume. When in the red, turn down for headroom

and you are set to go.

180º Polarity Reverse

Another handy feature on the Twin-Servo is the polarity reverse switch. This can be used to
better phase-align two sources such as two microphones that may be spaced differently in
a room or when combining a microphone with a direct box. You can also increase the width
of the stereo eld when the two mics are out of phase. It is also great for matching up older

audio gear that may not follow the AES standard with pin-2 hot.

High Pass Filter (HPF)

One of the truly unique advantages with the Twin-Servo is that amazing frequency response.

Most preamps are unable to effectively reproduce frequencies below 20Hz. The Twin Servo
actually measures down to 5Hz! With so much bass, you will hear low end like never before.
The downside is that with so much bass to work with, it may be excessive, particularly when

recording several acoustic instruments together. The solution: reduce the resonance and

excessive bass by engaging the high-pass lter. This is one of the most practical features
on the Twin-Servo. When engaged, it gently rolls off bottom end below 80Hz and can help

clean up the mix.

High-Pass Filter Response

+10

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20 20k50 100 200 500 1k 2k 5k 10k

Hz

-15dB Pad

A pad is primarily used to reduce the preamp’s input sensitivity so that when confronted with
an extra high level output signal, it will not overload the input stage of the mic preamp and

cause distortion. As the Twin-Servo has so much headroom, it will be unlikely that you will
ever need to use this feature. But it’s there just in case.

48V Phantom

This switch activates standard 48V phantom power to remotely feed your condenser mic,

active direct box or McBoost mic booster. When on, 48 volts DC is sent from the Twin-Servo

using the pin-1 (ground) and pin-2 (hot) wires to power the connected device. Simply engage

if needed. Always make sure to turn down the levels before engaging phantom power.

Ground Lift

Radial Engineering Ltd.

4

Jensen Twin-Servo 500™ Module

®

INPUT

OMNIPORT

FEED

LINK

123456

OFF

OFF

CARD SLOT 1CARD SLOT 3CARD SLOT 5CARD SLOT 7 CARD SLOT 2CARD SLOT 4CARD SLOT 6CARD SLOT 8

OUTPUT

INPUT

ON

ON

MONO

Made in Canada

MAIN

MON

48V PHANTOM

+16V / -16V

There is a hidden ground lift switch (mini slider) that lets

you lift the ground on the front and rear XLR inputs. As the

Twin-Servo is equipped with an input transformer, you will

likely never need to lift the ground. This should be set in

the upward position. However, a unique situation could arise
where you may incur noise. To lift the ground, you have to
pull the module from your power rack and then move the
slider downwards towards the 15-pin card edge connector.
The ground lift switch does not affect the ¼” guitar input

portion of the Combo jack or the output side of the Twin-

Servo. Note that when the ground is lifted, the Twin-Servo
will no longer pass 48V phantom power to your microphone.

HI-Z Input and Omniport™

The Twin-Servo has two instrument input options. The

immediately obvious one is on the front panel - as part of the
Neutrik Combo connector. Note that this is a standard hi-Z

¼” instrument input and using a 1/4” TRS connector is not
recommended. The second is via the Omniport™ for those
that are equipped with a Radial 500 series power rack. Both

are connected in parallel but as soon as you engage the
front panel jack, it will automatically switch the rear panel

¼” input off.

True to the Music

Switch Located Here

Radial Engineering Ltd.

REAR PANEL INPUT

(WORKHORSE)

WARNING NOTICE TO USER!

Although preventative safety measures have been designed into Radial 500 series

products we strictly advise against hot-swapping modules or plugging and
unplugging them when the Workhorse or other 500 series rack are powered on. Hot
swapping can cause connection sparks at the card-edge connector that could send
damaging transients to other equipment. This also greatly reduces the life span of the
contacts. Damage due to hot swapping is not covered under warranty. There are no

user serviceable parts inside.

5

Jensen Twin-Servo 500™ Module

True to the Music

APPLICATIONS

Using the Twin-Servo with an active DI

When recording live, capturing the direct feed from an instrument can provide much more

consistent results as bleed from other instruments can be eliminated. Connect a piezo
transducer to the Radial PZ-DI and send this to the Twin-Servo for amazing bottom end!

Made in Canada

OUTPUT LEVEL-VU

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OMNIPORT: INSTRUMENT INPUT

Radial

990

opamp

JENSEN TWIN

®

Using the Twin-Servo with a ribbon mic

Most modern ribbon microphones have plenty of output and can connect directly to the Twin-

Servo’s low noise circuitry. When using old vintage mics, add the Radial McBoost to increase

the output by up to 25dB for a total of about 85dB of gain!

Made in Canada

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OMNIPORT: INSTRUMENT INPUT

Radial

990

opamp

JENSEN TWIN

Radial Engineering Ltd.

6

Jensen Twin-Servo 500™ Module

®

BLOCK DIAGRAM*

True to the Music

* Subject to change without notice.

Radial Engineering Ltd.

7

Jensen Twin-Servo 500™ Module

True to the Music

SPECIFICATIONS*

Circuit Type: .................................... 100% discrete using original Deane Jensen circuit with IC DC servo

Microphone Input: ..........................................................................Transformer coupled, Jensen JT-15KE

Power: ............................................................................................................................................. 110mA

Frequency Response: ...................................................... 14Hz to 85kHz / 8Hz to 100KHz (±1dB / ±3dB)

Input Impedance - XLR:.....................................................................................................................1.3kΩ

Mic Preamp Gain: .............................................................................................................................+60dB

Maximum Output: ...........................................................................................................................+22dBu

Output Impedance: .............................................................................................................................. 75Ω

Common Mode Rejection (CMRR): .................................................................................................. -72dB

Equivalent Input Noise (EIN): ...........................................................................-120dbu @ maximum gain

Dynamic Range: .................................................................................................................................91dB

Total Harmonic Distortion (THD+N): ...............................................................................0.004% @ +4dBu

Intermodulation Distortion:..............................................................................................0.004% @ +4dBu

Instrument Input

Input Impedance - Instrument:.....................................................................................220kΩ, unbalanced

Instrument Preamp Gain: ............................................................................................+60dB, unbalanced

Control Panel

Meter: ...............................................................................................10 segment peak indicator with hold

Polarity Reverse: .................................................................................................................................180º

Pad: .................................................................................................................................................. -15dB

High-Pass Filter: ............................................................................................. 6dB/octave, -3dB @ 150Hz

Phantom Power: ..................................................................... 48VDC - 10mA (as supplied by 500 frame)

XLR Conguration: ................................................................. AES spec: pin-1 ground, pin-2 (+), pin-3 (-)

Ground Lift (rear panel): ...................................................................................Lifts ground on XLR inputs

Mechanical

Weight: ............................................................................................................................... 1.75lbs (0.8kg)

Size:...........................................................................................................................7 x 5.5 x 1.5 (inches)

Warranty: ................................................................................................................... 3 years, transferable

®

* Subject to change without notice.

Radial Engineering Ltd.

8

Jensen Twin-Servo 500™ Module

THREE YEAR TRANSFERABLE LIMITED WARRANTY

RADIAL ENGINEERING LTD. (“Radial”) warrants this product to be free from defects in material and
workmanship and will remedy any such defects free of charge according to the terms of this warranty.
Radial will repair or replace (at its option) any defective component(s) of this product (excluding fi nish
and wear and tear on components under normal use) for a period of three (3) years from the original
date of purchase. In the event that a particular product is no longer available, Radial reserves the
right to replace the product with a similar product of equal or greater value. In the unlikely event that
a defect is uncovered, please call 604-942-1001 or email [e-mail] to obtain a RA
number (Return Authorization number) before the 3 year warranty period expires. The product must be
returned prepaid in the original shipping container (or equivalent) to Radial or to an authorized Radial
repair centre and you must assume the risk of loss or damage. A copy of the original invoice showing
date of purchase and the dealer name must accompany any request for work to be performed under
this limited and transferable warranty. This warranty shall not apply if the product has been damaged
due to abuse, misuse, misapplication, accident or as a result of service or modifi cation by any other
than an authorized Radial repair centre.

THERE ARE NO EXPRESSED WARRANTIES OTHER THAN THOSE ON THE FACE HEREOF

AND DESCRIBED ABOVE. NO WARRANTIES WHETHER EXPRESSED OR IMPLIED, INCLUDING

BUT NOT LIMITED TO, ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR

A PARTICULAR PURPOSE SHALL EXTEND BEYOND THE RESPECTIVE WARRANTY PERIOD

DESCRIBED ABOVE OF THREE YEARS. RADIAL SHALL NOT BE RESPONSIBLE OR LIABLE
FOR ANY SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES OR LOSS ARISING FROM
THE USE OF THIS PRODUCT. THIS WARRANTY GIVES YOU SPECIFIC LEGAL RIGHTS, AND

YOU MAY ALSO HAVE OTHER RIGHTS, WHICH MAY VARY DEPENDING ON WHERE YOU LIVE
AND WHERE THE PRODUCT WAS PURCHASED.

To meet the requirements of California Proposition 65, it is our responsibility to inform you of the following:

WARNING: This product contains chemicals known to the State of California to cause

cancer, birth defects or other reproductive harm.

Please take proper care when handling and consult local government regulations before discarding.

This product is intended for professional use only.

The user should be familiar and experienced with

!

the 500 series rack and module format.

®

Radial Engineering Ltd.

1588 Kebet Way, Port Coquitlam BC V3C 5M5
tel: [phone] • fax: [phone]
[e-mail] • www.radialeng.com

Radial® Twin-Servo 500™ Module User Guide - Part #: R870 1257 10 / 11-2017

Copyright 2017 Radial Engineering Ltd. All rights reserved.
Specifi cations and appearances subject to change without notice.

www.radialeng.com