Symetrix 306 User manual

306 Preamp/Ducker
User s Guide
306

i
Table of Contents
Chapter 1 Introduction 1
Chapter 2 Operator Safety Summary 2
Chapter 3 Fast Setup 3
Chapter 4 Front Panel Overview 4
Chapter 5 Rear Panel Overview
Chapter 6 Applications 7
Chapter 7 Troubleshooting 9
Chapter 8 Specifications 11
Chapter 9 Block Diagram 12
Chapter 10 Warranty and Service 13
Chapter 11 Declaration of Conformity 15
Rev A, 30 April, 1999
Symetrix part number 5330 -0A00
Subject to change without notice.
'1999, Symetrix, Inc. All right reserved.
Symetrix is a registered trademark of Symetrix, Inc.
Mention of third-party products is for informational
purposes only and constitutes neither an endorsement nor
a recommendation. Symetrix assumes no responsibility
with regard to the performance or use of these products.
Under copyright laws, no part of this manual may be
reproduced or transmitted in any form or by any means,
electronic or mechanical, including photocopying,
scanning, recording or by any information storage and
retrieval system, without permission, in writing, from
Symetrix, Inc.
6408 216th St. SW
Mountlake Terrace, WA 98043 USA
Tel [phone]
Fax [phone]
Email: [email protected]
306

306
1
IntroductionChapter 1
Front panel
Rear panel
OUTPUT
PWR
0
GAIN (dB)
-20
CLIP
PROGRAM
PAGE
RELEASE
2 Sec
.5 Sec 4 Sec
MIX
+20
DUCKER
HOLD
2 Sec
4 Sec
BYPASS .25 Sec-600
-20
-40
THRESHOLD (dBv) DEPTH (dB)
-30
PREAMP/
DUCKER
306
DUCK
OFF
LINE
ON
MIC
MIC/LINE
306
PREAMP/DUCKER
PHANTOM
PROGRAM INPUTS
RIGHT
LEFTRIGHT
PAGE INPUTPAGE MIX OUTPUTS
LEFT
RIGHT
RIGHT
DIRECT OUT
INPUT
POWER
SERVICABLE PARTS.
POWER SUPPLY ONLY.
SYMETRIX PS-3
CONNECT TO
SUPPLY ONLY.
OR PS-3E POWER
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC.,
WA, USA. THIS PRODUCT CONTAINS NO USER
MANUFACTURED BY SYMETRIX INC., LYNNWOOD
LYNNWOOD, WA, USA. RÉFÉREZ TOUTE
RÉPARATION À UN TECHNICIEN QUALIFIÉ.
Congratulations on your purchase of the Symetrix 306 Preamp/Ducker. Like the other units in the
Symetrix 300 series the 306 is designed to provide extremely versatile controls within a streamlined
half-rack sized housing. Once installed in a paging/foreground music system the 306 offers precise
adjustments to automatically reduce the gain of a program signal when paging occurs. This allows
the page to be heard clearly without having to compete with program material such as audio from a
CD radio TV or other sources.
The Symetrix 306 has a selectable mic/line page input with phantom power available for condenser
microphones. When the mic switch position is selected preamplification is applied to the page
microphone signal to bring it up to line level. A line-level direct page output is also provided by
the 306 for added flexibility. The left and right program inputs and mix outputs of the 306 allow for
mono or stereo operation.
Front panel controls tailor the amount and duration of ducking balance the mix between page and
program signals and provide overall volume control.
We recommend that you read this guide cover-to cover. You will find the answer to most of your
questions inside. If you have technical questions beyond the scope of this manual please contact
our Customer Service Department at:
Phone:[phone]
Fax:[phone]
Email: [email protected]
Website: www.symetrixaudio.com

306
2
Operator Safety Summary Chapter 2
Terms
Several notational conventions are used in this
manual. Some paragraphs may use Note Caution
or Warning as a heading. Certain typefaces and
capitalization are used to identify certain words.
These are:
Note Identifies information that needs
extra emphasis. A Note generally
supplies extra information to help
you to better use the 306.
Caution Identifies information that, if not
heeded, may cause damage to the
306 or other equipment in your
system.
Warning Identifies information that, if
ignored, may be hazardous to your
health or that of others.
CAPITALS Controls switches or other markings
on the 306 s chassis.
Boldface Strong emphasis.
Equipment Markings
AVIS:
NE PAS OUVRIR
Il ne se trouve a l’interieur aucune piece pourvant entre reparée l’usager.
SEE OWNERS MANUAL. VOIR CAHIER D’INSTRUCTIONS.
S’adresser a un reparateur compétent.
RISQUE DE CHOC ELECTRIQUE
No user serviceable parts inside. Refer servicing to qualified service personnel
.
CAUTION
WARNING:
TO REDUCE THE RISK OF FIRE OR
ELECTRIC SHOCK DO NOT EXPOSE
THIS EQUIPMENT TO RAIN OR MOISTURE
DO NOT OPEN
RISK OF ELECTRIC SHOCK
The lightning flash with arrowhead symbol within an
equilateral triangle is intended to alert the user of the
presence of uninsulated dangerous voltage within
the product s enclosure that may be of sufficient
magnitude to constitute a risk of electric shock to
persons. The exclamation point within an equilateral
triangle is intended to alert the user of the presence of
important operating and maintenance (servicing)
instructions in the literature accompanying the product
(i.e. this manual).
Caution To prevent electric shock, do not use the
polarized plug supplied with the unit with
any e tension cord, receptacle, or other
outlet unless the blades can be fully
inserted.
ImportantSafetyInstructions
Please read and keep these instructions. Heed
and follow all warnings and instructions.
Install in accordance with the manufacturer s
instructions.
Power Source This product is intended to
operate from a Symetrix PS-3 or PS-3E power
supply.
Grounding The chassis of this product is
grounded through the grounding conductor of
the PS-3 or PS-3E power cord. To avoid electric
shock plug the power cord into a properly wired
receptacle before making any connections to the
product. A protective ground connection by
way of the grounding conductor in the power
cord is essential for safe operation. Do not defeat
the safety purpose of the grounding plug. The
grounding plug has two blades and a third
grounding prong. The third prong is provided for
your safety. When the provided plug does not fit
your outlet consult an electrician for replacement
of the obsolete outlet.
Danger from oss of Ground If the protective
ground connection is lost all accessible conduc-
tive parts including knobs and controls that may
appear to be insulated can render an electric
shock.
Proper Power Cord Use only the power cord
and connector specified for the product and your
operating locale. Use only a cord that is in good
condition. Protect the power cord from being
walked on or pinched particularly at the plug
convenience receptacle and the point where the
cord exits from the apparatus.
Operating ocatio. Do not operate this equip-
ment under any of the following conditions:
explosive atmospheres in wet locations in
inclement weather improper or unknown AC
mains voltage or if improperly fused. Do not
install near any heat source such as radiators
heat registers stoves or other apparatus
(including amplifiers) that produce heat. Unplug
this apparatus during lightning storms or when
unused for long periods of time.
Stay Out of the Box To avoid personal injury (or
worse) do not remove the product covers or
panels. Do not operate the product without the
covers and panels properly installed. Only use
accessories specified by the manufacturer. Clean
only with a damp cloth.
User-serviceable parts There are no user
serviceable parts inside the 306. In case of
failure refer all servicing to the factory. Servic-
ing is required when the 306 has been damaged
in any way such as when a power supply cord or
plug is damaged liquid has been spilled or
objects have fallen into the apparatus the
apparatus has been exposed to rain or moisture
does not operate normally or has been dropped.

306
3
Fast First-Time Setup
This section provides simple instructions to begin using the 306. Please refer to later chapters for
detailed descriptions of product features and applications.
¥ Set the THRESHOLD control to the 9:00 position.
¥ Set the DEPTH control to the 12:00 position.
¥ Set the HOLD and RELEASE controls to the 9:00 position.
¥ Set the MIX control to the 12:00 position.
¥ Set the GAIN control completely counterclockwise.
¥ Connect the 306 to an appropriate source of AC power using the Symetrix PS-3 or PS-3E
power supply provided with your 306.
¥ Set the PHANTOM POWER and MIC/LINE switches (located on the back panel) to the correct
positions.
¥ Connect your audio inputs and outputs.
¥ Turn up the GAIN control until the desired volume level is reached.
¥ Now read the rest of this manual
Fast Setup
Chapter 3

306
4
Front Panel Overview Chapter 4
OUTPUT
PWR
0
GAIN (dB)
-20
CLIP
PROGRAM
PAGE
RELEASE
2 Sec
.5 Sec 4 Sec
MIX
+20
DUCKER
HOLD
2 Sec
4 Sec
BYPASS .25 Sec-600
-20
-40
THRESHOLD (dBv) DEPTH (dB)
-30
PREAMP/
DUCKER
306
DUCK
DuckerControls
DUCK LED — This LED lights to indicate that the page signal has exceeded the ducker threshold
(see THRESHOLD below) and ducking of the program material is occurring.
THRESHOLD — This control adjusts the sensitivity of the ducker circuitry to signals at the page
input. Turning this control counterclockwise causes the ducker to be very responsive to a wide
dynamic range of page signals. This can be desirable if you want the ducker to react to page
signals that range from very quiet to very loud. Turning the THRESHOLD control clockwise causes
the ducker to only react to higher-level page signals. This can be useful in preventing unwanted
lower-level signals from triggering the ducker.
DEPTH — The DEPTH control governs the amount by which the program material will be decreased
(ducked) when the ducker s threshold has been exceeded. Maximum ducking occurs when this
control is set counterclockwise. The program material will then be ducked by 60dB (virtually
muted) whenever the signal at the page input exceeds the ducker s threshold. As the DEPTH
control is turned clockwise the amount of ducking that occurs when the ducker has been triggered
decreases. When the DEPTH control is completely clockwise (bypass) no ducking will occur even
when the ducker s threshold has been exceeded.
HOLD — This control determines the amount of time that ducking will continue at the level deter-
mined by the DEPTH control once the page signal has dropped back below the ducking threshold.
As this control is turned clockwise the hold time is increased. This causes the program material to
be ducked for a longer amount of time before the ducker releases and allows the program signal to
return to normal. Turning the control counterclockwise creates a shorter hold time which causes
the ducker to release more quickly. Longer hold times contribute to overall smoothness whereas
shorter hold times allow the program level to return to normal more quickly.
RELEASE — The RELEASE control determines the amount of time that it will take for the program
material to be restored to its original ( unducked ) level once the hold time has passed. Setting
this control clockwise
causes a longer smoother
return to normal program
level. Setting this control
counterclockwise allows
the program level to
recover more swiftly after a
page. Long release times
also contribute to an
overall smooth sound and
shorter release times allow
for a swifter return to
normal program levels.
Page
Input
Level
Program
Output
Level
Duck Level
(Depth Control)
Threshold Level
Hold Time
Release Time

306
5
OutputControls
MIX — This control sets the relative volume levels of the page signal and the program material. If
the page signal is coming through too softly relative to the program material turn this control
counterclockwise until the desired balance is achieved. If the page signal is too loud compared to
the program material turn this control clockwise until the desired balance is achieved.
CLIP LED — This LED is a warning light which illuminates just before clipping (distortion) occurs in
the output stage of the 306. This LED should never light or should only flash occasionally (on
peaks in the program material or page signal). If the CLIP LED stays on turn the GAIN control
counterclockwise until the LED extinguishes.
GAIN (dB) — The GAIN control is the final volume adjustment. Once you have achieved the desired
balance between page signal and program material use the GAIN control to determine the overall
output level of the 306. Turning this control clockwise increases the volume and turning this
control counterclockwise decreases the volume. To neither add nor subtract gain at this stage set
the GAIN control to the 12 o clock position (the unity gain position for this control).
POWER LED — This LED lights to indicate the presence of power at the POWER INPUT receptacle on
the rear of the 306.

306
6
Rear Panel Overview Chapter 5
OFF
LINE
ON
MIC
MIC/LINE
306
PREAMP/DUCKER
PHANTOM
PROGRAM INPUTS
RIGHT
LEFTRIGHT
PAGE INPUTPAGE MIX OUTPUTS
LEFT
RIGHT
RIGHT
DIRECT OUT
INPUT
POWER
SERVICABLE PARTS.
POWER SUPPLY ONLY.
SYMETRIX PS-3
CONNECT TO
SUPPLY ONLY.
OR PS-3E POWER
FABRIQUÉAUX E.-U. PAR SYMETRIX INC.,
WA, USA. THIS PRODUCT CONTAINS NO USER
MANUFACTURED BY SYMETRIX INC., LYNNWOOD
LYNNWOOD, WA, USA. RÉFÉREZ TOUTE
RÉPARATION ÀUN TECHNICIEN QUALIFIÉ.
POWER INPUT — This is a 7-pin DIN power receptacle. Connect only the Symetrix PS-3 (120V power
supply) Symetrix PS-3E (230V power supply) or Symetrix PS-3Y (power supply splitting cable for
powering two Symetrix units) to the POWER INPUT receptacle. Connect the AC power connector of
the PS-3 or PS-3E to an AC power source that is of the correct voltage and frequency as marked on
the PS-3 or PS-3E.
PAGE DIRECT OUT — This Euroblock terminal connector provides a line-level balanced output of
page signal only (no program material). The balanced output terminal pins are ground low (-) and
high (+). For unbalanced operation use the high (+) and ground terminal pins. Do not ground the
low (-) terminal pin. This output may be used to feed paging signal to another paging system.
MIX OUTPUT (RIGHT) — This output contains paging signal combined with the right channel of the
program material in the proportions determined by the setting of the MIX control on the front panel
of the 306. This line-level output is available at the RIGHT MIX OUTPUT Euroblock terminal connec-
tor (balanced) and at the RIGHT MIX OUTPUT RCA connector (unbalanced).
MIX OUTPUT (LEFT) — This output contains paging signal combined with the left channel of the
program material in the proportions determined by the setting of the MIX control on the front panel
of the 306. This line-level output is available at the LEFT MIX OUTPUT Euroblock terminal connector
(balanced) and at the LEFT MIX OUTPUT RCA connector (unbalanced).
PROGRAM INPUTS (RIGHT) — Connect the right channel of your line-level program source (signal to be
ducked) to either the RIGHT PROGRAM INPUT Euroblock connector (balanced) or the RIGHT PROGRAM
INPUT RCA connector (unbalanced).
PROGRAM INPUTS (LEFT) — Connect the left channel of your line-level program source (signal to be
ducked) to either the LEFT PROGRAM INPUT Euroblock connector (balanced) or the LEFT PROGRAM
INPUT RCA connector (unbalanced).
PAGE INPUT — Connect the paging source (the signal that will cause ducking of program material) to
this XLR balanced input. The XLR connector is wired Pin 1 — ground Pin 2 — high (+) and Pin 3
— low (-). Be sure to set the PHANTOM and MIC/LINE switches to the appropriate positions.
PHANTOM switch — Set this switch to the out (off) position unless your paging source is a con-
denser microphone which requires phantom power. If your paging source is a condenser micro-
phone which requires phantom power set this switch to the in (on) position.
MIC/LINE switch — Set this switch to the line position if your paging source is a line-level source
such as the output of a mic preamp. If your paging source is a mic-level source such as the output
of a microphone set this switch to the mic position to engage the 306 s microphone preamp.
PHANTOM
OFFON LINEMIC
PAGE INPUT
MIC/LINE
306
RIGHT
PREAMP/DUCKER
LEFTRIGHTRIGHT LEFT
MIX OUTPUTS PROGRAM INPUTS
DIRECT OUT
SERVICABLE PARTS.
POWER
SYMETRIX PS-3
CONNECT TO
INPUT
WA, USA. THIS PRODUCT CONTAINS NO USER
MANUFACTURED BY SYMETRIX INC., LYNNWOOD
PAGE
RIGHT
CAN BE USED
CONNECTION
EITHER TYPE
OR PS-3E POWER
SUPPLY ONLY.
LYNNWOOD, WA, USA. RÉFÉREZ TOUTE
RÉPARATION ÀUN TECHNICIEN QUALIFIÉ.
POWER SUPPLY ONLY.
FABRIQUÉAUX E.-U. PAR SYMETRIX INC.,
TO PAGE INPUT
ANOTHER 306
(LINE LEVEL) OF
PAGE MICROPHONE
SYSTEM
HOUSE SOUND
(SIGNAL THAT WILL BE DUCKED)
PROGRAM SOURCE

306
7
ApplicationsChapter 6
Foreground Music with Paging
OUTPUT
PWR
0
GAIN (dB)
-20
CLIP
PROGRAM
PAGE
RELEASE
2 Sec
.5 Sec 4 Sec
MIX
+20
DUCKER
HOLD
2 Sec
4 Sec
BYPASS .25 Sec-600
-20
-40
THRESHOLD (dBv) DEPTH (dB)
-30
PREAMP/
DUCKER
306
DUCK
This type of paging system is typically used in a restaurant or shopping mall. In these venues the
pages should be clearly heard but the transition between paging and music should not be too
obtrusive. In this case we recommend that you duck the background music by 10 — 20dB and use
a longer RELEASE setting to create a smooth transition from paging back into music. Also you
should set the threshold low enough to engage the ducker when a page is made but high enough
that the ducker is not falsely triggered by ambient noise present at the page mic.
Foreground Music/Paging with Emergency Override
OUTPUT
PWR
0
GAIN (dB)
-20
CLIP
PROGRAM
PAGE
RELEASE
2 Sec
.5 Sec 4 Sec
MIX
+20
DUCKER
HOLD
2 Sec
4 Sec
BYPASS .25 Sec-600
-20
-40
THRESHOLD (dBv) DEPTH (dB)
-30
PREAMP/
DUCKER
306
DUCK
If you have a foreground music or paging system that you wish to override in the case of an
emergency you will want the ducking action to be swift and thorough. Connect the foreground
music source or line-level paging system output to the PROGRAM INPUT(S) of the 306. Connect the
emergency paging source to the PAGE INPUT and set the MIC/LINE switch to the appropriate
position. Use a low threshold setting for increased sensitivity and set the DEPTH control com-
pletely counterclockwise for maximum ducking. We also recommend long HOLD and RELEASE
settings to prevent the program material from returning too quickly.
Paging in Multiple Paging Zones
AND MIC/LINE TO LINE
SET PHANTOM OFF
OFF
LINE
306
PREAMP/DUCKER
ON
MIC
PAGE INPUT
RIGHT LEFT
PROGRAM INPUTS
RIGHT
MIC/LINE
PHANTOM
LEFTRIGHT
DIRECT OUT
PAGE MIX OUTPUTS
RIGHT
POWER
INPUT
CONNECT TO
SERVICABLE PARTS.
SYMETRIX PS-3
LYNNWOOD, WA, USA. RÉFÉREZ TOUTE
RÉPARATION ÀUN TECHNICIEN QUALIFIÉ.
POWER SUPPLY ONLY.
OR PS-3E POWER
FABRIQUÉAUX E.-U. PAR SYMETRIX INC.,
SUPPLY ONLY.
INPUTS ON
TO PAGE LINE
ANOTHER 306
WA, USA. THIS PRODUCT CONTAINS NO USER
MANUFACTURED BY SYMETRIX INC., LYNNWOOD
SYSTEM
2ND SOUND
(SIGNAL THAT WILL BE DUCKED)
PROGRAM SOURCE FOR 2ND ZONE
CAN BE USED
EITHER TYPE
CONNECTION
PAGE MICROPHONE
(SIGNAL THAT WILL BE DUCKED)
MAIN PROGRAM SOURCE
SYSTEM
MAIN SOUND
CAN BE USED
CONNECTION
EITHER TYPE
OFF
LINE
ON
MIC
MIC/LINE
306
PREAMP/DUCKER
PHANTOM
PROGRAM INPUTS
RIGHT
LEFTRIGHT
PAGE INPUTPAGE MIX OUTPUTS
LEFT
RIGHT
RIGHT
DIRECT OUT
INPUT
POWER
SERVICABLE PARTS.
POWER SUPPLY ONLY.
SYMETRIX PS-3
CONNECT TO
SUPPLY ONLY.
OR PS-3E POWER
FABRIQUÉAUX E.-U. PAR SYMETRIX INC.,
WA, USA. THIS PRODUCT CONTAINS NO USER
MANUFACTURED BY SYMETRIX INC., LYNNWOOD
LYNNWOOD, WA, USA. RÉFÉREZ TOUTE
RÉPARATION ÀUN TECHNICIEN QUALIFIÉ.
Perhaps your installation requires one type of program material for one area (such as a lobby or
concourse) and a second type of program material for another area (such as a lounge) but the
same announcements need to be heard in both locations. This would call for two Symetrix 306 s.
Connect the paging source to the PAGE INPUT of the first 306 taking care to set the MIC/LINE switch
to the appropriate position. Then connect the desired program source to the Program Inputs of the
first 306. Using a short balanced shielded cable connect the PAGE DIRECT OUT of the first 306 to
the PAGE INPUT of the second 306. Set the MIC/LINE switch on the second 306 to the line posi-
tion and connect the appropriate program source to the PROGRAM INPUTS of the second 306.

306
8
To Duck or Mute Program Material without Passing Page Audio
OUTPUT
PWR
0
GAIN (dB)
-20
CLIP
PROGRAM
PAGE
RELEASE
2 Sec
.5 Sec 4 Sec
MIX
+20
DUCKER
HOLD
2 Sec
4 Sec
BYPASS .25 Sec-600
-20
-40
THRESHOLD (dBv) DEPTH (dB)
-30
PREAMP/
DUCKER
306
DUCK
Perhaps you have a small localized sound system that needs to be ducked when a page on a
separate paging system occurs but you don t want the page audio to appear at the outputs of the
localized sound system. An example of this might be a museum exhibit which has its own localized
sound system that needs to be ducked when a page occurs on the larger museum-wide paging
system. Connect the page signal from the separate paging system to the PAGE INPUT of the 306.
Set the MIX control completely clockwise (toward Program) and the page audio will cause ducking
but will not pass to the outputs of the 306. Adjust the amount of ducking with the Depth control.
Another example of this type of use may be seen when visiting a certain family-oriented pizza
restaurant chain. These restaurants feature a 15-minute animated show at the top of the hour
every hour and the rest of the time background music is played. The animated show has its own
sound system to focus attention on the show and the background music needs to be muted when
the animated show occurs. In this instance you would connect the background music to the
PROGRAM INPUTS of the 306. Then connect an audio feed from the animated show to the PAGE
INPUT of the 306 making sure to set the MIC/LINE switch to the proper position. Set the DEPTH
control completely counterclockwise and set the MIX control completely clockwise.
This type of system is also used in some large airports. Each gate has its own small localized
paging system on which flights arriving and leaving at that gate are announced and on which
background music may be played. A larger separate paging system services the entire airport. To
mute the small sound systems at each gate when an announcement is made on the larger airport-
wide paging system connect a line-level local paging signal to the PROGRAM INPUT(S) of the 306.
Connect an audio feed from the larger airport-wide paging system to the 306 s PAGE INPUT taking
care to set the MIC/LINE switch to the correct position. Then set the DEPTH control completely
counterclockwise and set the MIX control completely clockwise.

306
9
TroubleshootingChapter 7
The power ED does not light:
Are you using the correct Symetrix power supply for your location? For areas with 120V AC
power the Symetrix PS-3 is correct. For locales with 230V AC power the Symetrix PS-3E is the
correct power supply.
Check the power supply connections at the 306 and at the AC power source.
Is the AC power source actually providing power?
If after checking all of the above the 306 is not powering up correctly consult a qualified service
technician or the Symetrix factory.
There is no output signal:
Is the power LED on? If not see above.
Is the Output Gain control set at 0 or higher?
Check input and output cables and connections.
Determine that there really is signal coming from the paging source and the program material
source and that these signals are reaching the 306.
Is the Mic/Line switch on the Page Input set to the correct position for your paging source?
If you are connecting a condenser paging mic that does not have its own power supply to the Page
Input of the 306 is the Phantom switch set to the in position?
Try setting the Mix control to the 12 o clock position.
Is the Duck LED lit? If so try turning the Threshold control clockwise. If the Threshold control is
set counterclockwise the ducker could be triggered by ambient or other random noises present at
the page mic. Shorter Hold time and Release time settings may help also.
Distortion in the output signal:
Is the Clip LED on? If it is turn the Output Gain down.
Check your signal sources to make sure that the incoming signals are not already distorted before
they reach the 306.
Check your input signals. Are they overdriving any of the 306 s inputs? If so reduce the incom-
ing signal level.
Is the distortion occurring in both the paging signal and in the program material signal?
If the distortion is occurring only in the paging signal check your paging source. If your paging
source is line-level did you set the 306 s Mic/Line switch to the out position?
If the distortion is occurring only in the program material signal then you may be feeding the 306 a
program signal that is too hot.
Are you using the correct Symetrix power supply for your locale (PS-3 for 120V AC power PS-3E
for 230V AC power)?
No ducking is occurring:
Is the Depth control turned clockwise (bypass)? Try turning this control counterclockwise.
Is page signal reaching the 306? Do you hear the page?

306
10
Buzz in the output:
Check input and output connector wiring.
Check for ground loops between interconnected system equipment.
Are all system components on the same AC ground?
Noise (hiss):
Check input signal levels. The input may be too low in level. If so boost the incoming signal.
Check the setting of the Mic/Line switch for the 306 s Page Input. If the incoming page signal is
Mic level make sure that the Mic/Line Switch is set to the in position. If the incoming page
signal is Line level the Mic/Line switch must be set to the out position.
Are one or both of the input signals already noisy? Listen up stream from the 306 to determine
that you are feeding it clean signals.
The 306 doesn t respond properly:
Consult a qualified service technician or the Symetrix factory.

306
11
Architects and Engineers Specifications
The 306 preamp/ducker shall provide page-over-music capability. The unit shall occupy one-half
rack space (1/2U).
The page input shall have one female XLR balanced input. The page input shall have a rear-panel
pushbutton which shall engage the preamp circuitry to provide a low-impedance microphone input
or bypass the preamp circuitry to provide a high-impedance line input. The page input shall also
have a rear-panel pushbutton which shall apply +15V phantom power to the page input.
The preamp/ducker shall have left-channel and right- channel line-level program inputs accessible
by either one stereo pair of unbalanced RCA jacks or one pair of balanced Euroblock detachable
terminal connectors.
The 306 shall incorporate a priority ducking system. When audio is present at the page input the
signal present at the program inputs shall be ducked. There shall be a threshold control which
determines the minimum level of page audio that will trigger the ducking function. There shall also
be a duck LED which lights to indicate that ducking is occurring. A depth control shall set the
amount of ducking that occurs. There shall be a hold control that determines the amount of time
that ducking continues once the page signal has dropped below threshold. A release control shall
determine how quickly the program material returns to normal levels after the hold time.
The output section of the 306 shall incorporate a mix control which determines the ratio of page
signal to program signal and a gain control which controls the level of signal present at the mix
outputs. There shall be a clip LED which lights to indicate that output distortion is imminent. The
306 shall have left-channel and right-channel line-level outputs accessible by either one stereo pair
of unbalanced RCA jacks or one pair of balanced Euroblock detachable terminal connectors.
The 306 shall also have a page direct output which provides line-level page-only signal. This
balanced output shall have one Euroblock detachable terminal connector.
The preamp/ducker shall be a Symetrix Inc. model 306 Preamp/Ducker.
Specifications
Specifications
In the interest of continuous product improvement, Symetrix, Inc. reserves the right to alter, change, or modify these specifications without prior
notice.
©1999,Symetrix,Inc. All rightsreserved.
Input/Output
Maximum Input Level +20dBu Balanced, +20dBu Unbalanced
Program Input Impedance >20kOhms Balanced,
>10k Ohms Unbalanced
Input Common Mode rejection >40dB, mic and line inputs
Microphone Phantom Power +15V
Maximum Output Level +26dBu Balanced (20k Ohm load)
+22dBm Balanced (600 Ohm load)
Output Impedance 400OhmsBalanced,200 OhmsUnbalanced
Performance Data
PageFrequencyResponse 50Hz to 15kHz, +0, -1 dB
ProgramFrequencyResponse 20Hz to 20kHz, +0, -1dB
PagePathTHD+Noise <.02% (Mic input to direct page output,
150 Ohm source)
ProgramPathTHD+Noise <.025% (+4dBu in, +4dBu out,
0dB ducking)
Output Gain +/-20dB
Chapter 8
Connections
Page Input XLR
Program Inputs RCAjacks,Euroblock
Mix Outputs RCAjacks,Euroblock
Page Direct Output Euroblock
PowerIn 7pinDIN
Physical
Size(hwd) ˚ rack unit
1.75 x 8.5 x 6.5 in., 4.445 x 21.59 x 15.875 cm.
Shipping Weight 4.5 lbs
Electrical
PowerRequirements 120V nominal, 95 to 130V AC,
50 to 60 Hz, 10 watts
230V nominal, 207 to 253V AC, 50 Hz, 10 watts

306
12
Block Diagram Chapter 9
MIX
GAIN
THRESHOLD
DEPTH
HOLD
RELEASE
UNBALANCED
BALANCED
RIGHT
RIGHT
PROGRAM IN
PROGRAM IN
UNBALANCED
PROGRAM IN
PROGRAM IN
BALANCED
LEFT
LEFT BALANCED
MIX OUT
LEFT
MIX OUT
BALANCED
RIGHT
MIX OUT
UNBALANCED
RIGHT
OUTPUT
PAGE
DIRECT
MIX OUT
UNBALANCED
LEFT
CLIP
DUCK
INPUT
PAGE
PHANTOM MIC/LINE
+V
VCA
VCA
CONTROL
VOLTAGE
CIRCUITRY

306
13
Warranty & Service
Symetrix Inc. expressly warrants that the product will be free from defects in material and workman-
ship for one (1) year. Symetrix’s obligations under this warranty will be limited to repairing or
replacing at Symetrix’s option the part or parts of the product which prove defective in
material or workmanship within one (1) year from date of purchase provided that the Buyer
gives Symetrix prompt notice of any defect or failure and satisfactory proof thereof. Products
may be returned by Buyer only after a Return Authorization number (RA) has been obtained
from Symetrix. Buyer will prepay all freight charges to return the product to the Symetrix
factory. Symetrix reserves the right to inspect any products which may be the subject of any
warranty claim before repair or replacement is carried out. Symetrix may at its option require
proof of the original date of purchase (dated copy of original retail dealer’s invoice). Final
determination of warranty coverage lies solely with Symetrix. Products repaired under warranty
will be returned freight prepaid by Symetrix via United Parcel Service (surface) to any location
within the Continental United States. At Buyer’s request the shipment may be returned via
airfreight at Buyer’s expense. Outside the Continental United States products will be returned
freight collect.
The foregoing warranties are in lieu of all other warranties, whether oral, written, express,
implied or statutory. Symetrix, Inc. expressly disclaims any IMP IED warranties, including
fitness for a particular purpose or merchantability. Symetrix’s warranty obligation and
buyer’s remedies hereunder are SO E Y and exclusively as stated herein.
This Symetrix product is designed and manufactured for use in professional and studio audio
systems and is not intended for other usage. With respect to products purchased by consum-
ers for personal family or household use Symetrix expressly disclaims all implied warran-
ties, including but not limited to warranties of merchantability and fitness for a particular
purpose.
This limited warranty with all terms conditions and disclaimers set forth herein shall extend
to the original purchaser and anyone who purchases the product within the specified warranty
period.
Warranty Registration must be completed and mailed to Symetrix within thirty (30) days of the
date of purchase.
Symetrix does not authorize any third party including any dealer or sales representative to
assume any liability or make any additional warranties or representation regarding this product
information on behalf of Symetrix.
This limited warranty gives the buyer certain rights. You may have additional rights provided
by applicable law.
306 Limited Warranty
Limitation of Liability
The total liability of Symetrix on any claim whether in contract tort (including negligence) or
otherwise arising out of connected with or resulting from the manufacture sale delivery
resale repair replacement or use of any product will not exceed the price allocable to the
product or any part thereof which gives rise to the claim. In no event will Symetrix be liable for
any incidental or consequential damages including but not limited to damage for loss of
revenue cost of capital claims of customers for service interruptions or failure to supply and
costs and expenses incurred in connection with labor overhead transportation installation or
removal of products or substitute facilities or supply houses.
Chapter 10

306
14
If you have determined that your 301 requires repair services and you live outside of the
United States please contact your local Symetrix dealer or distributor for instructions on how
to obtain service. If you reside in the U.S. then proceed as follows:
Before sending anything to Symetrix contact our Customer Service Department for a return
authorization (RA) number. The telephone number is [phone] or email:
[email protected]
In-warranty Repairs
To get your 301 repaired under the terms of the warranty:
1. Call us for an RA number.
2. Pack the unit in its original packaging materials.
3. Include your name address daytime telephone number and a brief
statement of the problem.
4. Write the RA number on the outside of the box.
5. Ship the unit to Symetrix freight prepaid.
We do not accept freight collect shipments.
Repairs made in-warranty will cost you only one-way freight charges. We ll prepay the return
(surface) freight.
If you send us your product in substandard packaging we will charge you for factory ship-
ping materials. If you don t have the factory packaging materials please use an oversized
carton wrap the unit in a plastic bag and surround it with bubble-wrap. Pack the box full of
Styrofoam peanuts. Be sure there is enough clearance in the carton to protect the rack ears
(you wouldn t believe how many units are returned with bent ears). We will return the unit in
Symetrix packaging. Of course if the repair is due to operator error parts and labor will be
charged. In any event if there are charges for the repair costs you will pay for the return
freight. All charges will be COD unless you have made other arrangements (prepaid Visa or
Mastercard).
Out-of-warranty Repairs
If the warranty period has passed you ll be billed for all necessary parts labor packaging
materials and freight charges. Please remember you must call for an RA number before
sending the unit to Symetrix.
Servicing the 306

306
15
Declaration of ConformityChapter 11
Declaration of Conformity
We Symetrix Incorporated
6408 216th St. SW Mountlake Terrace Washington USA
declare under our sole responsibility that the product:
306 Preamp/Ducker
to which this declaration relates
is in conformity with the following standards:
EN 60065
Safety requirements for mains operated electronic and related
apparatus for household and similar general use.
EN 55103-1
Electromagnetic compatibility - Generic emission standard
Part 1: Residential, commercial, and light industry.
EN 55103-2
Electromagnetic compatibility - Generic immunity standard
Part 1: Residential, commercial, and light industry.
The technical construction file is maintained at:
Symetrix, Inc.
6408 216th St. SW
Mountlake Terrace WA 98043
USA
The authorized representative located within the European Community is:
World Marketing Associates
P.O. Box 100
St. Austell Cornwall PL26 6YU U.K.
Date of issue: April 30 1999
Place of issue:Mountlake Terrace Washington USA
Authorized signature:
Dane Butcher President Symetrix Incorporated.

306

306

306
20
Symetrix, Inc.
6408 216th St. SW
Mountlake Terrace WA 98043
USA
Tel: [phone]
Fax: [phone]
Website: http://www.symetrixaudio.com
Email: [email protected]