Symetrix 305 User manual

305 Distribution Amplifier (1x4)
User s Guide
305

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 Connecting to Other Gear 7
Chapter 7 Signal Flow Chart 10
Chapter 8 Troubleshooting 11
Chapter 9 Specifications 12
Chapter 10 Warranty and Service 13
Chapter 11 Declaration of Conformity 1
Rev A, 1 June, 1998
Symetrix part number 330 -0A00
Subject to change at our whim and fancy without
notice.
'1998, 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 photo-
copying, 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]
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IntroductionChapter 1
Front panel
Rear panel
PWR
DCB
OUTPUTS
A
CLIP
INPUT
+10
0
-10
305
DISTRIBUTION
AMPLIFIER (1x4)
ABCD OUTPUT INPUT
INPUT
POWER
SUPPLY ONLY.
CONNECT TO
SYMETRIX PS-3
OR PS-3E POWER
THIS PRODUCT CONTAINS NO USER SERVICABLE PARTS.
MANUFACTURED BY SYMETRIX INC. LYNNWOOD, WA USA
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.
RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.
Congratulations on your purchase of the
Symetrix 305 Distribution Amplifier (1x4) The
305 accepts one balanced input signal and
distributes it to four independent outputs The
volume of the input may be controlled via a
front panel trimpot, as can the volume of each
individual output
Distribution amplifiers are generally used to
split one signal into multiple isolated sends
For example, a sound reinforcement engineer
may wish to supply the mixer s mono output
signal to the house sound system, to a
backstage cueing system, to a DAT recorder
and to a media feed The Symetrix 305 fits the
bill nicely, supplying four separate, isolated
outputs In the event that one of the outputs
shorts (for example, the TV camera operator
inadvertently plugs a shorted cord into the
media feed), the other three outputs continue
to supply signal, unaffected by the short
circuit The outputs are also isolated to
protect against ground hum problems
The 305 s input level control allows the sound
engineer to adjust the 305 s input level
properly for the amount of signal being fed to
it from the mixer s output The individual
output level trimpots allow each of the four
output levels to be tailored to their application
For example, an output that is being fed to the
input of a DAT recorder may be adjusted to
provide a signal level that optimizes recording
resolution without overloading the input of the
DAT recorder
The Symetrix 305 also offers a four-LED input
level meter, to assist the user in setting
optimum operating levels The balanced input
stage is designed for high common mode
rejection and RF immunity Output line drivers
are stable, short-circuit protected, and de-
signed around industry standard 5532-type op
amps
The Symetrix 305 offers high-quality, low-noise
audio distribution with convenient and
desirable features, all at a modest price Only
minimal space in your equipment rack is needed
to contain this powerhouse unit
We recommend that you read this manual
cover-to-cover You will find the answers to
most of your questions inside However, if you
are in a hurry, go directly to Chapter 3 (Fast
Setup) It will get you started quickly Please
feel free to contact us if you have questions,
comments or suggestions
Phone:[phone]
Fax:[phone]
Email: symetrix@symetrixaudio com
Website: www symetrixaudio com

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The information in this summary is intended
for persons who operate the equipment as well
as repair personnel Specific warnings and
cautions are found throughout this manual
wherever they may apply
The notational conventions used in this
manual and on the equipment itself are
described in the following paragraphs
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 per-
sons
The exclamation point within an equilateral
triangle is intended to alert the user of the
presence of important operating and mainte-
nance (servicing) instructions in the literature
accompanying the 305 (i e this manual)
Caution To prevent electric shock, do not
use the polarized plug supplied
with the 305 with any extension
cord, receptacle, or other outlet
unless the blades can be fully
inserted.
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 305
Equipment Markings
Operator Safety Summary Chapter 2
Caution Identifies infor ation that, if not
heeded, ay cause da age to the
305 or other equip ent in your
syste .
Warning Identifies information that, if
ignored, may be hazardous to
your health or that of others.
CAPITALS Controls, switches or other
markings on the 305 s chassis
Boldface Strong emphasis
Power source - This product is intended to
operate from a power source that does not
apply more than 255Vrms between the power
supply conductors or between either power
supply conductor and ground A protective
ground connection, by way of the grounding
conductor in the power cord, is essential for
safe operation
Danger from loss of ground - If the protective
ground connection is lost, all accessible
conductive parts, including knobs and
controls that may appear to be insulated, can
render an electric shock
In-line power supply - This product receives its
operating power from the Symetrix PS-3 DC
power supply This is the only power supply
approved for use with the product Do not
connect the product to any other in-line, or
plug-in, transformer The use of other power
sources may cause damage to the equipment
or present a shock hazard to the operator
Operating location - Do not operate this
equipment under any of the following condi-
tions: explosive atmospheres, in wet locations,
in inclement weather, improper or unknown AC
mains voltage, or if improperly fused
tay out of the box - To avoid personal injury
or injury to others, do not remove the product
covers or panels Do not operate the product
without the covers and panels properly
installed
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

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Fast First-Time Setup
Follow these instructions to get your 305 up-and-running as quickly as possible The intent of this
section is fast setup Refer to later chapters for explanation of the 305 s controls and functions
Connect audio inputs and outputs If you do not know how to do this, forget Fast Set-Up
and read Chapter 5
Set INPUT level trim control straight up (12 o clock position)
Set OUTPUT level trim controls at maximum level (clockwise rotation)
Plug the 305 into an AC outlet using the external power supply
Caution:Failure to connect the 305 to the proper AC ains voltage ay
cause fire and/or internal da age.
Warning: Lethal voltages are present inside the chassis. There are no user
serviceable parts inside the chassis. Refer all service to qualified
service personnel or to the factory.
Apply line level audio signal to the input Line level means previously amplified
audio, i e not the output of a microphone or other unamplified audio transducer
Turn up the INPUT level pot until the red CLIP LED just barely lights Then back the
level down just a bit until the CLIP LED doesn t come on any more, or only occasionally
flashes
Now read the rest of this user s guide



≠



Fast Setup
Chapter 3



◊



⌫⌫
⌫⌫
⌫

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Input Level Controls
The input level control on the 305 is marked INPUT This control adjusts it s corresponding input
signal over a 30dB range With signal applied to input, turn up the INPUT level pot until the red
CLIP LED just barely lights Then back the level down just a bit until the CLIP LED doesn t come
on any more, or only occasionally flashes This is the optimum setting and will provide the greatest
signal-to-noise ratio without distortion
If your incoming signal position is unpredictable then we suggest a straight up (12 o clock)
setting Since the 305 s input has 18dB of headroom above +4dBu, this setting should work well
under most conditions
Note If you wish to even out the variances in signal level, we recommend processing your
signal with the Symetrix 421m Automatic Leveler before it reaches the 305
If you find that your input signal is very low (the output of a -10 consumer level device, such as
a CD player, for example), turn the INPUT level control clockwise to boost the signal Conversely,
if you’re feeding a +8 broadcast level signal to the 305 then turn the INPUT level control counter-
clockwise until the proper LED display is achieved
Output Level Controls
The four output level controls on the 305 are in the section marked OUTPUT and are labeled
A , B , C , and D Use these controls to attenuate the output level over a 20dB range Start
by turning all controls fully clockwise (unity gain) This will create equal levels from all outputs If
for some reason you wish to reduce the level of certain outputs then turn the appropriate control(s)
counterclockwise Otherwise, for better overall system performance, it s best to leave the controls
wide open (full clockwise) for the hottest possible output signals
Front Panel Overview Chapter 4
Front panel drawing
PWR
DCB
OUTPUTS
A
CLIP
INPUT
+10
0
-10
305
DISTRIBUTION
AMPLIFIER (1x4)

305
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Rear Panel OverviewChapter 5
The 305 is fitted with removable terminal blocks for both input and output connections While not
absolutely necessary, it is usually much easier to unplug the removable block before making or
changing connections
INPUT
The 305 s input is balanced Of course, it may be used in unbalanced configurations, but for
optimum system wide performance (best noise rejection) balanced operation is highly recom-
mended whenever possible Be sure to use shielded cable for both input and output connections
The wire should always be two-conductor plus shield, even for unbalanced connections
For a balanced input signal:
1 Connect the incoming signal + (high) to the + INPUT terminal of the 305
2 Connect the incoming signal - (low) to the - INPUT terminal of the 305
3 Connect the incoming signal ground (shield) to the ground terminal of the 305 Repeat
for all inputs
For an unbalanced input signal, using two-conductor shielded cables:
1 Connect the incoming signal + (high) to the + INPUT terminal of the 305 Use
the red wire
2 Connect the incoming signal ground to the - INPUT terminal of the 305 Use the
black wire
3 Connect the cable shield at the ground connection of the 305 only
If you experience hum or noise, make sure that both the 305 and the device which you are feeding
to the 305 s input are grounded on the same AC mains circuit If this is not the source of the noise
problem, you must isolate the unbalanced output from the balanced input with an audio trans-
former or matchbox
If the unbalanced output of the device preceding the 305 is -10dBV (semi-pro or consumer level),
the Symetrix 303 Interface Amplifier is an excellent choice for isolation Not only will the 303
convert the unbalanced signal to an isolated balanced signal, it will also boost the -10dBV signal to
the +4dBu level at which the 305 was designed to operate
OUTPUTS
The 305 s output is an active balanced circuit and should be used to feed balanced audio inputs
Use two-conductor shielded audio cable for all connections
Feeding balanced inputs:
1 Connect the + (high) OUTPUT terminal of the 305 to the + (high) of the input
of the device which you are feeding
2 Connect the - (low) OUTPUT terminal of the 305 to the - (low) of the input of
the device which you are feeding
3 Connect cable shield to the ground of the 305 and the ground connection of the
device which you are feeding
ABCD OUTPUT INPUT
INPUT
POWER
SUPPLY ONLY.
CONNECT TO
SYMETRIX PS-3
OR PS-3E POWER
THIS PRODUCT CONTAINS NO USER SERVICABLE PARTS.
MANUFACTURED BY SYMETRIX INC. LYNNWOOD, WA USA
FABRIQUÉAUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.
RÉFÉREZ TOUTE RÉPARATION ÀUN TECHNICIEN QUALIFIÉ.
Rear panel drawing

305
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Feeding unbalanced inputs:
WE DON’T RECOMMEND IT. If you must feed an unbalanced input with the 305, you should
isolate the two devices with either an audio transformer or an interface matching device (a match-
box ) The 305 follows the AES standards for balanced audio circuits The ground connections of
the amplifier are chassis ground
If you must connect the output of the 305 directly to an unbalanced input, try this procedure Use
two-conductor shielded audio cable
1 Connect the + (high) OUTPUT terminal of the 305 to the + (high) of the
unbalanced input
2 Make no connection to the - (low) OUTPUT terminal of the 305
3 Connect the cable shield at the 305 s ground and at the input connector of the
unbalanced input
The output signal level of the 305 will be 6 dB lower when driving an unbalanced input without a
transformer or matching interface device
If you experience hum or noise, make sure that both the 305 and the device which you are feeding
are grounded on the same AC mains circuit If this is not the source of the noise problem, you must
isolate the balanced output from the unbalanced input with an audio transformer or matchbox

305
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Connecting to Other GearChapter 6
Matching Levels vs Matching Impedances
In any audio equipment application, the question of matching inevitably comes up Without
digging a hole any deeper than absolutely necessary, we offer the following discussion to (hope-
fully) clarify your understanding of the subject
Over the years, we have all had impedance matching pounded into our heads This is important
only for vintage audio systems, power amplifiers, and RF Technically speaking, the reason is
power transfer, which reaches a maximum when source and load are matched Modern audio
systems are voltage transmission systems and source and load matching is not only unnecessary,
but undesirable as well
Vintage audio systems operate at 600 ohms (or some other impedance value), and must be
matched, both at their inputs and at their outputs Generally speaking, if you are dealing
with equipment that uses vacuum tubes, or was designed prior to 1970, you should be
concerned about matching These units were designed when audio systems were based on
maximum power transfer, hence the need for input/output matching
Power amplifiers are fussy because an abnormally low load impedance generally means a
visit to the amp hospital Thus, it s important to know what the total impedance of the pile
of speakers connected to the amplifier really is
RF systems are matched because we really are concerned with maximum power transfer
and with matching the impedance of the transmission line (keeps nasty things from
happening) Video signals (composite, baseband, or otherwise) should be treated like RF
Some folks seem to believe that balanced/unbalanced lines and impedances are related; or even
worse that they are associated with a particular type of connector Not so Unbalanced signals are
not necessarily high-impedance and balanced signals/lines are not necessarily low-impedance
Similarly, although 1/4 inch jacks are typically used for things like guitars (which are high-imped-
ance and unbalanced), this does not predispose them to this use alone After all, 1/4 inch jacks are
sometimes used for loudspeakers, which are anything but high-impedance Therefore, the presence
of 3-pin XLR connectors should not be construed to mean that the input or output is low-imped-
ance (or high-impedance) The same applies to 1/4 inch jacks
So, what is really important? Signal level, and (to a much lesser degree), the impedance relation
between an output (signal source) and the input that it connects to (signal receiver)
Signal level is very important Mismatch causes either loss of headroom or loss of signal-to-noise ratio
Thus, microphone inputs should only see signals originating from a microphone, a direct (DI) box, or an
output designated microphone-level output Electrically, this is in the range of approximately -70 to -20
dBm Line inputs should only see signals in the -10 to +24 dBm/dBu range Guitars, high-impedance
microphones, and many electronic keyboards do not qualify as line-level sources
The impedance relation between outputs and inputs needs to be considered, but only in the
following way - Always ake sure that a device s input i pedance is higher than the output
source i pedance of the device that drives it
Some manufacturers state a relatively high-impedance figure as the output impedance of their
equipment What they really mean is that this is the minimum load impedance that they would like
their gear to see In most cases, seeing a output impedance figure of 10,000 (10K) ohms or higher
from modern equipment that requires power (batteries or AC) is an instance of this type of rating If
so, then the input impedance of the succeeding input must be equal to or greater than the output
impedance of the driving device
Symetrix equipment inputs are designed to bridge the output of whatever device drives the input
(i e to be greater than 10 times the actual source impedance) Symetrix equipment outputs are
designed to drive 600-ohm or higher loads (600-ohm loads are an archaic practice that won t go
away) You don t need to terminate the output with a 600-ohm resistor if you aren t driving a 600-
ohm load (If you don t understand the concept of termination, you probably don t need to
anyway )

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The two facts that you need to derive from this discussion are:
Match signal levels for best headroom and signal-to-noise ratio
For audio, impedance matching is only needed for vintage equipment and power amplifier
outputs In all other cases, ensure that your inputs bridge your outputs (meaning the
inputs are in the range of 2 to 200 times the output source impedance)
Signal Levels
The 305 is designed around studio/professional line levels: +4 dBu or 1 23 volts RMS The unit is
quiet enough to operate at lower signal levels such as those found in semi-pro or musical instru-
ment (MI) equipment (-10 dBv or 300 millivolts)
I/O Impedances
The 305 is designed to interface into almost any recording studio or sound reinforcement applica-
tion This includes:
600-ohm systems where input and output impedances are matched
Modern bridging systems where inputs bridge and outputs are low source impedances
(voltage transmission systems)
The 305 s input impedance is 20-kilohms balanced The inputs may be driven from any balanced
source capable of delivering at least -10 dBv into the aforementioned impedances
The 305 s output impedance is 200 ohms balanced, 100 ohms unbalanced The output line driver
delivers +22 dBu into 600-ohm balanced loads or +18 dBm into 600-ohm unbalanced loads
Input and Output Connections
The illustration on the next page shows how to connect the 305 to balanced and unbalanced
sources and loads Please remember that unbalanced operation is not recommended
If you must operate the 305 from unbalanced sources, run a 2-conductor shielded cable (that s two
conductors plus the shield) from the source to the 305 At the source, connect the cable
connector s sleeve to one conductor (this will be the - or the low conductor) and connect the
tip to the remaining + or high conductor, leaving the shield unconnected Connect the shield
to the chassis connection and the cable s - and + to the corresponding 305 input connection
This is the preferred method as it makes best use of the 305 s balanced input (even though the
source is unbalanced) An alternative shown in the illustration converts the 305 s balanced input
into an unbalanced input at the input connector This works, but is more susceptible to hum and
buzz than the preferred method There is no level difference between methods
You can drive unbalanced loads with the 305 s outputs by using the XLR connector with pin 3 left
open In an emergency (the show must go on), you can ground pin 3, but if you have the
choice leave it open If you must ground pin 3, it must be grounded at the 305, rather than at the
other end of the cable The price, regardless of whether or not pin 3 is grounded is 6 dB less output
level If your system is wired with pin 3 hot, and you are driving an unbalanced load, pin 2 must
float