Symetrix 307 User manual

307 Dual Isolation Transformer
Users Guide
307

i
Table of Contents
Chapter 1 Introduction 1
Chapter 2 Operator Safety Summary 2
Chapter 3 Fast Setup 3
Chapter 4 Front & Rear Panel Overview 4
Chapter 5 Applications 5
Chapter 6 Troubleshooting 6
Chapter 7 Specifications 7
Chapter 8 Warranty and Service 8
Appendix 1 Wiring Diagram 10
Chapter 9 Declaration of Conformity 11
Rev A, 15 October, 1998
Symetrix part number 53307-0A00
Subject to change 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.
14926 35th Ave.West
Lynnwood, WA 98037 USA
Tel [phone]
Fax [phone]
Email: [email protected]
307

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IntroductionChapter 1
Front panel
Rear panel
Congratulations on your purchase of the
Symetrix 307 Dual Isolation Transformer. The
307 is a two-channel isolation transformer
intended for use in solving interface problems
which require galvanic isolation between
source and load. The 307 provides two high-
quality line isolation transformers in a conve-
nient half-rack enclosure.
Transformers have a bad reputation in modern
audio systems. Years ago, everything was
transformer coupled; mostly because that was
the only way to couple a tube to a 600-ohm
load. Of course, tubes are now an alternative
amplification device, and most solid-state units
are direct coupled to the load, be it 600-ohms
or an open circuit. By doing away with
transformers, weve extended the bandwidth
and lowered the distortion of our systems.
Unfortunately, weve also made our systems
more susceptible to circulating ground cur-
rents. For ground-isolation problems, espe-
cially those that involve circulating currents in
the ground system, a transformer is the
preferred method of solving the problem.
Another use for a transformer is connecting
balanced outputs with unbalanced inputs. Most
transformerless outputs emulate a grounded
center-tapped transformer. This puts half the
output voltage swing on pin 2 and half on pin
3. For unbalanced loads, you generally ignore
one of the two signals, which is fine, but it just
cost you 6 dB in output level. Going through a
patchbay is even more difficult, as you want
both output pins for a balanced load, and you
want to be able to float pin 3 for unbalanced
loads. In most patch bays, this is difficult or
impossible. A transformer between the bal-
anced output and the patchbay solves this
neatly. You can ground either side for driving
unbalanced loads and everything works as
planned. Life is grand.
The 307s inputs and outputs use Euroblock
connectors which accept bare wires (screw
terminals with a twist). Separate connections
are provided for each internal circuit ground as
well as the chassis. Each channel also has a
ground lift switch that allows easy separation
of the input and output ground systems. The
307 operates at +4dBu signal levels.
We recommend that you read this manual from
cover to cover. Somewhere between the
confines of the two covers you should find the
answers to most (98%) of your questions. If
youre in a hurry (like most of us) skip ahead
to Section 3, Fast Setup. This section will
help you get connected, and send you on your
way.
Should you have any comments or questions,
please do not hesitate to contact us. Your calls
and e-mail are always welcome.
Phone: [phone]
Fax: [phone]
Email: [email protected]
Website: www.symetrixaudio.com
LIFT
GROUND
CONNECT
LIFT
GROUND
CONNECT
307
DUAL ISOLATION
TRANSFORMER
CHANNEL 2CHANNEL 1
CHANNEL 1INPUTCHANNEL 2
CH1 OUTPUTINPUTOUTPUT CH2
GROUND
INPUT
DUAL ISOLATION TRANSFORMER 307
RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.
MANUFACTURED BY SYMETRIX INC. LYNNWOOD, WA USA
THIS PRODUCT CONTAINS NO USER SERVICABLE PARTS.

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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 persons.
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 307 (i.e. this manual).
Note The 307 is a completely passive
device and there is no AC power (or
DC power for that matter) inside the
enclosure. Consequently there is no
shock hazard involved in the equip-
ment itself. If the equipment used with
the 307 is not grounded properly or is
improperly connected to the AC line,
then the possibility of a shock hazard
becomes quite real.
Caution To prevent electric shock, do not use
the polarized plug supplied with your
pieces of audio equipment with any
extension cord, receptacle, or other
outlet unless the blades can be fully
inserted to prevent blade exposure.
Equipment Markings
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 307.
Caution Identifies information that, if not
heeded, may cause damage to the
307 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 307s chassis.
Boldface Strong emphasis.
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.
Stay 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
N
o 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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This section discusses a variety of topics, all related to getting signals in and out of the 307 and
getting on with using it.
I/O Connections
All input and output connections use screw-type connectors. The connectors are modular and may
be detached from the unit for installation or for servicing. These connectors are designed for use
with bare wire; tinning is not necessary for stranded conductors.
Connect your sources to the rear-panel input connectors. These connectors may be driven from a
balanced or unbalanced, low-impedance source. When using an unbalanced source, you can
connect the output minus terminal to ground either at the source or at the 307.
Connect the outputs as required. These connectors deliver a floating balanced output signal. For
unbalanced use, connect the output minus terminal to circuit ground at the 307 or at the load. For
unbalanced output use, you may want to ignore circuit ground and just use the plus and minus
terminals. In this way, the two ground systems are completely isolated.
[See Appendix 1 on page 10.]
Fast Setup
Chapter 3
Grounding
You have several options:
1. Connect the source and load ground systems together.
2. Separate the source and load ground systems.
3. Connect circuit ground and chassis ground together.
4. Separate circuit ground and chassis ground.
The number one consideration for each of these decisions is whether or not your system hums
when the grounds are connected together.
Source Impedance
The Achilles heel of any transformer is high levels at low frequencies. The transformers in the 307
perform best when driven from a low source impedance, preferably 150-ohms or less.
When driven from a 600-ohm source, the 307's performance is still quite acceptable and it im-
proves when the transformers secondary winding is terminated in 600 ohms.
The difference between 50-ohms source impedance and 600-ohms source impedance is:
50-ohm source, 0 dBu, 20Hz THD+N < .5%.
600-ohm source, 0 dBu, 20Hz THD+N < 1%

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Front & Rear Panel Overview Chapter 4
LIFT
GROUND
CONNECT
LIFT
GROUND
CONNECT
307
DUAL ISOLATION
TRANSFORMER
CHANNEL 2CHANNEL 1
CHANNEL 1INPUTCHANNEL 2
CH1 OUTPUTINPUTOUTPUT CH2
GROUND
INPUT
DUAL ISOLATION TRANSFORMER 307
RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.
MANUFACTURED BY SYMETRIX INC. LYNNWOOD, WA USA
THIS PRODUCT CONTAINS NO USER SERVICABLE PARTS.
GROUND switches Push switches (one per channel) that separate the input and output
ground systems from each other.
CHANNEL 1 & 2 Each input and output has three connections: circuit common (shown as
connections a ground symbol), minus and plus audio connections.
All of the circuit common symbols are connected together when the front-panel ground switch is
set to the CONNECT (in) position. When the ground switch is set to the LIFT (out) position, the input
and output ground systems are separate.
The input terminals are designed to be driven from a low-impedance source, 600-ohms or less
(preferably less). Note that the source impedance is generally much lower than the minimum rated
load impedance for an output.
INPUT GROUND The input ground connections are also available in this block. You can
use the extra connections to connect the input ground to the chassis
ground.
The chassis ground connection uses a different sort of ground symbol. It connects to the metal
enclosure that surrounds the unit.

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ApplicationsChapter 5
Converting an Unbalanced Source
In this application, the 307 balances the
output of an unbalanced source by
mirroring the impedance of the load back
to the source. For this reason, it is impor-
tant that the 307 be driven from a low
source impedance, preferably less than
600 ohms. This means that the 307 should
not be used as a direct box. The Figure to
the right shows the connections. Start with
the GROUND LIFT switches in the in
position, and lift the ground only if
necessary.
Isolating the Ground Systems
In this application, the ground systems
on each side of the 307 are not compat-
ible. This means that when you try to
interconnect them, the usual result is
hum. In the past, it was fairly common-
place to simply lift the power line ground
of one of the pieces of equipment, and
this was often sufficient to quiet the
system. For safety reasons, this is very
poor practice, and an audio isolation
transformer such as the 307 is a much
better solution. The Figure to the right
shows the connections. Ensure that the
GROUND LIFT switches are in the LIFT
position.
CH1
INPUT
OUTPUTINPUTOUTPUT
CHANNEL 2
CH2
GROUND CHANNEL 1
INPUT
CHANNEL 1
INPUTCH1INPUT
GROUND
CH2
INPUT
OUTPUTOUTPUT
CHANNEL 2
Driving an Unbalanced Load
In this application, the source is elec-
tronically balanced and the load is
unbalanced, and there is a fair amount of
cable between them. For a variety of
reasons, it is impractical to float the low
side of the source when driving this load.
Another reason is that the load is off
somewhere in the building, and simply
bringing the unbalanced input back to
the source is likely to cause hum.
Here we use the 307 to derive a floating
output signal that is free of the ground
system. You can locate the unit either at
the source or at the load. In most cases,
locating it at the load is probably better. The Figure above shows the connections. Since were
ignoring the output ground connections, the setting of the GROUND LIFT switches is immaterial.
CHANNEL 1
CH1 OUTPUT
CHANNEL 2
INPUTOUTPUT CH2
INPUT
GROUND
INPUT

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Troubleshooting Chapter 6
Troubleshooting Chart
SYMPTOM PROBABLE CAUSE
Hum or buzz in output Check input and output connector wiring. Ground loop: check related
system equipment grounding. Are all system components on the same
AC ground? Is the 307 in close proximity to a large hum field (such as a
power amp)?
Distortion Check input signal. Is it too hot, or is it already distorted? Check the
output loading. It should be above 600 ohms. Is the input of the device
following the 307 clipping? Is the input of the device following the 307
a line-level input (it should be)? Is something else clipping?

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Architects and Engineers Specifications
SpecificationsChapter 7
Specifications
In the interest of continuous product improvement, Symetrix, Inc.
reserves the right to alter, change, or modify these specifications
without prior notice.
©1998, Symetrix, Inc. All rights reserved.
Input/Output
Maximum Input Level +22dBu Balanced
CMRR >80dB @ 60Hz
Performance Data
Frequency Response 20Hz to 20kHz, +/-0.5dB
THD <.07%, 50Hz at 21dBu,
low-Z input, high-Z load
Insertion Loss <3dB, 600 Ohm load
Connections
Input Euroblock
Output Euroblock
Physical
Size (hwd) ½ 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
No Power Requirements
The transformer isolation box shall be a two channel model that offers hum and noise elimination,
and grounding solutions for audio equipment interconnection. The unit shall occupy one-half rack
space (1/2 rack).
There shall be one ground lift switch per channel on the front panel that connects or disconnects
the input ground to the output ground. The rear panel shall offer all input and output connections
on removable euro-block style screw terminal connectors. There shall also be terminals to allow
the user to connect circuit ground to chassis ground.
Total Harmonic Distortion shall be no greater than 0.07% (50Hz at 21dBu, low-Z input, high-Z
load). The unit shall be a completely passive device and require no power, AC or battery, for
operation.
The unit shall be a Symetrix 307 Dual Isolation Transformer.

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Warranty and Service Chapter 8
Symetrix, Inc. expressly warrants that the product
will be free from defects in material and
workmanship 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,
307 Limited Warranty
Limitation of Liability
The total liability of Symetrix on any claim,
whether in contract, tort (including negli-
gence) 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
Inc. expressly disclaims any IMPLIED
warranties, including fitness for a par-
ticular purpose or merchantability.
Symetrix's warranty obligation and
buyer's remedies hereunder are SOLELY
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 consumers for personal,
family, or household use, Symetrix ex-
pressly disclaims all implied warranties,
including but not limited to warranties of
merchantability and fitness for a particu-
lar 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 addi-
tional 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.
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.

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If you have determined that your 307 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], Monday through
Friday, 8AM (800 hours) though 4:30 PM (1630 hours) Pacific Time.
At the Symetrix factory, Symetrix will perform in-warranty or out-of-warranty service on any
product it has manufactured for a period of five years from date of manufacture.
In-warranty Repairs
To get your 307 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 shipping
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 307

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Wiring Diagram
Input
Channe
l
Input
Input
Channe
l
Channe
l
Channe
l
Input
Input
Output
Channe
l
Channe
l
Output
Channe
l
3 21
TIP
Pin 3 = Low
Pin 2 = High
Pin 1=Not Connected
Shield Tab = Not Connected
Balanced Terminal Strip
Balanced Female XLR
Sleeve = Not Connected
Ring = Low
Tip = High
RING
SLEEVE
TRS Plug
TS Plug
(When Using CHASSIS Ground)
(When Using CHASSIS Ground)
(When Using CHASSIS Ground)
(Wire Shield Not Connected)
(Wire Shield Not Connected)
TIP
132
TIP
SLEEVE
(Wire Shield Not Connected)
Sleeve = Low
Tip = High
(When Using CHASSIS Ground)
(Wire Shield Not Connected)
(When Using CHASSIS Ground)
Sleeve = Low
Tip = High
RCA Plug
(When Using CHASSIS Ground)
Shield Tab = Not Connected
Pin 1= Circuit Ground
Pin 3 = Low
Pin 2 = High
Balanced Male XLR
(When Using CIRCUIT Ground)
SLEEVE
Sleeve = Shield
Tip = High
TS Plug
Two Conductor
Shielded Cable
Two Conductor
Shielded Cable
Shielded Cable
Two Conductor
Two Conductor
Shielded Cable
Shielded Cable
Two Conductor
Shielded Cable
Shielded Cable
One Conductor
Shielded CableShielded Cable
Two Conductor
Appendix 1

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Declaration of ConformityChapter 9
Declaration of Conformity
We, Symetrix Incorporated,
14926 35th Ave. West, Lynnwood, Washington, USA,
declare under our sole responsibility that the product:
307 Dual Isolation Transformer
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 50081-1
Electromagnetic compatibility - Generic emission standard
Part 1: Residential, commercial, and light industry.
EN 50082-1
Electromagnetic compatibility - Generic immunity standard
Part 1: Residential, commercial, and light industry.
The technical construction file is maintained at:
Symetrix, Inc.
14926 35th Ave. West
Lynnwood, WA, 98037-2303
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: October 15, 1998
Place of issue: Lynnwood, Washington, USA
Authorized signature:
Dane Butcher, President, Symetrix Incorporated.

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Symetrix, Inc.
14926 35th Ave. West
Lynnwood, WA, 98037-2303
USA
Tel: [phone]
Fax: [phone]
Website: http://www.symetrixaudio.com
Email: [email protected]