Orban 275A User manual

Operating Manual
Automatic
Stereo Synthesizer
Model 275A

IMPORTANT NOTE: Refer to the unit’s rear panel for your Model Number.
Model Number: Description:
275A/U Stereo Synthesizer, 115V
275A/E Stereo Synthesizer, 230V
OPTIONS:
Model Number: Description:
275ARC Remote Control
275ASPK Spare Parts Kit
SCI Clear Security Cover
MANUAL:
Part Number: Description
95053-000-02 275A Manual
CAUTION: TO REDUCE the risk of electrical shock, do NOT REMOVE COVER (OR BACK).
NO USER SERVICEABLE PARTS INSIDE. REFER SERVICING TO QUALIFIED SERVICE PERSONNEL.
WARNING: TO REDUCE THE RISK OF FIRE OR ELECTRICAL SHOCK, DO NOT EXPOSE THIS
APPLIANCE TO RAIN OR MOISTURE.
This symbol, wherever it appears,
alerts you to the presence of uninsulated
dangerous voltage inside the enclosure —voltage
that may be sufficient to constitute arisk of shock.
This symbol, wherever it appears,
alerts you to important operating and
maintenance instructions in the accompanying
literature. Read the manual.

IMPORTANT SAFETY INSTRUCTIONS
All the safety and operating instructions should be read before the appliance is operated.
Retain Instructions: The safety and operation instructions should be retained for future reference.
Heed Warnings: All warnings on the appliance and in the operating instructions should be adhered to.
Follow Instructions: All operation and user instructions should be followed.
Water and Moisture: The appliance should not be used near water (e.g., near abathtub, washbowl, kitchen sink, laundry tub, in awet
basement, or near aswimming pool, etc.).
Ventilation: The appliance should be situated so that its location or position does not interfere with its proper ventilation. For example, the
appliance should not be situated on abed, sofa, rug, or similar surface that may block the ventilation openings; or, placed in abuilt-in
installation, such as abookcase or cabinet that may impede the flow of air through the ventilation openings.
Heat: The appliance should be situated away from heat sources such as radiators, heat registers, stoves, or other appliances (including
amplifiers) that produce heat.
Power Sources: The appliance should be connected to apower supply only of the type described in the operating instructions or as
marked on the appliance.
Grounding or Polarization: Precautions should be taken so that the grounding or polarization means of an appliance is not defeated.
Power-Cord Protection: Power-supply cords should be routed so that they are not likely to be walked on or pinched by items placed
upon or against them, paying particular attention to cords at plugs, convenience receptacles, and the point where they exit from the appliance.
Cleaning: The appliance should be cleaned only as recommended by the manufacturer.
Non-USe Periods: The power cord of the appliance should be unplugged from the outlet when left unused for along period of time.
Object and Liquid Entry: Care should be taken so that objects do not fall and liquids are not spilled into the enclosure through
openings.
Damage Requiring Service: The appliance should be serviced by qualified service personnel when:
The power supply cord or the plug has been damaged; or
Objects have fallen, or liquid has been spilled into the appliance; or
The appliance has been exposed to rain; or
The appliance does not appear to operate normally or exhibits amarked change in performance; or
The appliance has been dropped, or the enclosure damaged.
Servicing: The user should not attempt to service the appliance beyond that described in the operating instructions. All other servicing
should be referred to qualified service personnel.
The Appliance should be used only with acart or stand that is recommended by the manufacturer.
Safety Instructions (European)
Notice For U.K. Customers If Your Unit Is Equipped With APower Cord.
WARNING: THIS APPLIANCE MUST BE EARTHED.
The cores in the mains lead are coloured in accordance with the following code:
GREEN and YELLOW -Earth BLUE -Neutral BROWN -Live
As colours of the cores in the mains lead of this appliance may not correspond with the coloured markings identifying the terminals in your
plug, proceed as follows:
The core which is coloured green and yellow must be connected to the terminal in the plug marked with the letter E, or with the earth symbol,
(4-), or coloured green, or green and yellow.
The core which is coloured blue must be connected to the terminal marked Nor coloured black.
The core which is coloured brown must be connected to the terminal marked Lor coloured red.
The power cord is terminated in aCEE7/7 plug (Continental Europe). The green/yellow wire is connected directly to the unit's chassis. If
you need to change the plug and if you are qualified to do so, refer to the table below.
WARNING: If the ground is defeated, certain fault conditions in the unit or in the system to which it is connected can result in full line
voltage between chassis and earth ground. Severe injury or death can then result if the chassis and earth ground are touched simultaneously.
CONDUCTOR WIRE COLOR
Normal Alt
LLIVE BROWN BLACK
NNEUTRAL BLUE WHITE
EEARTH GND GREEN-YELLOW GREEN
AC Power Cord Color Coding

Safety Instructions (German)
Gerat nur an der am Leistungsschild vermerkten Spannung und Stromart betreiben.
Sicherungen nur durch solche, gleicher Stromstarke und gleichen Abschaltverhaltens ersetzen. Sicherungen nie uberbrucken.
Jedwede Beschadiguna des Netzkabels vermeiden. Netzkabel nicht knicken Oder quetschen. Beim Abziehen des Netzkabels den
Stacker und nicht das Kabel enfassen. Beschadigte Netzkabel sofort auswechseln.
Gerat und Netzkabel keinen ubertriebenen mechanischen Beaspruchungen aussetzen.
Um Beruhrung gefahrlicher elektrischer Spannungen zu vermeiden, dart das Gerat nicht geoffnet warden. Im Fall von Betriebsstorun-
gen dart das Gerat nur Von befugten Servicestellen instandgesetzt warden. Im Gerat befinden sich keine, durch den Benutzer
reparierbare Teile.
Zur Vermeidung von elektrischen Schiagen und Feuer ist das Gerat vor Nasse zu schiitzen. Eindringen von Feuchtigkeit und
Fliissigkeiten in das Gerat vermeiden.
Bei Betriebsstorungen bzw. nach Eindringen von Fliissigkeiten Oder anderen Gegenstanden, das Gerat sofort vom Netz trennen und
eine qualifizierte Servicestelle kontaktieren.
Safety Instructions (French)
On s'assurera toujours que la tension et la nature du courant utilise correspondent bien aceux indiques sur la plaque de I'appareil.
N'utiliser que des fusibles de meme intensity et du meme principe de mise hors circuit que les fusibles d’origine. Ne jamais shunter les
fusibles.
Eviter tout ce qui risque d’endommager le cable seceur. On ne devra ni le plier, ni I’aplatir. Lorsqu'on debranche Iappareil, tirer la fiche
et non le cable. Si un cable est endommage, le remplacer immediatement.
Ne jamais exposer I'appareil ou le cable aune contrainte mecanique excessive.
Pour eviter tout contact averc une tension electrique dangereuse, on noouvrira jamais I'appareil. En cas de dysfonctionnement,
I’appareil ne peut etre repare que dans un atelier autorise. Aucun element de cet appareil ne peut etre repare par Iutilisateur.
Pour eviter les risques de decharge electrique et d'incendie, proteger I'appareil de I'humidite. Eviter toute penetration d'humidite ou fr
liquide dans I'appareil.
En cas de dysfonctionnement ou si un liquide ou tout autre objet apenetre dans I'appareil couper aussitot I’appareil de son alimentation
et s'adresser aun point de service apresvente autorise.
Safety Instructions (Spanish)
Hacer funcionar el aparato solo con la tension yclase de corriente sehaladas en la placa indicadora de caracteristicas.
Reemplazar los fusibles solo por otros de la misma intensidad de corriente ysistema de desconexion. No poner nunca los fusibles en
puente.
Proteger el cable de alimentacion contra toda clase de danos. No doblar oapretar el cable. Al desenchufar, asir el enchufe yno el
cable. Sustituir inmediatamente cables danados.
No sometar el aparato yel cable de alimentacion aesfuerzo mecanico excesivo.
Para evitar el contacto con tensiones electricas peligrosas, el aparato no debe abrirse. En caso de producirse fallos de funcionamiento,
debe ser reparado solo por talleres de servicio autorizados. En el aparato no se encuentra ninguna pieza que pudiera ser reparada
por el usuario.
Para evitar descargas electricas eincendios, el aparato debe protegerse contra la humedad, impidiendo que penetren esta oliquidos
en el mismo.
En caso de producirse fallos de funcionamiento como consecuencia de la penetration de liquidos uotros objetos en el aparato, hay
que desconectarlo inmediatamente de la red yponerse en contacto con un taller de servicio autorizado.
Safety Instructions (Italian)
Far funzionare I'apparecchio solo con la tensione eil tipo di corrente indicati sulla targa riportante idati sulle prestazioni.
Sostituire idispositivi di protezione (valvole, fusibili ecc.) solo con dispositivi aventi lo stesso amperaggio elo stesso comportamento
di interruzione. Non cavallottare mai idispositivi di protezione.
Evitare qualsiasi danno al cavo di collegamento alia rete. Non piegare oschiacciare il cavo. Per staccare il cavo, tirare la presa emai
il cavo. Sostituire subito icavi danneggiati.
Non esporre I'apparecchio eil cavo ad esagerate sollecitazioni meccaniche.
Per evitare il contatto con le tensioni elettriche pericolose, I'apparecchio non deve venir aperto. In caso di anomalie di funzionamento
I’apparecchio deve venir riparato solo da centri di servizio autorizzati. Nell'apparecchio non si trovano parti che possano essere riparate
dalrutente.
Per evitare scosse elettriche oincendi, I'apparecchio va protetto dall’umidita. Evitare che umidita oliquidi entrino nell'apparecchio.
In caso di anomalie di funzionamento rispettivamente dopo la penetrazione di liquidi ooggetti nell'apparecchio, staccare immedi-
atamente I'apparecchio dalla rete econtattare un centra di servizio qualificato.

Operating Manual
Automatic
Stereo Synthesizer
Model 275A

This manual is part number 95053-000-02.
200 -FB -5/96
©Copyright 1996.
orbon
HAHarman International Company
1525 Alvarado Street, San Leandro, CA 94577 USA
Phone: [phone] •Fax: [phone] •E-mail: [email protected]

Table of Contents
SECTION 1: SYSTEM DESCRIPTION
AND APPLICATION
1-1 Performance Highlights
1-2 Fig. 1-1: Conceptual Block Diagram
1-3 Product Overview
SECTION 2: INSTALLATION
2-1 Overview of Installation Procedure
2-2 Fig. 2-1: Rear Panel
2-3 Remote Control Panel 273A/RC
2-3 Fig. 2-2: Chassis Configuration
for Remote Control
2-4 Power-up Jumpers
2-4 Fig. 2-3: Powerup Jumpers
2-5 AC Power
2-5 Fig. 2-4: AC Line Color Code
2-5 Mounting Rack Requirements
2-6 Audio Connections, Operating Level
2-7 Recognition Switch
2-7 Initial Program Tests
2-7 External Automation
2-8 Fig. 2-5: Control Interface Inputs
2-8 Fig. 2-6: Loopthrough Diagram
2-
9Registration Card
SECTION 3: OPERATING INSTRUCTIONS
Fig. 3-1: Front-panel Controls
3-
1Summary
3-2 General Operating Instructions
3-4 Further Discussion of Functions
SECTION 4: MAINTENANCE
4-1 Introduction
4-1 Preventive Maintenance
4-1 Corrective Maintenance
4-1 Service Access
4-2 Component Replacement
4-2 Replacement Parts
4-2 Replacement of PCB Components
4-4 Troubleshooting IC Opamps
4-4 Factory Service
4-
5Shipping Instructions
SECTION 5: ALIGNMENT AND
PERFORMANCE EVALUATION
5-
1General
5-1 Power Supply
5-1 Signal Processing Circuitry
5-2 Audio Path Alignment and Verification
5-4 Fig. 5-1: Noise Reduction Response
5-4 Fig. 5-2: Noise Reduction Response,
lOdB Below Expansion Threshold
5-4 Fig. 5-3: Frequency Response in
Synthesize Mode
5-4 Fig. 5-4: Synthesizer Response,
Narrow Mode
5-4 Fig. 5-5: Synthesizer Response,
Wide Mode
5-5 Control Circuit Bandpass Filter
Performance Verification
5-5 Fig. 5-6: Control Circuit
Bandpass Filter Response
5-5 Automatic Recognition Circuit Tests
5-6 275A/RC Interface Tests
5-7 User Control Interface Logic Tests

SECTION 6s CIRCUIT DESCRIPTION APPENDIX A: GUIDE FOR THE MASTER
CONTROL OPERATOR
6-1 Main Audio Path
6-1 Input Buffer
6-1 Crossfade Circuit APPENDIX Bs INTERNAL TRIMS
6-2 Noise Reduction Circuit
6-3 Fig. 6-1: IC12 Pinout, Diagram
6-3 Stereo Synthesizer APPENDIX C: INSTALLATION OF REMOTE
6-3 Auto Polarity Circuit CONTROL PANEL 275A/RC
6-4 L+R Peak Detector
6-4 L+R/L-R Comparator, Time Constant C-l Introduction
6-5 Mono/Stereo Recognition Circuit C-l Connector
6-5 Single Channel Recognition C-l Fig. C-l: Connector Wiring Diagram
6-6 Center Channel Recognition C-2 Cable
6-7 Control Logic C-2 Table C-l: Potentially Useful Cables
6-7 General C-2 Additional Remote Control Panels
6-7 Comb Bandwidth C-3 Temporary Removal of 275A/RC Panel
6-7 Noise Reduction OPERATE/DEFEAT
6-8 Auto Polarity ON/OFF
6-8 Basic Mode Switching, General APPENDIX D: CONSTRUCTING APHASE-
6-8 Input Decode and Latches DIFFERENCE NETWORK
6-9 Pulse/Continuous Logic
6-9 User Interface Status Sensor D-l Theory
6-10 Crossfade Ramp Generator D-2 Fig. D-l: Phase Differences
6-10 Latch and Left/Right Decode Logic D-2 Fig. D-2: Mono Sum Errors
6-11 Active Status Lamps D-2 Implementation
6-11 Automation Lockout Circuit D-3 Application and Operation
6-11 Remote Control D-4 Fig. D-3: Network Schematic
6-12 Power Supply
6-12 LED Brightness
APPENDIX E: PARTS LIST
APPENDIX F: SPECIFICATIONS
APPENDIX G: SCHEMATICS AND PARTS
LOCATOR DRAWINGS

Front Panel
Hear Panel
ORBAN MODEL 275A AUTOMATIC STEREO SYNTHESIZER

SECTION 1:
System Description And Application
1.PERFORMANCE —Stereo inputs and outputs
HIGHLIGHTS Designed to be placed permanently in series with the program line.
—Fully compatible with mono receivers
They reproduce the synthesizer's original mono input.
—Audio-controlled switching between true and synthesized stereo
Synthesizer is activated when audio is absent on one channel and, optionally,
when both channels are nearly equal. In addition, local and remote manual
override control is available.
—Smooth "cross-fade" switching between modes
Program-adaptive crossfade rate avoids clicks and pops.
—Automatically detects and corrects polarity-reversals
Automatically corrects "out-of-phase" stereo inputs.
—Phase-shift-derived comb filter stereo synthesis
Orban's patented phase-shift-derived comb filter stereo synthesis technique. Two
remote-selectable stereo synthesis modes allow matching the spatial perspective
to the program material. "Narrow" mode centers dialogue. "Wide" is more
dramatic on music and effects.
—Single-ended dynamic noise reduction
Acombination of program-controlled lowpass filtering and downward expansion
is available for noise reduction on synthesized material. lOdB reduction of hiss
and hum is typically achieved.
—Optically-isolated automation control of all functions
—Optional 19" rack-mount Remote Control Panel
Duplicates main unit control panel.
—Fully-balanced, transformerless inputs and outputs
+26dBm clipping level permits use with +4 or +8dBm lines.
—Space-saving chassis
Mounts in 13/4" of rack space.
1-1

Fig. 1-1: Conceptual Block Diagram, Model 275A Automatic Stereo Synthesizer

2. PRODUCT
OVERVIEW
The Orban 275A performs this function and also includes other useful features and
functions.
The four primary functions are:
1) Mono/Stereo Detection and/or Single-Channel Recognition
2) Stereo Synthesis of Mono Material
3) Automatic Reverse-Polarity Detection And Correction (for true stereo material)
4) Dynamic Noise Reduction (in Synthesize mode only)
Because of the continuing use of program material with mono soundtracks in the age
of stereo TV, most TV stereo broadcasters need an automatic device that monitors the
program audio and that effectively reprocesses mono material into pseudo-stereo,
augmenting the entertainment value of mono material without operator intervention.
Fig. 1-1 shows aconceptual block diagram which may be helpful in understanding the
unit. Amore complete explanation of the functions is found in Section 3(Operating
Instructions).
1) Mono/Stereo Detection
Mono source material is automatically distinguished from stereo by two techniques:
if a) audio is absent from one channel, or b) both channels have nearly identical
material, the source is considered mono and the stereo synthesizer is activated.
Otherwise, the source is considered stereo and the signal bypasses most of the rest
of the system.
Some slack is provided in the recognition circuitry to compensate for the
interchannel phase shifts and level imbalances inevitable in real-world operations.
The amount of slack is internally adjustable by the user.
The recognition technique based on nearly identical channels can be defeated by a
rear-panel switch. Then, operation of the stereo synthesizer can be controlled
unambiguously in production by muting one channel when stereo synthesis is desired
and by providing both channels when Bypass mode is desired, thus improving the
reliability of automatic detection.
NOTE:
While the transition between true stereo and synthesized stereo is graceful,
certain types of "stereo" program material may cause overly frequent
transitions. An example is atalk show where center-channel (i.e., mono)
dialogue is frequently alternated with music or crowd noises. In such cases,
it may be desirable to make the unit treat aU material as stereo by forcing
the unit into Bypass mode manually (or with overriding automation).
Error-free recognition of most stereo programs is technically impossible
because equal material in both channels will always be recognized as mono
(by definition). The Orban 275A is superior because it makes fewer errors
than other units.
1-3

In addition, special signal and control nodes have been brought out on a
rear-panel connector to readily interface future circuitry that might be
developed to further reduce the incidence of errors.
Appendix Dprovides instructions for building acircuit that introduces a
differential phase shift of 20° to 30° between the left and right channels
over afrequency range of lOO-lOOOHz. This phase shift has negligible
effect upon the stereo imaging and mono sum, but will unambiguously force
all stereo program material passed through it to be recognized as stereo.
True stereo material can thus be encoded through this circuit prior to
broadcast to assure that the recognition circuit cannot switch to Synthesize
mode. It is hoped that the networks will use asimilar means to
automatically encode true stereo material to avoid recognition errors.
2) Stereo Synthesis
The Stereo Synthesizer operates on mono material only. It creates apseudo-stereo
effect from the mono by dividing the audio spectrum into several frequency bands
and by directing these bands alternately to the left and right channels. The ear
perceives this as a stereo-like effect with substantial depth and arelatively wide
spatial perspective, but with little specific directionality. The mono listener
receives the stereo sum signal, which is identical to the mono input (or the mono
input as processed by the Noise Reduction circuit, if activated), and which is free
from phase cancellations and other errors.
When the synthesizer is automatically activated by recognition of nearly identical
channels, stereo is synthesized from the left channel. If the synthesizer is
automatically activated by recognition of "one-channel-only", it will synthesize
from the active input channel. Either left or right channel inputs can be selected
for synthesis —manually, or remotely by external automation.
(Due to the potential for small phase discrepancies between the left and right
channels in most plants, we do not provide amethod of synthesizing from the sum
of the channels, which is likely to be slightly degraded by phase cancellations.)
The stereo synthesizer has two modes: Wide and Narrow. The Wide mode creates a
few wide frequency bands and results in adramatic sense of stereo space on music
and effects. The Narrow mode creates many narrow frequency bands and is better
suited for programs heavy in dialogue where it is important that voices appear
from the center of the stereo space. In Narrow mode, the stereo impression on
music is less vivid. ASEPARATION control allows adjustment of the relative width
of the stereo soundstage.
The Wide or Narrow mode is selected manually or by an external automation
system.
3) Automatic Polarity Detector/Corrector
This circuit operates on stereo material (in Bypass mode) only. The channels are
monitored for apolarity reversal (which could seriously affect the quality of the
mono sum). When apolarity reversal is detected, it is automatically corrected.
Such polarity reversals can occur due to errors in production, transmission, or
patching.
1-4

This feature may be turned on and off manually or by automation. It may be
D
desirable to turn it off when broadcasting Dolby stereo soundtracks, since out-of-
phase "surround" information has been purposely mixed into many such tracks to
activate the rear-channel "surround" speakers in atheater. Such material, if it
dominates the mix, may falsely trigger the Automatic Polarity Corrector.
4) Noise Reduction
Noise reduction operates on synthesized mono material only. Stereo material is not
generally contaminated by excess noise and would not greatly benefit from this
type of noise reduction. This single-ended dynamic noise reduction system can be
used with any mono program material to achieve lower noise while minimizing
perceived high frequency loss due to the noise reduction function. It is particularly
useful for films with optical sound.
The noise reduction function combines program-controlled lowpass filtering (to
reduce hiss) with wideband downward expansion (to reduce low-level hum, rumble,
sprocket noise, and other such noise).
The noise reduction is activated or defeated manually or by external automation.
5) Other Features
All functions can be selected at the front panel or at the optional Orban Remote
Control Panel 275A/RC, which may be located up to about 5000 feet away from
the main 275A chassis (see Appendix C). The 275A can be also controlled by an
external automation system. (In case of automation problems, the manual controls
can override those automation signals which select stereo synthesis modes.)
The automation signals controlling stereo synthesis may be either continuous
voltages or pulses, depending on the setting of the rear-panel PULSE/CONTINUOUS
switch. In PULSE mode, the automation duplicates the function of the buttons: A
pulse will latch the logic. In CONTINUOUS mode, acontinuous automation voltage
will immediately override the manual controls; the logic will revert to its former
state ("standby" state) when the voltage is removed.
The standby state may even be changed by means of the buttons while an
overriding voltage is present; the synthesizer will not change state until the
continuous voltage is removed. The standby state will usually be AUTO (i.e.,
control by the 275A's internal recognition circuit), although any other state may be
chosen if appropriate.
These various alternatives provide considerable flexibility in integrating the 275A
with various automation schemes.
Stereo inputs and outputs are active-balanced. Inputs are bridging and can be
selected for +4dBm or +8dBrn nominal levels by means of arear-panel switch.
Outputs can provide +26dBm into 600 ohms. Normally, 150:600-ohm transformers
must be used in 150-ohm systems.
1-5

SECTION 2:
Installation
1. OVERVIEW OF
INSTALLATION
PROCEDURE
1. Read Section 1(System Description and Application).
2. Install optional remote control and set internal plug, if desired.
3. Reposition internal powerup jumpers, if desired.
4. Check AC power strapping; restrap, if desired.
5. Mount unit in rack.
6. Connect audio inputs and outputs; set rear-panel OPERATING LEVEL switch.
7. Set rear-panel center-channel RECOGNITION switch.
8. Perform initial program tests.
9. Connect automation through User Control Interface, if desired.
10.
Return Registration Card to Orban.
IMPORTANT
READ THE INSTRUCTIONS IN THIS SECTION. This unit may not
function properly unless these instructions are followed carefully.
DO NOT MOUNT THE UNIT DIRECTLY ABOVE LARGE, HEAT-
PRODUCING DEVICES, such as vacuum-tube power amplifiers, as this
may shorten component life. Ambient temperature should not exceed
113°F (45°C) with equipment on.
If you are installing the optional Orban Remote Control Panel 275A/RC,
and/or if you are going to use the synthesizer audio loop-through connection
(on the User Control Interface connector) to add external processing to the
synthesized signal, DO NOT MOUNT THE MAIN CHASSIS in the rack
until you have read Sections 2.2 (Remote Control) and 2.9 (External
Automation).
WARNING
DO NOT DEFEAT AC POWER GROUND. If the ground is defeated,
certain fault conditions in the unit or in the system to which it is
connected can result in full line voltage between chassis and earth ground.
Such voltage can cause electrical shock resulting in severe injury or death.
2-1

OPERATING LEVEL set-up switch:
Selects +4dBm or +8dBm nominal operating
level (labels valid for 600-ohm systems only).
Affects only the Noise Reduction circuit,
changing its threshold as appropriate.
RECOGNITION set-up switch:
Determines the recognition method of the
AUTO recognition circuit: one-channel-absent
is always recognized; when the switch is set
to M/S+1CH, nearly identical material on
both channels is also recognized.
Orban REMOTE CONTROL PANEL 275A/RC
connector:
(Mates with DC-37M connector, supplied with
275A/RC.) Carries lines for the duplication
of all controls and indicators appearing on the
front panel, except for the SEPARATION
control. To use this connector, an internal
plug must be moved (see following page). If
this plug is in the wrong position, no front-
panel lamps will light and the unit will not
operate normally.
Automation Mode set-up switch:
The PULSE setting causes the logic to latch
on incoming automation pulses (through the
25-pin USER CONTROL INTERFACE
connector). The CONTINUOUS setting causes
the logic state to follow continuous voltages
and to revert to the standby default state
when no voltage is present. (See Other
Features in Section 1.)
USER CONTROL INTERFACE connector:
(Mates with DB-25M connector, not supplied.)
Offers optically-isolated inputs to interface
with external automation. Allows control of
ali front-panel functions except SEPARATION
control. Also includes audio and control nodes
to interface with auxiliary equipment that
may be developed in the future. (See
Appendix Cfor wiring instructions.)
Fig. 2-1: Rear-panel Connectors and Switches
2-2

2. REMOTE CONTROL
PANEL 275A/RC
(Optional)
[See Appendix Cfor wiring instructions.]
The Remote Control Panel replicates the main chassis' front panel, except that the
SEPARATION control is omitted. The Panel is powered from the main chassis, and is
connected to it by means of a19-pair cable terminated at both ends with a37-pin
DC-37 connector. Both connectors are supplied. The customer must provide the cable.
Strictly speaking, shielding of the cable is unnecessary (although it may be wise in a
high-RF environment). The only requirement is that the total end-to-end resistance of
any wire within the cable be less than 100 ohms. Check before you buy to make sure
that the cable is compatible with your plant wiring practices and local building codes.
Some cable suggestions are shown in Appendix C.
To configure the main chassis: Remove the top cover of the main chassis. The unit
is shipped from the factory with one ribbon cable from the front panel plugged into a
16-pin DIP socket, J5, located towards the rear panel. This is correct for non-remote
operation. For remote operation, this cable must be unplugged from J5 and plugged
into J4, which is immediately to the right of J5 when observed with the front panel
facing you (see Fig. 2-2).
IMPORTANT!
Since all lamps are wired in series (including those which activate the
275A's optically-coupled crossfade function), the 275A will not work
(although it will not be damaged) if the cable is plugged into J4 when the
273A/RC Remote Control Panel is not correctly connected. In particular,
no lamps will light. If the Remote Control Panel is to be disconnected for
any reason, the 275A's internal cable must either be repositioned to J5,
or an appropriate external user-supplied jumper plug must be
inserted in the Remote Control Panel connector to achieve normal
operation. See Appendix Cfor awiring diagram.
Fig. 2-2: Chassis Configuration For Remote Control Operation
2-3

3. POWER-UP
JUMPERS As shipped, the 275A will power up as indicated in following table. To select an
alternative power-up configuration, reposition the appropriate jumpers according to
Fig. 2-3.
As Shipped Alternatives
SYNTH FROM L
Jumper
Mode AUTO SYNTH FROM R
BYPASS B
Auto
Polarity ON OFF C
Comb
Bandwidth NARROW WIDE E
Noise
Reduction OPERATE DEFEAT D
Fig. 2-3: Powerup Jumpers
2-a

4. AC POWER
5. MOUNTING RACK
REQUIREMENTS
The power transformer can be connected for 115-volt or 230-volt, 50 or 6QHz AC
operation. If a230-volt option was specified when the unit was ordered, atag on the
power cord warns of the modification.
The two primary windings of the power transformer are connected in parallel for 115-
volt operation and in series for 230-volt operation. (See the Schematic Diagram in
Appendix E.)
To strap the power transformer for adifferent voltage, remove the top cover.
Strapping instructions are found on the insulating fishpaper around the power
transformer. It is not necessary to rearrange the heavy insulated wiring; all strapping
can be performed with bare jumper wire. Take care not to burn the insulation.
The power cord is ordinarily terminated in a"U-Ground" plug to USA standards. The
green/yellow wire (which is connected to the long prong) is connected directly to the
275A chassis. Circuit ground is connected to the chassis ground by means of asingle
green wire adjacent to the power transformer. If it becomes necessary to isolate the
audio ground from the chassis to eliminate hum due to ground loops, this wire may be
disconnected.
WARNING!
If the chassis ground itself is defeated, certain ground fault conditions in
the unit or in the system to which it is connected can result in appearance
of full line voltage between chassis and earth ground. Such voltage is
capable of causing electrical shock, possibly resulting in severe injury or
death.
CONDUCTOR WIRE COLOR
Normal Alt
LLINE BROWN BLACK
NNEUTRAL BLUE WHITE
EEARTH GND GREEN-YELLOW GREEN
Fig. 2-4:AC Line Cord Color Coding
Vertical space of one standard rack unit (1 3/4"/4.5cm) is required for the 275A or the
275A/RC Remote Control Panel.
It is expected that either the main chassis or the optional Remote Control Panel would
be located at Master Control.
2-5

6. AUDIO
CONNECTIONS
AND OPERATING
LEVEL
Inputs and outputs are presented on aCinch 140-Ybarrier strip (//5 screw), which will
accommodate either spade lugs or afanning strip (for quick connect/disconnect).
1) Input:
The inputs are active single-amplifier quasi-balanced bridging, and will clip if levels
in excess of +26dB (ref .775V) are applied to them. (High common-mode rejection
will be maintained if the impedance driving the inputs is 600 ohms or less.)
Arear-panel switch sets the threshold of the Noise Reduction circuit for various
operating levels. Set the switch as follows:
Source Level Switch
+4dBm/600ohms +4
+8dBm/600ohms +8
+8dBm/150ohms (no transformer) +4
+8dBm/150ohms (150:600-ohm transformer) +8
2) Output:
The outputs are active balanced-to-ground with abalanced source impedance of 94
ohms. DO NOT GROUND EITHER SIDE OF AN OUTPUT, as this will short one
output amplifier to ground through a47-ohm resistor (although the output
amplifiers are protected against short circuits, shorts to ground will thermally
stress them, and will also introduce highly distorted currents into the audio ground
system which might crosstalk into other signal paths). If you want to drive an
unbalanced load, connect it between a(+) output and ground.
The outputs will interface correctly with +4 and +BdBm 600-ohm systems. However,
they will tend to clip if an attempt is made to drive a+8dBm 150-ohm system. In
such asystem, it is necessary to reduce input levels such that the peak current
delivered to the line is 30mA.
[To maintain 16dB headroom, it is necessary to limit the nominal "0" level of a
150-ohm system to +2.3dBm (-3.73dBu; 504mV rms) or less if the output of the
275A is connected directly to the line. Unity gain and satisfactory headroom
performance can only be achieved in a+8dBm 150-ohm system if 150:600-ohm
transformers are placed at the 275A's input and output.]
As shipped, the 275A is calibrated for unity gain into a600-ohm load in Bypass
mode. (The gain in Synthesize mode is frequency-dependent.)
It is important to maintain consistent polarity at left and right inputs, and at the
left and right outputs. If the inputs are wired in reverse polarity ("out-of-phase"),
this will be indicated by virtually constant illumination of the 275A's polarity
INVERTED lamp (provided that the AUTO POLARITY function is ON). No
indication will be provided if the outputs are wired in reverse polarity, but virtually
no sound will be heard from mono receivers when mono program material is
broadcast and the 275A is in Bypass mode.
2-6