Orban OPTIMOD-FM 8100A/1 User manual

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Operating Manual
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Operating Manual
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orban
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95039-000-04 5/86
Orban Associates Inc., 645 Bryant St., San Francisco, CA 94107 USA
Toll Free [phone]; In California, [phone] Telex: 17-1480
U.S Patents #4,460.871; #4,249.042; #4,208.548 U.K. Patent #2,001,495
Other Patents Pending. "OPTIMOD-FM" Is a Registered Trademark of Orban Associates Inc.
© 1980 by Orban Associates Inc.

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Issue 2 (revised July 1986)
FIRST DITION
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1
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CAUTION
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(per UL 813)
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Cards #5, #6, and #8/9 have been reconfigured in the Model 8100A/1 to allow use of
the optional Model 8100A/XT Six-Band Limiter Accessory Chassis. The motherboard
has been changed, and a prewired Accessory Port has been included to interface the
Accessory Chassis.
OPTIMOD-FM is a registered trademark of Orban Associates, Inc.
Smart Clipper is a trademark of Orban Associates, Inc.
Dolby is a registered trademark of Dolby Laboratories, Inc.
8100A/XT Six-Band Limiter Accessory Chassis
which is used to obtain improved source-to-source consistency and/or
presence on smaller radios and in cars.
The Model 8100A/1 processor differs from the Model 8100A in that it has been
modified for use with other Orban products such as:
The installation and servicing instructions in this manual are for use by
qualified personnel only. To avoid electric shock do not perform any
servicing other than that contained in the Operating Instructions unless you
are qualified to do so. Refer all servicing to qualified service personnel.
New information on the optional FM Filter Card (#0) has been added. Appendix K
(Audio Quality Considerations in FM Plants) has been updated, as have references
to FCC regulations.
In the current revision of this manual, references to the Dolby^ 334 Noise Reduction
Processor (including the interface information formerly contained in Appendix G) have
been deleted. Please contact Customer Service for Dolby 334 interface information.
References to FM quadraphonic broadcasting have also been deleted.
A new Appendix G gives information on changing the unit's preemphasis for those
countries with a preemphasis standard different from the one used in the USA.
This manual is for use with all OPTIMOD-FM^ Models 8100A/1 to date. It is not
directly applicable to the 8100A/l ’ s immediate ancestor, the Model 8100A.

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Table of Contents
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INTRODUCTION AND SYST M D SCRIPTION
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APPLICATION
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INSTALLATION
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INITIAL S TUP PROC DUR
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OP RATING INSTRUCTIONS
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SYST M P RFORMANC V RIFICATION
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ROUTIN MAINT NANC
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SYST M D SCRIPTION
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CIRCUIT D SCRIPTION
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US R ACC SS
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FI LD AUDIT-OF-P RFORMANC PROC DUR
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FI LD ALIGNM NT PROC DUR AND SP CIFICATION
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Q
APPENDICES
TROUBL DIAGNOSIS AND CORR CTION
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CHANGING PR MPHASIS
D TAIL D XCIT R INT RFAC INSTRUCTIONS
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SCH MATICS, PARTS LOCATORS, AND PARTS LISTS
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AUDIO QUALITY CONSID RATIONS IN FM PLANTS
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SP CIFICATIONS
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FUNCTIONS OF JUMP RS ON PC CARDS
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Table of Contents
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PR FAC
1
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INTRODUCTION AND SYST M D SCRIPTION
1:
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4; INITIAL S TUP PROC DUR
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Separation Scope Pattern
APPLICATION
2:
5: OP RATING INSTRUCTIONS
INSTALLATION
3:
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Pilot Phase Scope Pattern
Pilot Phase Scope Pattern, xlO
4-1
4-2
4-3
4-3
4-4
4-4
4-4
4-5
4-5
General
Functions Of The Setup Controls
Input Attenuators
Release Time
Clipping
High Frequency Limiting
Bass Coupling
Gate Threshold
Start At The Bass Coupling Control
Adjusting The Other Controls
Clipping
Release Time And Amount Of Gain Reduction
High Frequency Limiting
Gate Threshold
Why Certain Controls Aren't There
Summary
Powerup Mode
Fig. 3-2: Powerup & Mono Mode Jumpers
Mono Mode
Input Attenuator Pads
Fig. 3-3: Input Attenuation Jumpers
Defeating The 30Hz Highpass Filters
Reassembly
Initial lectrical Checkout
quipment Location
Mounting And Grounding
Input Signal Connections
Studio Chassis Output Connections
Composite Output Connection
Balanced xciter Input
Unbalanced xciter Input
Remote Control
Remote Gain Reduction Meter
2-1
2-2
2-3
2-3
2-3
2-3
2-3
2-4
2-4
Function Of OPTIMOD-FM
Fig. 1-1: Signal Flow Diagram
Simplified System Description
Input Conditioning Filter
Dual-Band Compressor
Preemphasis and High Frequency Limiter
FM Smart Clipper
Frequency-Contoured Sidechain Overshoot Corrector
Stereo Generator
VU Meter
Studio Accessory Chassis
Six-Band Limiter Accessory Chassis
FM Filter Card
5-1
5-2
5-2
5-2
5-2
5-2
5-2
5-2
5-3
5-3
5-3
5-4
5-5
5-5
5-6
5-7
3-3
3-3
3-3
3-4
3-3
3-4
3-4
3-5
3-5
3-6
3-6
3-6
3-6
3-6
3-7
3-7
3-8
3-1
3-1
3-2
3-2
3-3
Registration Card
Packing Material
User Feedback Form
FCC Filing (USA)
Security (Keys and Locks)
1-2
1-3
1-4
1-4
1-4
1-5
1-6
1-8
Studio-Transmitter Links
xciters
RCA BT -15 xciter
Gates T 1, T 3 xciters
Collins 310Z/Continental 510R-1 xciters
RF Amplifiers and Antennas
SCA
Remote Control Functions
Difficult nvironments
Registration Card
Unpacking and Initial Inspection
Physical xamination
Power Considerations
Fig. 3-1: Power Cord Compatibility
Initialization Options
Dual-Chassis Alignment
Stereo Generator
Separation
Fig. 4-2:
Pilot Phase
Fig. 4-3:
Fig. 4-4:
Program Tests
Fig. 4-5: Setup Controls

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5-9
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SYST M P RFORMANC V RIFICATION
6:
CIRCUIT D SCRIPTION
APP NDIX B:
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ROUTIN MAINT NANC
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APPENDICES
SYST M D SCRIPTION
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6-1
6-1
6-1
6-2
6-2
6-3
6-3
6-3
6-3
6-4
6-4
General
Input Amplifier
30Hz Highpass Filter
Allpass Phase Scrambler And Preemphasis/Deemphasis
Dual-Band "Master/Bass" Compressor
Crossover And Bass Clipper
Voltage-Controlled Amplifier Operation
Compressor Control Circuitry
Mono Performance Verification
Stereo Performance Verification
Main Channel
Subchannel
Separation
Crosstalk
38kHz Subcarrier Suppression
Pilot Frequency
Fig. 6-1: Pilot Frequency Test Point
Pilot Injection
Rear-Panel T ST Jacks
General
Routine Performance Verification
Stereo Generator Tests
Dynamic Separation
38kHz Suppression
Pilot Injection
Audio Processing
A-5
A-5
A-6
A-7
A-7
A-7
A-8
A -9
A-10
A-10
A-10
A-10
A-10
A-ll
A-12
B-l
B-l
B-l
B-2
B-2
B-2
B-2
B-3
B-5
B-6
B-6
B-7
B-7
B-8
B-8
B-9
B-10
B-ll
B-12
B-12
B-13
B-13
B-14
B-15
B-16
B-17
B-17
Phase-Corrected Lowpass Filter/Preemphasis
High Frequency Limiter
FM Smart Clipper
Clipper With Dynamic Threshold
15kHz Phase-Corrected Lowpass Filter
Distortion-Cancelling Sidechain
Frequency-Contoured Sidechain Overshoot Compensator
Stereo Generator:
19kHz Oscillator
19kHz- Doubler
38kHz Filter And Phase Shifter
38kHz AGC Loop
38kHz Phase-Locked Loop
Stereo Modulator
Mode Switching Logic
A-12 Power Supplies
5-8
5-8
5-8
5-8
5-8
5-8
5-9
5-9
' 5-9
5-9
General
Input Amplifier
30Hz Highpass Filter
Allpass Phase Scrambler And Preemphasis/Deemphasis
Dual-Band "Master/Bass" Compressor
Crossover And Bass Clipper
Voltage-Controlled Amplifier Operation
Compressor Control Circuitry
Gain Reduction Metering
Gating Circuitry
Phase-Corrected Lowpass Filter/Preemphasis
Differential Preemphasis And High Frequency Limiter
High Frequency Limiter Control Circuitry
FM Smart Clipper
Clipper With Dynamic Threshold
15kHz Phase-Corrected Lowpass Filter
2.2kHz Distortion-Cancelling Sidechain
B-10 Frequency-Contoured Sidechain Overshoot Compensator
B-ll Stereo Generator:
19kHz Oscillator
19kHz Doubler
38kHz Filter And Phase Shifter
38kHz AGC Loop
38kHz Phase-Locked Loop
L-R Amplifier
38kHz Doubly-Balanced Modulator
L+R/Mono Path
Output Summing Amplifier
Mode Switching Logic
B-17 Unregulated Power Supply
B-18 +15 Volt Regulator
B-19 -15 Volt Regulator
B-19 Miscellaneous Voltage Supplies
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7-2
7-2
7-2
G TTING TH SOUND YOU WANT
To Obtain More Loudness
To Obtain More Brightness
To Obtain More Bass
To Obtain Less Bass
To Make "Air" Sound Most Like "Program"
To Obtain "Open" Sound
To Obtain A "Heavily-Processed" Sound
To Avoid "Noise Pump-Up"
To Achieve More Subtle Gain Riding
On Wide-Dynamic Range Material
To Avoid Excessive Sibilance
| APP NDIX A:
A-l
■ A-l
B a - i
A-2
— A-2
|A-3
" a -3
A-4
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APP NDIX F:
APP NDIX C:
US R ACC SS
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APP NDIX D:
FI LD AUDIT-OF-P RFORMANC
CHANGING PR MPHASIS
APP NDIX G:
APP NDIX H:
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APP NDIX J:
APP NDIX :
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1
C-l
C-l
C-l
C-l
C-l
C-l
C-2
C-2
C-3
C-3
C-3
D-l
D-l
D-2
D-2
D-2
D-2
D-3
D-4
D-5
D-5
D-6
D-6
D-6
D-7
D-7
D-8
Routine Access
User Adjustments
Line Fuse, Power Switch, and Line Voltage Selector
Circuit Cards
Service Access
General Cautions
Cover Removal
Access To Area Behind Rear Panel
Access To RF Filter Card
Access To Unregulated Power Supply Chamber
Removal Of Card Z/l (The DC Regulator) From
Rear Panel And Power Transistor Replacement
FI LD ALIGNM NT PROC DUR
AND SP CIFICATION
Pilot Phase Scope Pattern
Pilot Phase Scope Pattern, xlO
F-13
F-13
H-l
H-l
H-2
H-2
J-3
J-5
J-7
J-9
J-ll
J-13
J-15
J-17
J-23
J-34
J-l
J-l
TROUBL DIAGNOSIS
AND CORR CTION
D TAIL D XCIT R INT RFAC
INSTRUCTIONS
SCH MATICS,
PARTS LOCATORS,
AND PARTS LISTS
-4
-4
-5
-6
-7
-8
-8
-l
-l
-2
-2
F-l
F-2
F-2
F-2
F-2
F-3
F-4
F-4
F-4
F-5
F-9
F-10
F-10
F-ll
Collins 310Z-KB)
Continental 510R-1 (Collins 310Z-2)
Gates (Harris) T -1 And T -3
RCA BT -15
General
Required quipment
Audio Processing
Standard Control Setup
Skeleton Proof
Fig. D-l: 75us Deemphasis Network Schematic
Fig. D-2: Standard 75us Preemphasis Graph
Operate-Mode Measurements
Stereo Generator
Stereo Performance Measurements
Crosstalk
38kHz Suppression
Separation
Pilot Phase
Remote Control And Logic Verification
Optional Measurements Using Spectrum Analyzer
General
Table Of Contents For Appendix J
Schematics With Parts Locators
Card //PS
Card Z/3/Z/4
Card Z/5
Card Z/6
Card Z/7
Card//8///9
Input Filter
Meter Resistor
J-18 Accessory Port Wiring
J-21 BLOCK DIAGRAM
J-23 Parts List
Obtaining Spare Parts
Vendor Codes
General
Problem Localization Routine
General Principles
Power Supply Tests
VU Meter Techniques
Card Swap Technique
Fig. F-l: Card Z/6 Channel Reversal Jumpers
Cards Common To Both Channels
Failures Not Diagnosed By Card-Swapping
CATALOG OF SYMPTOMS AND POSSIBL CAUS S
Factory Assistance
F-10 Troubleshooting At The Component Level
Troubleshooting IC Opamps
Ordering Replacement Parts
Replacing Printed Circuit Board Components
F-13 Shipping Instructions
Circuit Cards
Shipping The Complete Chassis
General
Required Test quipment And Materials
Card Z/l (Power Supply)
Cards Z/3/Z/4 (Input Buffer/Input Conditioning Filter/
Compressor Audio Path)
Card Z/5 (Compressor Control/Gating Detector)
Card Z/6 (Preemphasis/HF Limiter)
Fig. -l: Deemphasized System Frequency Response
Cards Z/8/Z/9 (FM Smart Clipper/FCS Overshoot Corrector)
Fig. -2: Distortion Cancellation Swept Response
Fig. -3: Overshoot Compensator Overdriven by 5kHz
Card Z/7 (Stereo Generator)
-ll Fig. -4: Separation Scope Pattern
-ll Fig. -5:
-ll Fig. -6;

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APP NDIX K:
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SP CIFICATIONS
APP NDIX L:
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APP NDIX M:
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K-l
K-l
K-4
K-4
K-4
K-4
K-5
K-5
K-6
K-6
K-9
K-9
K-10
K-ll
K-ll
K-13
K-13
K-14
K-14
K-15
K-15
AUDIO QUALITY CONSID RATIONS
IN FM PLANTS
FUNCTIONS OF JUMP RS
ON PC CARDS
General
Disk Reproduction
Tape
Sum-And-Difference Recording
Audio Time Base Correctors
Cheap Tape
Tape Speed
Use Of Noise Reduction
Tape Recorder Maintenance
Tape Recorder Alignment
Cartridge Machine Maintenance
Compact Disc
K-10 System Considerations
Headroom
Voice/Music Balance
lectronic Quality
K-13 Production Practices
General
Choosing The Monitor Loudspeakers
Loudspeaker Location
Loudspeaker qualization
Other Production quipment
Production Techniques and Practices
K-18 Summary

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Preface
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If the Registration Card has become lost or you have purchased the unit used, please
photocopy the image of the card reproduced on the following page and send it to us in
an envelope. Use the address shown on the title page.
Registration is of benefit to you because it enables us to tell you of new applications,
possible performance improvements, service aids, etc., which may be developed over
the life of the product. It also provides us with the date of sale so that we may more
promptly respond to possible claims under Warranty in the future (without having to
request a copy of your Bill of Sale or other proof of purchase).
Do not allow your Dealer to submit the card for you. If he forgets, you can miss
important future mailings and may be delayed in obtaining Warranty service.
Registration Card: The original purchaser should have received a postpaid
Registration Card packed with this manual.
The second section contains Appendices which provide useful information that you may
need at some time during the life of OPTIMOD-FM. This is primarily reference
material, and you do not need to digest it to install, set up, or operate your unit.
This Manual is organized into two major sections. The first contains information on
how to plan your installation, how OPTIMOD-FM^ interfaces with other station
equipment, how to set up and adjust OPTIMOD-FM, how to do an in-system
performance verification, and brief comments on routine maintenance. You should read
Parts 1, 2, and 3 before attempting to install OPTIMOD-FM.
There is no Index, so the TABL OF CONT NTS should be used to help you find the
information you want. The TABL OF CONT NTS provides an overview of the
organization of the manual, and lists in some detail the topics discussed.
Packing Material: The carton in which your OPTIMOD-FM was shipped was carefully
designed to prevent damage from the stresses ordinarily encountered in commercial
shipments. SAV TH CARTON AND ALL PACKING MAT RIAL in case you ever
have to ship the OPTIMOD-FM chassis back to the factory for service.
Please fill in the Registration Card and return it to us.
User Feedback Form: We are very interested in your comments about this product.
Your suggestions for improvements to either the product or this manual will be
carefully reviewed. A User Feedback Form is provided for your convenience. If it is
missing, please write us at the address on the title page. Thank you.

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8100A/1
.Serial # Model #
Name and/or Title
Organization
Street
City/State/Country
Phone #
Zip or Mail Code
Purchased from.
City
Date of Purchase
Nature of your application
How did you hear about it?
Comments:
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Duplicate Registration Card
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FCC Filing (U.S.A): A verification has been filed with the Commission that the
stereo generator t --------- — ... —
If all keys are lost, you can obtain access by removing the three hex-socket screws
from the top of the main front panel with a 5/64" hex wrench (one was supplied with
the unit).
‘ section of OPTIMOD-FM Model 8100 A/l meets all requirements of
FCC 73.322 when used with a direct-FM exciter originally designed with sufficient
bandwidth to accept a stereo generator. As of this writing, there is no requirement
that the FCC be notified that you have changed stereo generators.
Security (Keys and Locks): To control access to the setup controls, the access door
is fitted with a lock. Two keys are supplied. These can be duplicated as desired.
If you wish to make the unit ’ s adjustments more secure, obtain similar splined-socket
or aircraft tri-point screws (and tools), and use these in place of the hex-socket screws
supplied. (Tools for these are not commonly found in hardware stores or other places
D.J. ’ s might frequent.) The screws are 6-32 x 3/8" 82° flathead, nickel-plated steel.
The dealer from whom your 8100A/1 was purchased can supply additional keys, as can
the factory. In either case, your Registration Card must be on file at the factory, and
you must supply your serial number to obtain replacement keys.

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Briefly, the OPTIMOD-FM system performs the following functions:
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5. OPTIMOD-FM generates a stereo baseband signal with outstanding separation, low
crosstalk, and vanishingly low distortion and spurious components.
PARTI:
Introduction
Optional accessories for the OPTIMOD-FM provide for separate studio and main
chassis (8100A/ST), six-band limiting (8100A/XT), and special filtering (Accessory Kit
22). These accessories are discussed in greater detail at the end of this part of the
Operating Manual.
OPTIMOD-FM should be fed unprocessed audio. NO OTH R AUDIO PROC SSING IS
N C SSARY, OR D SIRABL .
4. OPTIMOD-FM prevents peak overload and overmodulation due to the effects of
the FM preemphasis curve.
3. When OPTIMOD-FM's dual-band compressor is operated in "independent ” mode,
OPTIMOD-FM can make audio quality more consistent by correcting frequency
balances between bass and midrange material. When operated in "wideband" mode,
OPTIMOD-FM will preserve frequency balances and will produce an output which
sounds almost precisely like its input.
Function of OPTIMOD-FM: OPTIMOD-FM is an integrated signal-processing system
which replaces conventional compressors, limiters, clippers, and stereo generators.
ach part of the OPTIMOD-FM system has been precisely engineered to be compatible
with all other parts to achieve optimum performance.
2. It prevents aliasing distortion in the stereo generator by means of bandwidth 
limiting 15kHz lowpass filters. Full overshoot compensation is provided for these
filters. OPTIMOD-FM thus provides extremely tight control over peak modulation,
preventing overmodulation and controlling the baseband spectrum simultaneously.
1. It rides gain over a range of as much as 25dB, compressing dynamic range and
compensating for gain riding errors on the part of operators. The amount of dynamic
range reduction ordinarily produced is adjustable. When OPTIMOD-FM is operated
with an optimum release time setting, gain riding and compression are virtually
undetectable because of advanced program-controlled time constants and multiband
compression.

COUPLING
)r
BASS
CROSSOV R
n.
6
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ST R O COUPLING
i \
CROSSOV R
BASS COUPLING
RIGHT OUTPUT
■9
Fig. 1-1: OPTIMOD-FM Model 8100A/1 Signal Flow Diagram
/ *
\ *
BASS
COMPR SSOR
RIGHT
INPUT
L FT
INPUT
INPUT >
CONDITIONING
FILT R >
W
MAST R
COMPR SSOR
MAST R
COMPR SSOR
BASS
COMPR SSOR
HILB RT-
TRANSFORM
CLIPP R
FCS
OV RSHOOT
COMP NSATOI
H-
OV RSHOOT ) L,N
COMP NSATOR AMPLIFI R /
r
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-L-,
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I u PR - MPHASIS?
PR - MPHASIS^
HF LIMIT R ;
J atojfier left output
HF LIMIT R /
HILB RT- \
TRANSFORM ,
CLIPP R /
INPUT \
CONDITIONING
FILT R y

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1-3
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SIMPLIFIED
SYSTEM
DESCRIPTION
The release time of the "Master ’ 1 band only is adjusted with the R L AS TIM
control, thus permitting loudness/fatigue tradeoffs according to format requirements.
Both "Master" and "Bass" compressors are gated such that the release time is slowed
by a factor of approximately 50:1 when the input level drops below a threshold
adjustable by the GAT THR SHOLD control. This prevents noise rush-up during
program pauses, and makes the 25dB gain reduction range usable. Simultaneously,
the gain does not get "stuck" forever, so low-level musical passages are eventually
increased in level. Since gain recovery takes over one minute to occur in GAT D
mode, the gradual increase in level cannot be perceived.
ven in "wideband" mode, the bass control loop is still active. Therefore, heavy bass
will cause a momentary reduction in the gain of the "Bass" band rather than forcing
true wideband system), thus avoiding
Gain reduction in both "Master" and "Bass" compressors is metered by edgewise 
reading meters calibrated with a dB-linear scale. To provide best value, no attempt
has been made to make these meters extremely accurate, and their readings may
disagree with the actual gain reduction by a much as +20%. This accuracy is fully
adequate for the purpose, since the amount of gain reduction varies widely with
variations in program material and operator gain riding.
1. Input Conditioning Filter: This consists of an allpass phase scrambler to make
peaks ’ more symmetrical (thus reducing clipping distortion and permitting higher
loudness), and a 30Hz 18dB/octave highpass filter to prevent subsonic information
from disturbing the operation of the audio processing or exciters' AFC's. ven if an
AFC doesn't unlock, it can attempt to "track" subsonic information, thus producing
IM distortion. The 30Hz highpass filter can be defeated (although we have purposely
made it slightly inconvenient to do so); the phase scrambler is an essential part of
the system and is non-defeatable.
gain reduction of the entire signal (as in a
pumping.
The threshold of limiting is adjustable over a 6dB range by the CLIPPING control.
This determines the output level of the compressor, and thus the amount of HF
limiting and clipping which occur later in the system.
2. Dual-Band Compressor: This consists of two compressors in parallel: "Bass"
which processes audio below below 200Hz (12dB/octave crossover), and "Master"
which processes above 200Hz. A BASS COUPLING control adjustable by the user
determines if the two bands will operate discriminately ("independent" mode), or if
the "Bass" band will be forced to track the "Master" band ("wideband" mode), thus
preserving frequency balances. Intermediate partial-crosscoupling settings are also
available.
OPTIMOD-FM Model 8100A/1 consists of six basic blocks. See cover and figure 4-5
for illustration of controls.
Time constants and other parameters of the Dual-Band Compressor have been
adjusted so that the summed and preemphasized output of the two bands can be
connected directly to the FM Smart Clipper^^. No further gain reduction is
required for distortion control, and maximum naturalness is preserved.

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The threshold of limiting of the high frequency limiter is user-adjustable over a 3dB
range, permitting brightness and high frequency distortion to be traded off according
to format requirements. Because the FM Smart Clipper incorporates IM distortion
cancellation, substantially more clipping can be accomplished without objectionable
distortion than in the old Model 8000A, and significantly improved high frequency
power handling capability is achieved through the system.
4. FM Smart Clipper: The Smart Clipper provides the peak limiting function, and
contains filters to assure that the clipping does not introduce out-of-band frequency
components above 19kHz which could cause aliasing distortion.
The 2.2kHz distortion-cancelling lowpass filter has a time delay. To assure proper
distortion cancellation, the main clipped signal must be delayed by an equal amount
before the main signal and distortion-cancelling signal are added. The main signal is
delayed by a phase-corrected 15kHz lowpass filter, which also removes all out-of-
band harmonics caused by the clipping process.
3. Preemphasis And High Frequency Limiter: The summed outputs of the two
compressors are applied to a phase corrector, 24dB/octave 15kHz lowpass filter,
preemphasis network, and high frequency limiter. The purpose of the lowpass filter
is to prevent out-of-band components from affecting the operation of the high
frequency limiter and to avoid intermodulation between out-of-band frequency
components and in-band frequency components in the clipper. Phase correction
reduces the peak level increase caused by filter ringing and preemphasis to the
theoretical minimum, thus reducing the amount of clipping.
The output of the HF limiter is applied to a clipper with automatically-varying
threshold. This clipper performs the basic peak limiting function. The output of the
clipper is subtracted from its input, thus deriving the distortion added by the
clipper. This distortion component is lowpass filtered at 2.2kHz (the knee of the
75us preemphasis curve), and then added to the clipped signal. This "smoothing
signal" cancels all clipper-induced distortion below 2.2kHz by 30dB or more, and is
particularly effective in eliminating the effects of high-frequency IM, such as
sibilance splatter.
The FCS circuit first derives that part of the signal exceeding the 100% modulation
point by means of a "center clipper". If these overshoots were then subtracted from
— in fact, doing so would be
The high frequency limiter is controlled by high frequencies only (rather than by the
peak level of the preemphasized signal, as in the old Model 8000A), thus eliminating
any possibility of modulation of high frequency content by low frequency material.
the input signal, the overshoots would be cancelled
equivalent to simple clipping. Unfortunately, this can't be done because the
overshoots contain out-of-band frequency components which would cause aliasing
distortion if applied directly to the stereo generator.
5. Frequency-Contoured Sidechain (FCS) Overshoot Corrector: The output of
the Smart Clipper contains overshoots due to the addition of the distortion 
cancelling signal, and due to unavoidable overshoots in the 15kHz filter. These
overshoots must be eliminated without adding out-of-band frequency components.
This is done in the FCS Overshoot Corrector.

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The overshoot filter has phase shift. Phase shift networks are therefore included in
the main path to make sure that the overshoot subtraction process works correctly,
and that the overall FCS system has constant time delay.
Because the FCS circuit is an instantaneous system and uses no gain reduction or
dynamic filtering, it causes neither pumping nor dulling of program material.
We therefore lowpass-filter the overshoots to eliminate out-of-band components. If
the overshoot filter had a flat response to its cutoff frequency, this filtering action
would reduce the amplitude of high-frequency overshoots (by removing out-of-band
harmonics which make the overshoots "spikey"). This would result in incomplete
cancellation of the overshoots after subtraction. The overshoot filter is therefore
designed to have a rising response at 15kHz, effectively increasing the gain of the
fundamentals of the higher-frequency overshoots and compensating for the fact that
their harmonics have been removed. The overshoot extractor and this filter are the
’ ’ Frequency-Contoured Sidechain".
The rising response of the overshoot filter means that essentially no extra
subtraction gain (compared to the system operated without the filter as a simple
differential clipper) is required. Any low frequency IM introduced by the FCS circuit
is therefore no worse than the low-frequency IM caused by a simple clipper.
6. Stereo Generator: The stereo generator accepts the processed outputs from the
left and right FCS circuits, and produces the stereo baseband signal. It is
characterized by high stability, very low distortion, and minimal spurious outputs.
19kHz oscillator level, pilot phase, and separation are all controlled and stabilized
by means of servo loops.
To facilitate adjustment of pilot phase and measurement of main-channel-to-
subchannel and subchannel-to-main-channel crosstalk, two special T ST modes are
provided. These apply the right channel audio directly to the main or sub inputs of
the stereo generator. For testing, these stereo generator audio inputs can be
accessed by means of a pair of T ST jacks on the rear chassis apron. This provides
an alternate means of measuring crosstalk and other stereo generator performance
parameters.
The stereo baseband is generated by the "matrix" technique, as opposed to the more
common "switching" design. The "matrix" design modulates only the L-R component,
and passes the L+R component through to the output without degradation due to
switching. Since the L+R component almost always dominates, this results in
maximum audio quality. In addition, no baseband lowpass filter is required. Such a
filter would add to system cost, and could compromise separation.
The stereo generator can be operated in ST R O, MONO L FT, or MONO RIGHT
modes. All three modes can be selected by remote control by means of optically-
isolated remote control terminals. ST R O and one of the two MONO modes can be
selected locally by means of a front-panel switch. An internal strap determines
which of the two MONO modes is selected. Another internal strap determines which
of the three modes will be entered on powerup.

Finally, the +15 and -15V power supply voltages are monitored.
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VU Meter: The front-panel VU meter can monitor the level of the left and right
audio at three different points in the circuitry. (See Block Diagram [p. J-21] for
metering points.) The meter also monitors the difference between left and right
channels (L-R) to aid channel balance adjustments.
Three stereo generator parameters are monitored: 19kHz pilot oscillator level,
38kHz AGC control voltage, and 38kHz Phase-Locked Loop control voltage. The
latter two readings will vary, and are used to check whether these servo loops are
within their ordinary operating range, or whether they are saturated.

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Accessories Currently Available:
(A separate manual is supplied with this unit.)
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(A separate manual is supplied with this unit.)
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— ’ Increased presence and intelligibility on smaller radios and in autos.
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More complete information about the 8100A/ST is provided in a separate manual
shipped with the unit.
Functionally, the unit replaces the high frequency limiter within the 8100A/1 and
permits the following objectives to be met:
8100A/ST
STUDIO ACCESSORY
CHASSIS
8100A/XT
SIX-BAND LIMITER
ACCESSORY
CHASSIS
The optional 8100A/XT Accessory Chassis has been created to provide aggressive
multiband processing for stations that desire bright, loud, ’ ’ highly-processed" audio.
Derived from OPTIMOD-AM Model 9100A, 8100A/XT consists of a stereo bass
equalizer which drives a stereo six-band limiter cascaded with the exclusive Orban
distortion-cancelling multiband clipping system. When added to the basic 8100A/1
system, the 8100A/XT creates a dense, consistent sound without pumping or other
obvious processing artifacts.
— Improved consistency from source to source due to the "automatic equalization"
effect of the six-band limiter; and,
The Accessory Chassis provides convenient access at the studio to all operating
controls except for H-F Limiting and stereo/mono mode switching. It provides the
same gain reduction metering as the Main Chassis, and several diagnostic metering
functions as well.
The 8100A/XT is most appropriate for contemporary popular music formats, although
its ability to improve consistency and intelligibility can make it useful for talk and
news formats as well. It is generally unsuited for "beautiful" or classical formats.
In some installations, it may be desirable to perform the compression function ahead
of the STL to optimize system signal-to-noise ratio by relaxing STL headroom
requirements. (STL ’ s are discussed further in Part 2). The Model 8100A/ST Accessory
Chassis (which performs this function) consists of a chassis shell assembly with a
power supply/metering card and three empty card locations. Cards #3, #4, and #5 (the
Dual-Band compressor cards) are removed from the Main Chassis and installed in these
locations. Dummy cards provided with the Accessory are then installed in the Main
Chassis to preserve the signal path.
The Model 8100 A/1 is prewired to readily accept the 8100A/XT. (Older SlOOA ’ s must
be converted by means of retrofit kit "RET-27" before they can accept the 8100A/XT.)
— For most types of program material, increased loudness for a given level of audible
processing side-effects (by comparison to an unmodified 8100 A/l or 8100 A);

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Card #0 is installed in the signal path between the output of the existing cards #8/9
and the input of card #7 (stereo generator).
typically +0, -O.ldB, 30-15, 000Hz.
perform well within its +0.75dB specification.
The frequency response of the card is
An 8100A/1 containing this card will therefore
Card #0 has been specifically designed to be used in conjunction with the 8100A/l's
existing FCS Overshoot Corrector.
Optimod-FM Model 8000A,
The 8100A/XT is fully compatible with the Studio Accessory Chassis Model 8100A/ST,
allowing use of the 8100A/XT in either single- or split-chassis installations. In all
cases, the 8100A/XT is mounted immediately below the main (8100A/1) chassis.
Card #0 replaces each safety clipper with two cascaded overshoot-compensated
lowpass filters. This reduces "splatter" in the SCA region of the baseband by 25-30dB
compared to the "stock" 8100A, and simultaneously reduces any residual overshoot by
about 5%. This processing can achieve loudness within 0.3dB of that produced by
composite clipping (an inaudible difference), while protecting the SCA region about 40-
50dB better than a composite clipper.
Full instructions for installing and operating the 8100A/XT are included in the
Operating Manual for that unit. That Manual also includes a complete discussion of
the 8100A/XT's principles of operation, how it relates to the 8100A/1, and other
information important to those who plan to use the unit.
ACCESSORY KIT 22: (Separate installation and alignment instructions
FM FILTER CARD (#0)
are included in this kit.)
The normal positions of 8100A/1 card jumpers when the 8100A/XT is not in use
tabulated in Appendix M of this Manual.
The 8100A/XT uses a great deal of the existing 8100A/1 circuitry in the interest of
achieving efficiency and economy. The 8100A/XT (which requires two rack units) is
mounted directly below the 8100A/1 and is then plugged into a multipin connector on
its rear panel. Jumpers on Cards #5, #6, #8, and #9 within the 8100A/1 must then be
moved according to instructions in a manual supplied with the 8100 A/XT.
Card #0 is therefore unusable with our older
or with other manufacturers ’ equipment.
The OPTIMOD-FM Model 8100A/1 has been designed to meet all FCC Rules regarding
crosstalk between the main channel and subchannel and vice-versa. However, higher
performance than this is sometimes desirable to fully protect SCA subcarriers from
interference caused by the operation of the 8100A/l ’ s safety clippers (on cards #8 and
#9) on extremely densely-processed program material.
This concludes the Introduction and Simplified System Description. The next part
of this manual (Application) should now be read carefully to assure that your
installation produces optimum results.

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2-1
PART 2:
Application
This Part of the Manual provides essential information on how OPTIMOD-FM fits in
with the rest of the equipment at your station. Appendix K contains further
information on achieving high audio quality.
All except (3) carry both audio channels either directly, or in some encoded form other
than the standard 19kHz "pilot tone" stereo baseband. These links are ordinarily fed
both left and right audio channels in non-encoded form, and their receiver output is
the regenerated left and right channels.
The composite STL (3) carries the standard "pilot tone" stereo baseband, and is
therefore fed from the output of a stereo generator like the one in the 8100A/1. The
receiver output of the composite STL is the stereo baseband signal, which is applied
directly to wideband input of the FM broadcast transmitter ’ s exciter.
PCM links are generally unavailable in the USA as of this writing, although they are
widely used in Europe. They achieve good noise performance and consistency at the
expense of a very sharp high-frequency cutoff, rapid changes in group delay around
cutoff (unless elaborate phase equalization is used), and quantization distortion. At the
moment, there is considerable disagreement over how elaborate the coding must be to
render quantization distortion inaudible to critical listeners, and no PCM system should
be accepted without critical listening tests.
1) Analog land-lines (telephone lines)
2) Dual-microwave STL's
3) Composite baseband microwave STL's
4) PCM (Pulse-Code Modulation) links
5) Video STL's with PCM adapters
Land-line quality is extremely variable, ranging from excellent to atrocious. The
decision on whether to employ land-lines depends a great deal on the quality locally
available. However, even the best land-lines tend to slightly veil audio quality due to
line equalizer characteristics, phase shifts, and repeaters of indifferent quality.
Some stations are sending PCM-encoded audio through a video STL at frequencies
above 20GHz. Typically, consumer PCM adapters (from Sony or dbx, for example) are
being used. The quality of signal received at the transmitter through this type of STL
is high.
Studio/Transmitter Links: There are five types of studio/transmitter links in common
use internationally in FM stereo service. These are:
The dual-microwave system provides more noise immunity. However, problems include
gain- and phase-matching of the left and right channels, preemphasis-induced
overloads, and requirements that the audio applied to the microwave transmitters be
processed to prevent overmodulation.
In general, highest quality is obtained by use of a composite microwave STL provided
that a line-of-sight transmission path of less than 10 miles or so exists between studio
and transmitter. If not, RF signal-to-noise ratio, multipath distortion, and diffraction
effects can cause serious quality problems.