Orban OPTIMOD-FM 8100A/XT2 User manual

Operating Manual
OPTIMOD-FM
Six-Band Limiter
MODEL 8100A/XT
An Accessory for OPTIMOD-FM Model 8100A/1
•» A
95057-000-01 1/87

APPARENT MODULATION OF PILOT IN THE 8100A
by Robert Orban
Chief Engineer
Orban Asso iates, In .
Apparent modulation of the pilot is often observed on a stereo monitor
whi h is monitoring an 8100A-pro essed signal. This modulation may be
real, or it may be a measurement artifa t — it is almost always the latter.
To a urately indi ate pilot level, the pilot must be extra ted from
the baseband signal by means of a highly sele tive bandpass filter in
the monitor. The pilot is typi ally 21dB below 100% modulation. When
bright program material is en ountered, the ombination of the 8100A's
ex ellent high frequen y power handling apability and the 75us pre 
emphasis urve will result in energy lose to 100% modulation in the
frequen y range immediately adja ent to the pilot. If the monitor's
pilot extra tion filter is insuffi iently sele tive, enough of the pro 
gram energy an leak into the filter to ause apparent modulation of
pilot level when observed on the monitor's meter. This is a linear ef 
fe t, and is aused solely by inadequate filtering.
A similar problem an o ur if a spe trum analyzer is used. The spe 
trum analyzer uses a sele tive swept filter. If the sele tivity of the
filter is adjusted too broadly, then the filter will be insuffi iently
sele tive to distinguish the pilot from the immediately adja ent high-
level program material. In general, this is aused by attempts to use
an ex essively fast sweep rate.
Using a Tektronix 5L4N Spe trum Analyzer in our laboratory, this phe 
nomenon was observed at faster sweep rates. At a sweep rate of 10kHz/
se , it was possible to narrow the sele tivity of the filter to the
point where the pilot was learly seen to be some 50dB above any a tual
program material in the 19kHz region. This is su h a great degree of
separation between pilot and interfering signal that the maximum amount
of effe tive modulation of the pilot would be approximately ;+0.3% of
the pilot inje tion, or +0.027% modulation. Sin e pilot inje tion is
permitted by FCC rules to vary within 8 to 10% modulation, this tiny
amount of modulation is entirely trivial. However, it must again be
stressed that this an only be measured with a orre tly operated spe 
trum analyzer: the bandpass filters in typi al stereo monitors or in a
fast-sweeping spe trum analyzer are insuffi iently sele tive.
Non-linear effe ts in other parts of transmission or measurement system
an result in modulation of the pilot whi h annot be eliminated by or 
re t filter bandwidth. Ex iter non-linearity is suspe t; narrowband RF
amplifiers and antennas and/or ex essive VSWR an also ause problems.
ont'd.
Orban Associates Inc. 645 Bryant Street San Francisco, A 94107
Main: [phone] Sales: [phone] Telex: 17-1480 able: orbanaudio

In addition, any off-the-air pilot modulation measurements are them 
selves suspe t be ause intermodulation between the pilot and high-
energy high-frequen y program material is very sensitive to multi 
path — even in amounts whi h do not ause the ustomary multipath in
di ators to respond. Therefore, the FCC annot a urately monitor
this parameter off-the-air. It must be done from the monitor sample
point of the transmitter using a highly linear demodulator and a
slow-sweeping spe trum analyzer.
In summary: The extra high frequen y energy permitted by 8100A pro 
essing may reveal limitations of ustomary pilot measurement.te h 
niques. Spe trum analysis in our laboratory has onfirmed that the
pilot in the 8100A is more than adequately prote ted, provided that
the filter ir uitry in ards #8 and #9 is operating a ording to
spe ifi ations. While real modulation of the pilot an be aused by
non-linearities in ex iters and the RF path following, the probabil 
ity is high that measurement te hniques are at fault.
RO: kt

8100A/XT2 SIX-BOND LIMITER FINAL TEST
Date: 4 — 13 — 07 S/N: 9861
Technician: DDM
1. OVERALL DEEMPHASIZED FREQUEN Y
RESPONSE, 35 — 15k Hz
Left : + .41,
-. 36dB / Right: + . 45, -. 50dB
S. TOTAL DEEMPHASIZED HARMONI DISTORTION
(Measured in TEST mode @100% modulation
and in OPERATE mode with controls per
NOTE 2 (below)
LEFT RIGHT
FREQ.
TEST OP TEST
OP
50
. 057%
. 095% . 035% .091%
100 . 059%
. 066% . 040%
. 061%
400 . 047% . 039% . 052% . 039%
1000
. 031% . 038%
. 024%
. 040%
5000 . 081% . 045% . 037%
. 043%
10000
. 051% . 059% . 048%
. 058%
15000 . 068% . 066%
. 066% . 064%
3. NOISE (deemphasized: dB below 100"/.)
Left: — 82. 8dB Right: -83. 6dB
NOTE 1: Measurements made through
Hewlett-Packard 8903A
omputerized Audio Analyzer
NOTE 2: ontrol Settings For Operate-Mode THD Test
MAIN HASSIS:
L&R INPUT OTTENS: 0
LIPPING: +2
RELEASE TIME: 10
BOSS OUPLING: 10
GATE THRESH: 0
HF LIMITING: 5
XT HASSIS:
BASS EQ (L&R) : 0
DENSITY: 5
LIPPING: -4
PRESEN E EQ 0
BRILLIAN E EQ 0
BOORD SERIAL NUMBERS:
Board #A 1 :
Soard #A 2 : 7
loard #0 3 :

Section 1
General Information
In this section:
1. How to Use This Manual
(Table of Contents) this pa e
2. Re istration, Warranty, Feedback pa e 1-2
3. Index 1-3
4. The XT2 Six-Band Limiter 1-4
5. Simplified Description of the 8100A/1 + XT2 System 1-5
6. Interface with OFT'IMOD-FM 1-6
1. HOW TO USE THIS MANUAL
This manual has six sections:
Section 1: General Information
Section 2: Installation
Section 3: Operating Instructions
Section 4: Maintenance and alibration
Section 5: Troubleshooting
Section 6: Technical Data
Each section has a Table of Contents. In addition, a comprehensive INDEX (on pa e 1-3)
covers the entire manual.
This GENERAL INFORMATION section provides an overview of the product and its
application. For complete installation instructions, see the INSTALLATION section.
Performance verification procedures are in the MAINTENANCE AND CALIBRATION
section. See the TROUBLESHOOTING section for information on technical support,
factory service, and shippin .
The TECHNICAL DATA section contains specifications, circuit descriptions, parts lists,
and schematics. Throu hout the circuit descriptions, keywords are hi hli hted to help you
quickly locate the information you need.
In this manual “ XT2 ” is used to mean “ 8100A/XT2 Six-Band Limiter Accessory Chassis ” .
“ OPTIMOD-FM ” and “ 8100A/1 ” are used interchan eably to refer to the “ OPTIMOD-FM
Model 8100A/1 ” (or “ OPTIMOD-FM Model 8100A modified with Retrofit Kit RET-27 to
function as an OPTIMOD-FM Model 8100A/1 ” ) except where the context clearly indicates
otherwise. To ether the OPTIMOD-FM and XT2 form the “ 8100A/1 + XT2 System ” .
This manual is intended to be used in conjunction with the Operating Manual for the
OPTIMOD-FM® Model 81 AH.

1- General Information
. REGISTRATION, WARRANTY, FEEDBACK
Re istration Card
There are two ood reasons for returnin the Re istration Card shipped with this product:
1) It enables us to inform you of new applications, performance improvements, and service
aids which may be developed, and
2) It helps us respond promptly to claims under warranty without havin to request a copy
of your bill of sale or other proof of purchase.
Please fill in the Re istration Card and send it to us today. If it is lost (or you have purchased
this unit used), please photocopy the duplicate below, fill it in, and send it to Orban at the
address on the title pa e.
Model # Serial #
Name or Title
Organization ______________________________________________________________________
St reet
ity/State/ ou ntry --------------------------------------------------------------------------------------------------------------
Zip or Mail ode
Purchased from ity Date of Purchase
Nature of your application _
How did you hear about it? _
om ments: __________________ .
Warranty
The warranty, which can be enjoyed only by the first end-user of record, is stated on the
Warranty Certificate on a separate sheet packed with this manual. Save it for future reference.
Details on obtainin factory service are provided in Section 5.
User Feedback Form
We are very interested in your comments about this product. Your su estions for improve 
ments to either the product or the manual will be carefully reviewed. In the back of this
manual, a postpaid User Feedback Form is provided for your convenience. If it is missin ,
please write us at the address on the inside of the front cover. Thank you.

General Information 1-3
3. INDEX
8100A 1-6, 2-2
8100A/1 1-1, 1-6, 2-2, 6-3
81 00A/1 + XT2 System 1-1
81 OOA/ST 1 -6, 2-2, 2-6, 2-12, 4-2
A -22 FM Filter ard 1 -5, 3-7, 3-9
accessory port 2-8, 6-3
automatic gain control (AG ) 6-6
brightness 3-4
brilliance 1-4,3-7
circuit cards
access to 4-1
#A1 6-5,7, 6-10, 6-12
#A2 6-9, 6-24
#A3 4-9, 6-7, 6-26
#PS 2-7
#5 2-4, 2-8, 5-5, 6-30
#6 2-4,2-10,6-5
#8, #9 2-5,2-11,6-5,6
circuit description 6-3
clipping 3-6,7, 6-9
main clipper defeat 6-5
safety clipper 6-5
compression 3-6, 6-3
connections 2-5
consistency 1-4
crossovers 6-2, 6-7, 6-10
controls 3-1, 6-3,4,5, 6-9
recommended settings 3-5
customized settings 3-6
customer service 5-6
de-installation 4-14
density 3-6, 6-4
dimensions 6-2
distortion 1-5, 3-4, 3-7,8, 5-3,4, 6-2, 6-4, 6-8
-cancellation 4-7, 6-4,6, 6-10
N&D 4-5
sibilance 5-3
THD 6-2
V A 4-10
dual-band compressor 6-3
equalization
automatic 1 -4
bass 1-4, 3-8, 6-2, 6-3, 6-5
dynamic re- 3-6
high-frequency 1 -4, 3-7
F S Overshoot ompensator 6-3, 6-5,6
field alignment 4-9
field audit of performance 4-2
FM Filter ard A -22 1 -5, 3-7, 3-8
format 1-4,3-4
frequency response 4-5, 6-2
frequency balance 5-3
functional description 6-3
HF filter 6-5
installation 2-3
de-installation 4-14
intelligibility 6-4
intermodulation 6-4,6-10
jumpers 2-3
limiting 3-6, 6-2, 6-3, 6-6, 6-9
loudness 1-4, 3-4, 3-6,7, 6-4
maintenance 4-1
meters 3-2, 4-7, 6-3
modulation 6-6
mounting 2-5
noise 5-4, 6-2
noise reduction modification 5-5
openness 3-4
OPERATE mode 4-6, 6-6
OPTIMOD-FM 1-1
parts list 6-12
ordering parts 6-12
performance 4-6, 6-2
verification 4-2
power requirements 6-2
presence 1-4,3-7
product overview 1-4,5
PROOF mode 6-3, 6-5
pumping 5-4
registration card 1-2, 2-5
retrofit RET-27 instructions 1-6, 2-6
removing XT2 from operation 4-14
service 5-7
shipping
damage 2-3
instructions 5-7
six-band limiter 3-6, 6-2, 6-3, 6-6, 6-9
sound quality problems 5-3
sound texture 3-4
source material 3-8, 6-4
specifications 6-2
Studio hassis 1-6, 2-2, 2-6, 2-12, 4-2
technical support 5-6
telephone speech 6-4
THD 4-5, 4-6, 6-2
time constants 6-3
troubleshooting 5-1
user feedback form 1 -2
V A 6-5
calibration
gain control
thump null
4-12
6-7
4-12, 6-8
warranty 1 -2
XT2 1-1, 1-4

1-4 General Information
4. THE XT SIX-BAND LIMITER
The Orban Model 8100A/XT2 Six-Band Limiter Accessory Chassis was desi ned for those
stations that need a “ louder ” or more processed sound than that provided by an OPTIMOD-
FM used alone and in the recommended manner. The XT2 provides the means to fine-tune
your on-air sound throu h precise control of bass and treble sound texture, pro ram density,
and pro ram dynamics.
The XT2 is desi ned to ive you:
- Increased loudness for a iven level of audible processin side-effects (compared to an
unmodified 8100A/1).
- Improved consistency from source to source, due to the “ automatic equalization ” effect
of the six-band limiter.
- Increased presence and intelli ibility on smaller radios and in autos.
- Control of bass and hi h-frequency equalization.
The XT2 is particularly well-suited for hi hly competitive pop music formats, such as AOR,
CHR, AC, and Urban Contemporary. Oldie and Beautiful formats can also benefit from
the improved consistency that the XT2 ’ s “ automatic equalization ” can provide. Because it
has been specifically “ tuned ” to the OPTIMOD-FM, it produces less processin side-effects
than do complex processin systems that use OPTIMOD-FM cascaded with other processors.
(The XT2 cannot be used with other audio processors or as a stand alone unit.)
In eneral, the 8100A/1 + XT2 System will be only sli htly louder than an 8100A/1 alone,
operated with very fast release times and lar e amounts of clippin . This is because the
loudness capabilities of an audio processor system are primarily determined by the desi n of
the peak-limitin system, and the XT2 ’ s peak-limitin system is very similar to the hi hly
sophisticated, patented system used in the 8100A/1.
Any loudness increase produced by the XT2 results from two characteristics: 1) tire XT2 can
automatically re-equalize dull pro ram material, increasin ener y in the frequency ran e to
which the ear is most sensitive, and 2) XT2 processin reduces voice level by comparison
to music. Since the clippin level in a processor system must often be set to avoid audible
voice distortion, the XT2 permits the processor to be adjusted to produce hi her loudness on
music before voice distortion becomes objectionable.
Because of the XT2 ’ s “ automatic equalization ” of pro ram material, there is some material
(notably “ heavy metal ” with extreme amounts of 3kHz ener y) which will actually be quieter
throu h the XT2 than throu h the 8100A/1 alone because the amount of 3kHz ener y (to
which the ear is maximally sensitive) will be reduced by the XT2.
The primary advanta es of the 8100A/1 + XT2 System are improved consistency, increased
bri htness on naturally dull pro ram material, and reduction of audible processin side effects
— all while retainin or sli htly exceedin the hi h loudness capabilities of an a ressively
operated 8100A/1.

General Information 1-5
5. SIMPLIFIED DESCRIPTION OF THE 8100A/1 + XT SYSTEM
The 8 100A/1 and the XT2 combine to form an inte ral system. Functionally, the XT2 adds
bass equalization, six-band limitin , hi h-frequency equalization, and multiband distortion 
cancellin clippin to the 8100A/1.
In the 8100A/1 + XT2 System, the 8100A/l ’ s dual-band compressor is used to maintain
constant levels into the XT2 ’ s six-band limiter. This prevents excessive six-band limitin
(which can result in unpleasant increases in density), while ensurin that desirable amounts
of limitin occur consistently. The 8100A/l ’ s release time control adjusts the speed of the
dual-band compressor ’ s response. Settin s toward SLOW cause the compressor to ride ain
like a “ slow hand on the pot ” , not affectin short-term density or texture. Settin s toward
fast result in a more consistently loud sound with increased density.
The dual-band compressor is also used as a dynamic bass equalizer to control the “ warmth ” of
the sound. The 8100A/l ’ s BASS COUPLING control adjusts this broadband bass equalization.
In addition, the XT2 ives the si nal a bass boost to compensate for the increased bri htness
often added by the six-band limiter. The boost frequency has been chosen to create very
“ punchy ” bass, particularly on speakers with reasonably extended bass response. BASS eq
controls adjust the amount of bass “ punch ” the XT2 adds to each channel.
The XT2 divides the si nal into six bands by a set of filters. Separate presence and bril 
liance controls adjust the drive levels into the two hi hest bands, enablin use of the XT2
as a dynamic hi h-frequency equalizer.
The use of six bands of limitin permits si nificant correction of midran e frequency balances
and production of a more consistent, intelli ible, and pleasin sound. Individual limiters for
each of the six bands make the XT2 capable of far more fast ain control without audible
side effects than would be possible with the dual-band compression used in the 8 100A/1 .
Loudness is increased by reducin the peak-to-avera e ratio of the audio, so the avera e level
can be increased within the modulation limits permitted. The peak-to-avera e ratio of the
six-band limiter ’ s output is reduced by distortion-cancellin clippin and filterin . This also
allows the si nal to be applied to a final safety clipper (in the 8100A/1) without the need for
further broadband ain control, which could introduce pumpin and modulation effects.
The output of the safety clipper is returned to the 8100A/1 ’ s stereo enerator, which produces
the stereo baseband si nal.
(If maximum loudness combined with improved spectral protection of the SCA re ion of the
baseband is desired, the safety clippers in the 8100A/1 can be replaced with the optional FM
Filter Card, available as Accessory Kit ACC-22.)
For a more detailed description of XT2 circuitry, see Section 6.
For more information about 8100A/1 circuitry, see the 8100A/1 Operatin Manual.

1-6 General Information
6. INTERFACE WITH OPTIMOD-FM
The XT2 interfaces with the Model 8 100A/1 OPTIMOD-FM throu h a cable which connects
to the 8100A/l ’ s Accessory Port #2. The XT2 receives its power from the host 8100A/1,
and should always be mounted immediately beneath the host. To reconfi ure the 8100A/1
for operation with the XT2, it is only necessary to move plu -in jumpers on certain circuit
boards (see Section 2). Reconvertin an 8100A/1 to operate without the XT2 is as simple as
repositionin those jumpers (see Section 4).
The earlier Model 8100A can be easily converted to accept the XT2 by installation of Retrofit
Kit RET-27, available from dealers or from the factory. This kit includes a prewired 25-pin
connector, a replacement Card #5, and other parts. RET-27 installation instructions are
included in Section 2. Instructions for reconvertin an 8100A for use without the XT2 are
iven in Section 4 (some solderin is required).
The 8100A/ST Studio Accessory Chassis (used to implement the “ split ” studio/transmitter
confi uration) is fully compatible with the XT2.

Section 2
Installation
In this section:
1. WHAT TO DO Read this first! pa e 2-2
2. Installation Instructions 2-3
1) Unpack and inspect. 2-3
2) Reposition jumpers on OPTIMOD-FM Cards. 2-3
Fi . 2-1: Jumper Positions, Card #5 2-4
Fi . 2-2: Jumper Positions, Card #6 2-4
Fi . 2-3: Jumper Positions, Cards #8 and #9 2-5
3) Mount and connect XT2. 2-5
4) Return Re istration Card. 2-5
5) Set 8100A + XT2 System Controls. 2-6
3. Retrofit Instructions 2-6
1) Open the OPTIMOD-FM ’ s front panel, remove subpanel. 2-6
2) Check, add resistors on OPTIMOD-FM Card #PS. 2-7
3) Install accessory port in OPTIMOD-FM. 2-8
4) Check, replace OPTIMOD-FM Card #5. 2-8
Fi . 2-4: Accessory Port #2 Installation 2-9
5) Check, rework the OPTIMOD-FM Card #6. 2-10
Fi . 2-5: Card #6 Rework 2-11
6) Check, rework OPTIMOD-FM Cards #8 and #9. 2-11
4. XT2 with the Studio Chassis Accessory 2-12
Fi . 2-6: Studio Chassis Jumper Positions, Card #5 2-13
AUTION
The installation and servicin instructions in this manual are
for use by qualified personnel only. To avoid electric shock
do not perform any servicin other than that contained in
the Operatin Instructions unless you are qualified to do so.
Refer all servicin to qualified service personnel. (perutsia)

-
Installation
1. WHAT TO DO
READ THIS FIRST!
If you are installin an 8100A/ST Studio Chassis, read XT2 WITH THE STUDIO CHASSIS
ACCESSORY at the end of this section before installin either unit.
The XT2 itself merely needs to be mounted in a rack and connected to the host OPTIMOD-
FM Audio Processor. However, certain jumpers on the host OPTIMOD-FM ’ s circuit boards
must be repositioned to confi ure the unit for operation with the XT2. In addition, older
OPTIMOD-FM Audio Processors may require simple reworkin of some of their circuit
boards and/or installation of an accessory port.
If your OPTIMOD-FM is Model 8100A/1 with a serial number of 699000 or above, you
need only follow the INSTALLATION INSTRUCTIONS.
(The model and serial number of your OPTIMOD-FM are shown on a rear-panel label.)
If your OPTIMOD-FM is Model 8100A/1 with a serial number below 699000, you must
first perform steps 1 and 2 of the RETROFIT INSTRUCTIONS.
If your OPTIMOD-FM is Model 8100A (serial number below 638000), you must follow
all of the RETROFIT INSTRUCTIONS before installin the XT2.

Installation -3
. INSTALLATION INSTRUCTIONS
Read “ WHAT TO DO ” on the precedin pa e before continuin .
Allow about an hour for installation.
(Installation must be done with the OPTIMOD-FM off-the-air.)
The XT2 should not be installed until the OPTIMOD-FM Audio Processor has been installed
and thorou hly tested on the air.
1) Unpack and inspect.
If you ever re-ship the XT2 (e. ., for servicin ), it is best to ship it in the ori inal packin
materials since these have been carefully desi ned to protect the unit. Make a mental note
of the method of packin and save all packing materials.
Packed with the 8100A/XT2 are:
1) Two 1.8-ohm resistors (for step 2 of RETROFIT INSTRUCTIONS)
2) Four 10-32 x 3/4 ” screws (for rack mountin )
3) Two keys for front-panel door
4) Final Factory Qualification Test Results for this unit
5) This Operatin Manual
Perform a eneral inspection of the contents of the packa e to check for obvious dama e.
DAMAGE CLAIMS must be made by you a ainst the carrier immediately upon discovery.
Save packin and other evidence of dama e for the carrier ’ s inspector.
IMPORTANT: Before continuin , you must follow the RETROFIT INSTRUCTIONS in this
section if the serial number of your OPTIMOD-FM is below 699000 (see WHAT TO DO on
the precedin pa e). When the retrofit is complete, return to this step.
) Reposition jumpers on OPTIMOD-FM Cards #5, #6, #7, and #8.
a) Open the OPTIMOD-FM ’s front panel, remove subpanel.
Jumpers may be reset from the front of the chassis while the unit is in the rack, once
the front panel has been opened and the subpanel removed.
Remove the three hex-socket screws at the top of the front panel with a 5/64 ” hex wrench
(provided with unit). Tilt the hin ed front panel downward to reveal the interior. Set the
AC POWER switch to OFF. Loosen the four DZUS fasteners on the subpanel by turnin
each one-quarter turn counterclockwise with a lon 3/16 ” or 1/4 ” flat-blade screwdriver.
Takin care not to stress the flat cables beneath it, tilt the top of the subpanel outward
and to the left to clear the upper chassis lip and the door support rail at the ri ht.
AUTION
To avoid trauma to circuit card components, be sure the AC
POWER switch (located behind OPTIMOD-FM ’ s front panel)
is set to OFF before removin or insertin any of the printed
circuit cards.

-4
Installation
b) Remove Card #5. Move each of jumpers A, B, and C to the “ 6-BAND LIMITER
ACCESSORY CHASSIS ” position (see Fi . 2-1). Reinstall Card #5.
Fi . 2-1; Jumper Positions, OPTIMOD-FM Card #5
(For ard #5, part numbers 30741-000-03 and above only — if your card looks
different, see Appendix J of your OPTIMOD- FM Operating Manual for jumper locations.)
c) Remove Card #6. Move the two links at jumper C to jumper B (see Fi . 2-2). DO
NOT MOVE jumper A. Reinstall Card #6.
Fi . 2-2: Jumper Positions, OPTIMOD-FM Card #6
(For ard #6, part numbers 30461-000-03 and above only — if your card looks
different, see Appendix J of your OPTIMOD-FM Operating Manual for jumper locations.)

Installation
-5
d) Remove Cards #8 and #9. On each of Cards #8 and #9, move the link at jumper B
to the “ ACCESSORY CHASSIS ” position (see Fi . 2-3). DO NOT MOVE jumper A
on either card. Reinstall the cards.
Fi . 2-3: Jumper Positions, OPTIMOD-FM Cards #8 and #9
(For ards #8/#9, part numbers 30481-000-04 or above only — if your cards look
different, see Appendix J of your OPTIMOD-FM Operating Manual for jumper locations.)
e) Reinstall the OPTIMOD-FM ’ s subpanel and close the front panel.
Takin care not to stress the flat cables beneath it, tilt the top of the subpanel inward
and to the left to clear the upper chassis lip and the door support rail at the ri ht. The
DZUS fasteners turn only 1/4-tum. Don ’ t force them, lest they be dama ed in a way
that is very time consumin to repair. The subpanel should always be replaced since
it is an inte ral part of the chassis RFI protection.
Set the internal AC POWER switch to ON. Raise the front panel and fasten the three
screws that secure it in place. If the unit was removed from the rack, remount it. Ground
the unit and connect AC power.
3) Mount and connect XT .
a) Mount the XT2 in a rack immediately below the OPTIMOD-FM.
The XT2 ’ s connectin cable will not reach the connector on the OPTIMOD-FM unless
the XT2 is mounted directly below the OPTIMOD-FM.
b) Plu the flat cable from the XT2 into the OPTIMOD-FM ’ s ACCESSORY PORT #2
and attach the connector with the retainin screws.
Both power and si nals for the XT2 are supplied throu h this cable.
4) Complete the Registration Card and return it to Orban (please).

-6
Installation
5) Set 8100A + XT System controls.
The OPTIMOD-FM and XT2 work to ether in a system. The controls on one unit affect
the performance of the other. See Section 3 for recommended control settin s and for
information on customizin your audio processin .
If you are usin an 8100A/ST Studio Chassis, set its controls to the settin s recommended
for the 8100 A in Section 3.
3. RETROFIT INSTRUCTIONS
IMPORTANT: Skip these instructions if the serial number of your OPTIMOD-FM is
699000 or above.
If your OPTIMOD-FM is Model 8100A/1 with a serial number below
699000 but not below 638000, follow steps 1 and 2 only.
If your OPTIMOD-FM is Model 8100A (serial number below 638000),
follow steps 1 throu h 6.
Materials: Retrofit Kit RET-27 (available from the factory) contains the parts needed in
steps 3 throu h 6. The resistors specified in step 2 are supplied with the XT2.
These retrofit modifications are simple and require only common circuit board repair skills,
appropriate tools, and a careful, systematic approach. However, to save time and avert
errors, we su est that you read throu h each step in these instructions with board in hand
before be innin work.
The drawin s in Appendix J of your OPTIMOD-FM Operatin Manual show component
locations. (If you have the older 8100A unit, see Section 6 of the this manual for Card
#5 drawin s.) Advice for reworkin printed-circuit cards is iven in Appendix F of the
OPTIMOD-FM manual.
1) Open the OPTIMOD-FM ’ s front panel, remove subpanel.
Remove the three hex-socket screws at the top of the front panel with a 5/64 ” hex wrench
(provided with unit). Tilt the hin ed front panel downward to reveal the interior. Set the
AC POWER switch to OFF. Loosen the four DZUS fasteners on the subpanel by turnin
each one-quarter turn counterclockwise with a lon 3/16 ” or 1/4 ” flat-blade screwdriver.
Takin care not to stress the flat cables beneath it, tilt the top of the subpanel outward
and to the left to clear the upper chassis lip and the door support rail at the ri ht.

Installation
-7
) Check, add resistors on OPTIMOD-FM Card #PS.
Allow about 45 minutes for this step.
a) Check the values of resistors R103 and R104 on the OPTIMOD-FM Card #PS, the
power supply re ulator card. If the values of R103 and R104 are already 0.62 ohms
(blue-red- old- old), or if “ pi yback ” resistors of 1.8 ohms (brown- ray-silver) have
been added in parallel to existin 0.91 -ohm resistors, skip to step d.
Card #PS is mounted on the inside of the rear panel. These lar e resistors can be seen
by openin the front panel, removin the subpanel, then lookin in the rear interior of
the unit to the left of Card #3. A flashli ht will be necessary.
b) Remove the OPTIMOD-FM from the rack, place it on a bench, and carefully open the
rear panel.
Set the unit on a pad with the rear panel facin you and about 6 ” (15cm) back from
the ed e of the bench. Make certain the power cord is unplu ed. Remove the screws
which attach the top and bottom covers to the rear panel (ei ht screws on each cover).
There is no need to remove the other cover screws. Remove the nine screws circled in
black on the rear panel. Very carefully and slowly pull the rear panel out about 3/4 ”
(2cm), then tilt the top ed e down until the rear panel is horizontal.
AUTION
Watch for sna s in the internal wirin and for any stress on
the ceramic capacitors on the divider wall or input filter box.
These capacitors are very fra ile and difficult to replace.
c) Connect a 1.8-ohm resistor in parallel with R103. Connect another 1.8-ohm resistor
in parallel with R104.
Two 1.8-ohm (brown- ray-silver-silver or brown- ray-silver- old), 1-watt wirewound
resistors are supplied with the XT2. Bend each lead at ri ht an les (about 1/8 ” from
the resistor bodies), then “ pi yback ” the new resistors onto the old on the component
side of the board. To avoid heat dama e, solder the leads to ether as far away from the
resistor bodies as practical. We su est you mark these chan es on the power supply
schematic. The net value of each resistor pair is now approximately 0.62 ohms.
d) If your OPTIMOD-FM is a Model 8100A (with a serial number below 638000),
skip to step 3.
If you have a Model 8100A/1 (serial number 638000 or above), close the rear panel
(but not the front panel) if open, remount the unit in the rack, skip the rest of the
RETROFIT INSTRUCTIONS, and follow the INSTALLATION INSTRUCTIONS on
pa e 2-3.
When replacin the rear panel, make sure that no wires are pinched under the flan es.

-8
Installation
3) Install accessory port in OPTIMOD-FM (Only in Model 8100A, S/N below
638000).
Allow about one hour for this step.
a) If a connector is installed in Accessory Port #1, remove the metal plate coverin
Accessory Port #2 and discard the plate and its fasteners.
If no connector is installed, remove the metal plate coverin both Accessory Ports.
Save the fasteners, and discard the plate. Install the metal plate from the Retrofit Kit
over Accessory Port #1, usin the fasteners from the discarded plate.
b) Install the connector in the rear-panel hole marked “ ACCESSORY PORT 2 ” with the
hardware provided (see Fi . 2-4). Note the orientation of the connector. Dress the
wires as shown, adjustin the cable ties as needed. Connect each wire to the mother,
board as indicated in the table in Fi . 2-4.
With only moderate force, use a #6 (3/16 ” ) hex nutdriver (a 5mm nutdriver will also
work) to ti hten the small screws.
The wire len ths have been chosen to provide enou h slack to enable other service
operations on the rear panel to be performed. It would be unwise to shorten the wires.
The routin shown should be followed to avoid possible crosstalk.
It is safe to tack-solder to the motherboard with the circuit cards in place except in very
hi h RF fields, in which case all cards should be removed. In any case, we recommend
usin a solderin iron with a rounded tip to minimize possibility of circuit dama e.
Avoid usin excessive amounts of heat or flux at the motherboard, since the connectors
could be dama ed by temperin of the contacts throu h excessive heat or by creepin
flux.
Because some of the motherboard traces are close to ether, inspect your work very
carefully to be sure that you have not created solder brid es between traces or pads.
c) Re-attach the rear panel by reversin the disassembly procedure.
When replacin the rear panel, make sure that no wires are pinched under the flan es.
4) Check, replace OPTIMOD-FM Card #5.
Allow about 5 minutes for this step.
In this and the followin two steps, you will be instructed to set cards aside rather than
reinstallin them. This is to save you from removin them a ain to set jumpers as directed
in the INSTALLATION INSTRUCTIONS.
AUTION
Be sure OPTIMOD-FM ’ s internal AC power switch is set to
OFF before removin or insertin any of the printed circuit
cards.

Installation -9
Fi . 2-4: Accessory Port #2 Installation
REAR
PANEL
iNSlDG
VIEW

-10
Installation
a) Remove Card #5 and check the part number etched on the solder side.
If the part number is 30741-000-03, the card you have is the correct one for use
with the XT2. Set the card aside (do not reinstall it yet) and skip to step 5. You may
return the Card #5 included with the Retrofit Kit to the factory for credit.
To do this, contact Orban Customer Service at one of the numbers at the front of this
manual to et a Return Authorization number. We will need to know the serial number
of your OPTIMOD-FM and the six-di it serial number stamped on the card itself. Only
the Card #5 included with the Retrofit Kit (not the one that was already in your unit)
will be accepted for credit. The duplicate Card #5 must be returned to us within 60 days
of the date of its shipment to you.
Upon receipt of your duplicate Card #5, we will mail a refund to the or anization
represented as the owner on the Re istration Card. If the Re istration card is not on
file, other proof of ownership will be required.
If the part number is 30451-000-nn (where -nn is any number) or 30741-000-02
■or -01, use the Card #5 provided in the Retrofit Kit (which will have an etched number
of 30741-000-03 or hi her) instead of the old card. Do not install the new card yet —
set it aside, takin care not to confuse it with the old card.
The old card is not returnable, but can serve as an emer ency spare (althou h you may
hear more processin artifacts with it).
5) Check, rework the OPTIMOD-FM Card #6.
Allow about one hour for this step.
The rework in this step enables the XT2 to defeat the OPTIMOD-FM ’ s hi h-frequency
limiters and soft clippers, and it redirects the output of Card #6 to the accessory port
installed in step 3.
a) Remove Card #6 check the part number etched on the solder side.
If the part number is 30461-000-05 or above, the card you have is the correct one
for use with the XT2. Set it aside and skip to step 6.
If the part number is 30461-000-04 or below, continue to step b.
b) Remove all the solder from both sides of the foil pad connected to the center terminal
of to le switch S602 with a vacuum desolderin tool. Use fairly stron dia onal
cutters to gently clip the center le of S602, leavin a stub on the switch lon enou h
to later solder two wires to (1/8 ” will do). Remove and discard the portion of tire le
formerly soldered to the card. Gentle wi lin with chain-nose pliers may help release
it.
c) Solder the banded (cathode) end of a lass 1N4148 diode to the pad where the center
le of S602 was attached.
d) Desolder the non-banded (anode) end of lass diode CR603 with a vacuum desolderin
tool. Bend the diode upward so that the free end is pointin toward S602. Usin the
lon wire from the kit, connect the free end of CR603 to the center terminal of S602.
Also connect the free end of the 1N4148 diode installed in step c to this terminal.
Carefully solder both diodes to the terminal. Avoid excess heatin and excess solder
or flux (which could creep into the switch).