Orban RET-044 Manuel du propriétaire

orbon*

Installation and Operation Instructions

RETROFIT KIT RET-044

For OPTIMOD-AM Models 9000A and 9000A/1

Purpose: Adds NRSC Pre-emphasis and 10kHz Low-pass Filter

This kit modifies the Model 9000A or 9000A/1 OPTIMOD-AM® to provide the pre-

emphasis and 10kHz low-pass filtering that is required by the National Radio Systems

Committee (NRSC). 11kHz and 5kHz low-pass filtering are provided for stations that re-

quire them. The filters can be preset, or can be switched by OPTIMOD-AM’s day/night

logic. This kit also provides ameans of de-emphasizing the NRSC pre-emphasized

signal for monitoring.

Retrofit Kit RET-044 contains;

Capacitor, 1300pF ±2%, mica

Resistor, 5.49K ±1%, Vs-watt, metal film

Resistors, 8.66K ±1%, Va-watt metal film

Resistor, 3.1 6K ±1%, Va-watt metal film

Resistor, 49.9K ±1%, Va-watt metal film

Resistor, 1.27meg ±1%, Va-watt metal film

(green-yellow-white-brown-brown)

(gray-blue-blue-brown-brown)

(orange-brown-blue-brown-brown)

(yellow-white-white-red-brown)

(brown-red-violet-yellow-brown)

Resistor, 10.0K±1%, Va-watt metal film (brown-black-black-red-brown)

Opamp (TL072) 1C

Capacitor, 0.1 |xF ±10% metallized polyester

28-gauge jumper wire

Resistor, 75.0K±1%, Va-watt metal film (violet-green-black-red-brown)

Pre-wired 22-pin card connector with mounting hardware

Card guides

#1 F10 Card

Label, “Special Modification"

Resistor, lOOn ±5%, 'A-watt, carbon film

Resistors, 620J2 ±5%, V4-watt, carbon film

Capacitor, 0.18)xF ±5%, 100-volt, metallized polyester

Installation and Operation Instructions

These instructions first discuss the reasons behind the NRSC requirements (starting on

the following page), then explain how to install the retrofit (on page 3).

Installation consists of replacing components on Cards #3 and #8, installing anew

card edge connector, setting jumpers, and plugging in anew circuit card. Asimple

de-emphasis circuit can be installed for off-air monitoring.

New operation information and technical notes follow the installation instructions. Also

included are field alignment and performance verification instructions, acircuit de-

scription, aparts list, aschematic, and an assembiy drawing for Card #1F10.

P/N 95302-000-04

lOO-FB-6/92 Orban, adivision of AKG Acoustics, Inc.

1525 Alvarado Street, San Leandro, California 94577 USA

Phone: (510) 351-3500 FAX: (510) 351-0500

page 2RET-044 Instructions

Why the New NRSC Standard?

Over the years, as the North American air waves has become more crowded, interference

from first and second adjacent stations has become more and more of aproblem. Receiver

manufacturers responded by producing receivers with decreased audio bandwidth, so that an

adjacent station’s modulation extremes would not be audible as interference. This cutting

of the bandwidth had the effect of reducing the receiver’s high-frequency response, but it

was felt that lower fidelity would be less obnoxious than interference. As long ago as 1978,

Orban proposed and implemented pre-emphasis and low-pass filtering for AM broadcast to

provide brighter sound at the receiver while minimizing interference. This approach has

become widely accepted. Now the NRSC has formalized astandard which is acceptable to

all industry segments, and which can, if promptly implemented, result in avast improvement

in AM radio.

AM Stereo Introduces aPre-emphasis Dilemma

Certain AM receivers manufactured since 1984 for sale in North America, particularly those

designed for domestic AM stereo reception, have afrequency response that is substantially

wider than that of the typical mono AM receiver. The frequency response was widened largely

to enhance the sales potential of AM stereo by presenting adramatic, audible improvement

in fidelity in the showroom. As these new receivers became more prevalent, broadcasters

had to choose whether the station’s pre-emphasis would be optimized for the new AM stereo

receivers or for the existing conventional receivers that form the vast majority of the market. If

the choice was for conventional receivers (which implies arelatively extreme pre-emphasis),

the newer receivers might sound strident or exceptionally bright. If the choice favored the

newer receivers (less pre-emphasis and probably less processing), the majority of receivers

would be deprived of much high-end energy and would sound both quieter and duller.

NRSC Standard Pre-emphasis and Low-pass Filtering

In response to this dilemma, the National Radio Systems Committee (NRSC) undertook the

difficult task of defining avoluntary recommended pre-emphasis curve for AM radio that

would be acceptable to broadcasters (who want the highest quality sound on the majority

of their listeners’ radios) and to receiver manufacturers (who are primarily concerned with

interference from first- and second-adjacent stations).

After ayear of deliberation, a‘modified 75-microsecond’ pre-emphasis/de-emphasis standard

was approved. This provides amoderate amount of improvement for existing narrowband

radios, while optimizing the sound of wideband radios. Most importantly, it generates sub-

stantially less first-adjacent interference than do steeper pre-emphasis curves. The second part

of the NRSC standard calls for asharp upper limit of lOkHz for the audio presented to the

transmitter. This essentially eliminates interference to second and higher adjacencies. While

some have protested that this is inadequate and that 15kHz audio should be permitted, the

unfortunate fact is that interference-free 15kHz audio could only be achieved by acomplete

re-allocation of the AM band! The practical effect of widespread implementation of the

lOkHz standard is that lOkHz radios will then be feasible, and the bandwidth perceived by

the average consumer (now limited by the receiver to 3kHz, typically) will be dramatically

improved. On much mass-market consumer equipment, it will be difficult to tell AM from

FM.

RET-044 Instructions page 3

On April 27, 1989, The FCC (U.S.A.) released aReport and Order that amended section

73.44 of the FCC Rules by requiring all U.S. AM stations to comply with the occupied

bandwidth specifications of the NRSC-2 standard by June 30, 1990. The NRSC-2 standard is

an ‘RF mask’ that was derived from the NRSC-1 audio standard by the NRSC. The purpose

of the NRSC-2 RF mask is to provide atransmitted RF occupied bandwidth standard that any

station with aproperly-operating transmitter will meet, provided thatNRSC-1 audio processing

is used prior to the transmitter, and provided that the station is not over-modulating.

The Report and Order provides for ‘presumptive compliance’ with the NRSC-2 occupied

bandwidth standard: Prior to June 30, 1994, any station whose audio complies with the

NRSC-1 standard (an audio standard) is presumed to comply with the NRSC-2 standard (an

RF occupied bandwidth standard), unless the station receives an Official Notice of Violation

or aNotice of Apparent Liability from the Commission alleging non-compliance with the

NRSC-2 occupied bandwidth standard.

Orban welcomes the FCC’s decision: The radio manufacturers participating in the NRSC

stated emphatically that reduction in interference must be demonstrated by broadcasters be-

fore receiver manufacturers would be willing to release true wideband (lOkHz audio band-

width) receivers to the mass market. This is rational —the receiver manufacturers can lose

millions of dollars if they produce receivers that are rejected as noisy or interference-prone

by consumers. In contrast, broadcasters can easily change pre-emphasis and filtering with

very little expense.

It would therefore be wise to strictly conform to the standard even if it were not required by the

FCC. We are convinced that use of this more modest pre-emphasis and sharp lOkHz filtering

by broadcasters is the only factor that will eventually induce the receiver manufacturers to

build and mass-market the high-fidelity, wideband radios which would allow AM stations to

compete with FM in audio quality. The commitment to do so was strongly expressed by the

receiver manufacturers involved in the NRSC’s deliberations.

Installation

In these instructions “OPTIMOD-AM” refers to either of Models 9000A or 9000A/1. For

the purposes of this retrofit, your unit should be considered to be a“9000A/1” if there are

DAY and NIGHT indicators and axmtr eq switch on the right side of the subpanel; if these

are not present, you have a“9000A.” (Use the presence or absence of the XMTR EQ switch

and LEDs to determine your model number for this retrofit —some units labeled “9000A”

have been upgraded to 9000A/1 units.)

You will need aset of tools suitable for printed circuit board repairs. Refer to the drawings

in your OPTIMOD-AM Operating Manual for location of parts. All parts needed for this

retrofit are supplied in this kit.

Allow about 2hours for this retrofit.

CAUTION: The reliability of your unit can be compromised by poor workmanship. Refer to

“Replacement of Components on Printed Circuit Cards’’ in Section 4of your OPTIMOD-AM

Operating Manual (page 4-4 in the 9000A Manual, page 4-13 in the 9000A/1 Manual) for

instructions on how to rework the cards without damaging them or making them unreliable.

page 4RET-044 Instructions

1) Open the front panel of OPTIMOD-AM, remove the subpanel.

a) Disconnect OPTIMOD-AM, remove it from the rack, and place it on awork bench.

b) Remove the three screws at the top of the front panel, then tilt the hinged front panel

downward to reveal the interior.

c) Set the AC power switch to OFF.

d) Loosen the four DZUS fasteners on the subpanel by turning each 'A-tum counterclock-

wise with along Vi6-inch or 'A-inch flat-blade screwdriver.

e) Taking 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 right.

NOTE: Due to mechanical interference. Cards #3 and #5 must be removed before

Cards #4 and #6 can be removed. (There is, however, no need to remove Card

#4 or #6 for this retrofit.)

2) Remove and replace components on Card #3.

a) Remove Card #3 from its slot.

b) Remove and replace the following components on Card #3.

This step modifies OPTIMOD-AM’s “input conditioning filter” on Card #3 to

obtain “modified 75gs” pre-emphasis.

Remove: Replace with the supplied:

C305 (4700pF capacitor)

C307 (160pF mica capacitor)

R309 (35.7K resistor)

R310 (28.0K resistor)

R311 (28.0K resistor)

R312 (4.53K resistor)

—(discard C305) —

1300pF ±2% mica capacitor

5.49K resistor (green-yellow-white-brown-brown)

8.66K resistor (gray-blue-blue-brown-brown)

3. 16K resistor (orange-brown-blue-brown-brown)

c) Remove and replace the following components on Card #3.

This step retunes the high-pass filter within the “input conditioning filter” from

lOOHz to 50Hz. These changes are not required by the NRSC standard, but

are strongly recommended by Orban to improve the audible bass quality of the

processing.

Remove:

R304 (24.9K resistor)

R305 (634K resistor)

R306 (4.99K resistor)

1C302 (RC4558)

Replace with the supplied:

49.9K resistor (yellow-white-white-red-brown)

1.27meg resistor (brown-red-violet-yellow-brown)

lO.OK resistor (brown-black-black-red-brown)

TL072

Be sure that the IC chip is correctly oriented in its socket, with the notch or dot

on the chip on the same side as the “tab” on the circuit board foil pattern.

d) Cormect the supplied O.lpF polyester film capacitor in parallel with resistor R345 on

Card #3.

This step makes the operation of the Broadband Compressor smoother by de-

emphasizing its control sample (so that it sees a“flat” signal and does not produce

unnatural gain reduction on program material rich in high frequencies). This

modification is not required by the NRSC standard, but is recommended by Orban.

e) Return Card #3 to its slot.

RET-044 Instructions page 5

3) Cut jumper, install Jumper and resistor on Card #8 {with xmtr eq switch).

[Skip this step unless your OPTIMOD-AM has DAY and NIGHT indicators and a XMTR EQ

switch on the right side of the subpanel and your Card #8 is Assembly Number 30381-000-

02.]

There are three versions of Card #8: one with transmitter equalization, one with-

out, and one with Assembly Number 30381-000-02 (The assembly number is

located on the solder side of the card).

a) Remove Card #8 from its slot.

b) Verify that jumper 2on Card #8 is in the “DAY ONLY” position (unless you have a

NIGHT filter installed on Card #8, and you want to continue using it at night).

See Fig. 1for jumper location.

c) Cut and remove the jumper labeled “3” on the Card #8 assembly drawing in the

9000A/1 Operating Manual.

This jumper is located very close to finger 20 on the card’s edge.

d) On the solder side of the card, solder one end of the supplied jumper wire to pin 7of

IC804’s socket (-2.0VDC clipper bias source).

e) Solder the other end of that wire to finger Lof the card edge connector.

Finger Lis the tenth pin down from the top, counting finger Aas the first finger.

Note that G, I, O, and Qare skipped in the labeling sequence.

Use only atiny amount of solder, and solder to the very inner edge of the finger

to avoid contaminating the gold mating surface of the finger with solder. Clean

away any flux residue with solvent.

f) Solder the supplied 75.OK (vioiet-green-biack-red-brown) resistor between pins 1and 3of

R817, the large OUTPUT ATTENuator control.

Fig. 1;Jumper Position, Card #8 (with transmitter equalization)

page 6RET-044 Instructions

4) Cut jumper and install resistor on Card #8 {without xmtr switch).

[Skip this step ifyour OPTIMOD-AM has DAY and NIGHT indicators and aXMTR EQ switch

on the right side of the subpanel, or ifyour Card #8 is Assembly Number 30381-000-02.]

There are three different versions of Card #8: one with transmitter equalization,

one without, and one with Assembly Number 30381-000-02 (The assembly num-

ber is located on the solder side of the card).

a) Remove Card #8 from its slot.

b) Cut and remove the jumper labeled “STEREO OPTION JUMPER” on the Card #8

assembly drawing in the 9000A Operating Manual.

This Jumper is located very close to pin 20 on the card edge connector.

c) Solder the supplied 75.OK (violet-green-black-red-brown) resistor between pins 1and 3of

R817, the large OUTPUT ATTENuator control.

d) Return Card #8 to its slot.

5) Cut trace, and install resistor on Card #8 {with Assembly Number30381-000-02).

[Skip this step ifyour Card #8 is not Assembly Number 30381-000-02.]

There are three versions of Card #8: one with hansmitter equalization, one with-

out, and one with Assembly Number 30381-000-02 (The assembly number is

located on the solder side of the card).

a) Remove Card #8 from its slot.

b) Cut the trace between point 2and the adjacent trim pot.

c) Connect point 2to edge connector pin 20.

d) Connect the trim pot terminal disconnected in step 1to edge connector pin 19.

e) Return Card #8 to its slot.

6) Install edge connector and card guides for slot #1.

a) Remove the 30 screws that attach the top cover to the chassis, then lift off the top

cover.

b) Remove the eight screws that attach the bottom cover to the rear panel.

c) Set the unit on apadded surface with the rear panel facing you and the bottom cover

down.

Leave about 6inches (15cm) between the rear panel and the edge of the table.

Be sure the AC power cord is unplugged.

d) Remove the nine screws in three vertical groups on the rear panel.

One group of three is located at the left edge of the rear panel, one on the right

edge. The third group is located about one-third of the way from the right edge.

RET-044 Instructions page 7

e) Very carefully pull the rear panel about %-inch (2cm) toward you, and then tilt the top

of the rear panel down until the rear panel is horizontal.

Careful! Watch for snags in the wiring or stress on the ceramic capacitors on the

internal divider wall or RF box. These capacitors are very fragile and are difficult

to replace.

f) Attach the supplied edge connector to the circuit card cage at the rear of what will be

slot #1 (to the left of Card #2) with the supplied screws and nuts.

Use the other edge connectors as models for installation.

g) Working from the front of the unit, pop the two plastic card edge guides into their

supports at the top and bottom of the card cage.

Again, use the existing guides as models.

h) Ifyou have aOPTIMOD-AM with transmitter equalization, connect the wires from the

edge connector you just installed to the other edge connectors as follows.

[Skip to step iunless your OPTIMOD-AM has DAY and NIGHT indicators and a

XMTR EQ switch on the right side ofthe subpanel.]

The 9000A/1 employs wire-wrap connections. To connect awire, wrap it over

and solder it near the end of the indicated wire-wrap pin.

The pins may be numbered on the connector body. If not, count down from the

top. Alphabetic pins are those in the left row (the side furthest from the power

supply). When counting alphabetic pins, skip G, I, O, and Q. To avoid errors,

first mark the tip of every pin to be connected with afelt tip pen, then check the

marks again before beginning work.

Connect wire from: To: Function:

slot #1, pin Ascrew at top of slot #2 chassis ground

slot #1, pin Bslot #2, pin 2+15VDC

slot #1, pin Cslot #2, pin 3circuit ground

slot #1, pin Eslot #2, pin 5-15VDC

slot #1, pin Tslot #8, pin JNIGHT logic

slot #1, pin Uslot #8, pin L-2.0VDC clipper bias

slot #1, pin Vslot #8, pin 7-t-2.0VDC clipper bias

slot #1, pin Xslot #8, pin 19 Card #1F10 audio output

slot #1, pin Yslot #8, pin 20 Card #1F10 audio input

page 8RET-044 Instructions

i) Ifyou have aOPTIMOD-AM without transmitter equalization, connect the wires from

the edge connector you just installed to the other edge connectors as follows.

[Skip to step jifyour OPTIMOD-AM has DAY and NIGHT indicators and aXMTR

EQ switch on the right side of the subpanel.]

The 9000A employs wire-wrap connections. To connect awire, wrap it over and

solder it near the end of the indicated wire-wrap pin.

The pins may be numbered on the connector body. If not, count down from the

top. Alphabetic pins are those in the left row (the side furthest from the power

supply). When counting alphabetic pins, skip G, I, O, and Q. To avoid errors,

first mark the tip of every pin to be connected with afelt tip pen, then check the

marks again before beginning work.

Connect wire from: To: Function:

slot #1, pin Ascrew at top of slot #2 chassis ground

slot #1, pin Bslot #2, pin 2+15VDC

slot #1, pin Cslot #2, pin 3circuit ground

slot #1, pin Eslot #2, pin 5-15VDC

slot #1, pin Tslot #8, pin 3circuit ground

slot #1, pin Uslot #8, pin 6-2.0VDC clipper bias

slot #1, pin Vslot #8, pin 7+2.0VDC clipper bias

slot #1, pin Xslot #8, pin 19 Card #1F10 audio output

slot #1, pin Yslot #8, pin 20 Card #1F10 audio input

Check all your work very carefully by retracing all steps. Look for solder bridges.

k) Very carefully tilt the rear panel up to the vertical position, and the push the rear panel

forward into place.

Take care that no wires are pinched between the panel and the chassis.

l) Replace the 9rear-panel screws removed above.

Do not tighten screws until all screws are loosely in place, and the flanges of the

rear panel are aligned with those of the side panels.

m) Replace the top cover and the 30 screws that hold it in place.

Replace all screws loosely before tightening them. For best RFI protection, replace

and firmly tighten all screws.

n) Replace the eight screws that attach the bottom cover to the rear panel.

RET-044 Instructions page 9

7) Install Card #1F10.

NOTE: The “12kHz” positions of Card #1F10 in fact bypass all filters on the card.

Since the nominal bandwidth of the 9000A or 9000A/1 is llkHz without further

filtering, read “llkHz” whenever you see “12kHz” in the following text.

Card #1F10 contains the sharp lOkHz low-pass filter necessary to restrict the output

spectrum of the processor within NRSC standards. It also contains a5kHz 30dB/octave

low-pass filter (for international use). When jumpers Aand Bare in the “12kHz” position,

the 5kHz and lOkHz filters are bypassed (and OPTIMOD-AM’s built-in llkHz band

limiting remains in effect). In the 9000A/1 (but not in the 9000A), Card #1F10 follows

the DAY/NIGHT logic on Card #8.

a) Position jumper A(day) on Card #1F10 to select the low-pass filter (see Fig. 2).

You may select 5kHz, lOkHz, or 12kHz low-pass filtering in any combination for

day and night operation. The NRSC standard specifies lOkHz low-pass filtering

for both day and night.

IMPORTANT: The 9000A is always in the DAY mode. Select low-pass filtering

with jumper A(jumper Bhas no effect).

b) Insert Card #1F10 into slot #1.

#1F10 OO 5kHz —-OO

lo oH—10kHz —

|o o| NRSC (as shipped)

oo-—12kHz —o o

JUMPERS JUMPER A

NIGHT DAY

(inactive on 9000A)

Fig. 2: Low-pass Filter Jumper Positions. Card #1F10

page 10 RET-044 Instructions

8) Replace subpanel and close the front panel.

The subpanel should always be replaced, since it is an integral part of the chassis RFI pro-

tection.

a) Taking 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 at the right.

b) Turn the DZUS fasteners ’/4-tum clockwise.

The DZUS fasteners turn only 'A-tum. Don’t force them, lest they be damaged

in away that is very time consuming to repair.

c) Set the internal AC power switch to ON.

d) Raise the front panel and fasten the three screws that secure it in place.

e) Return OPTIMOD-AM to its rack, connect and ground unit.

9) Attach the supplied “Special Modification” label to the rear panel.

10)

Install NRSC de-emphasis circuit.

Asimple de-emphasis circuit can be placed between the audio output of the modula-

tion monitor and the input of the monitor amplifier to provide complementary 75ps de-

emphasis. For amore precise simulation of a“standard” NRSC receiver (including a

lOkHz notch filter to reduce any audible artifacts that might result from ringing introduced

by the very sharp lOkHz low-pass filter, and to eliminate lOkHz whistles encountered in

off-air monitoring), we recommend our ACC-023 NRSC Monitor Rolloff Filter.

See Fig. 3for aschematic of the simplified rolloff filter and information about installing

it (the parts needed are included in this kit). Note that the frequency response of this filter

is correct only when both its source and load impedances are 600 ohms, and that resistors

or pads may have to added to achieve this.

Modulation Monitor Monitor Rolloff Filter Monitor Amp or D.A.

Fig. 3: NRSC Simplified 75ps Monitor Rolloff Filter Schematic

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