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Section I

INTRODUCTION

MODEL 235 PRODUCT DESCRIPTION

Historical

Inovonics introduced its

Model 222 “NRSC” Processor

in 1987. This

product was developed to meet certain “AM improvement” needs and

became a very popular addition to existing audio processing systems in

broadcast markets of all sizes. The NRSC fixed pre-emphasis and low-

pass cutoff characteristics suggested in 1987 were subsequently

mandated by the U.S. Federal Communications Commission.

General

The 235 incorporates these same pre-emphasis and high-frequency-

cutoff characteristics to meet NRSC requirements, but its expanded

functions also include comprehensive program dynamics processing to

maximize perceived loudness and to fully utilize the modulation

capability of modern AM broadcast transmitters.
The 235 combines AGC, 3-band compression, low and high frequency

equalization, and tight control over program peaks with a combination

of hard limiting and judicious waveform clipping. Dynamics processing

is followed by an overshoot-compensated low-pass filter exceeding

NRSC specifications. The filter may be factory-tailored for other cutoff

frequencies to accommodate European medium-wave transmissions or

various international short-wave services.
Processing parameters are easily set with front-panel controls, or may

be controlled from a remote location using the built-in RS-232 control

bus and an IBM-compatible computer or modem interface.

Features

To recap, features of the Inovonics 235 include:

•

Comprehensive dynamic range processing which

combines:
—  Gated, “gain-riding” AGC
—  3-band average level compression
—  Low- and high-frequency program equalization
—  Asymmetrical peak limiting with selectable clipping

depth.

•

Low-pass filtering to the NRSC specification with

patented filter overshoot compensation. Alternative

cutoff frequencies can be provided.

•

Easy front-panel control of processing parameters, or

full computer control via RS-232 bus..

Содержание 235

Страница 1: ...OPERATING AND MAINTENANCE INSTRUCTION MANUAL MODEL 235 AM BROADCAST AUDIO PROCESSOR __________ ...

Страница 2: ...ate Purchased ___________ Warranty Card Mailed OPERATING AND MAINTENANCE INSTRUCTION MANUAL MODEL 235 AM BROADCAST AUDIO PROCESSOR March 1999 1305 Fair Avenue Santa Cruz CA 95060 TEL 831 458 0552 FAX 831 458 0554 Visit our Website www inovon com ...

Страница 3: ...nterference RFI 8 Location Ground Loops Line Input and Input Range Selection 8 Input Connection Balanced Input Unbalanced input Input Gain Range Gain Jumper Program Line Output 10 Output Connection and Signal Phase Rear Panel Mode Switch 10 Section III SETUP AND OPERATION Operational Overview and Panel Appointments 11 AGC Compression Program Density Equalization Peak Clip Limit Peak Processing Inp...

Страница 4: ...ntrol AGC Gating Triband Compressor 19 Fixed Pre Emphasis Band Pass Compression Compression Platform Variable Equalization 20 Peak Control 20 Filter Overshoot Compensation 21 Sources of Overshoot Phase Lag and Recombining Low Pass Filter 22 Output Stage 22 Gain Reduction Metering 23 Common Control Circuitry 23 Power Supply 24 Section VI APPENDIX Parts Lists 25 Explanation of Parts Listing Parts Li...

Страница 5: ...ht control over program peaks with a combination of hard limiting and judicious waveform clipping Dynamics processing is followed by an overshoot compensated low pass filter exceeding NRSC specifications The filter may be factory tailored for other cutoff frequencies to accommodate European medium wave transmissions or various international short wave services Processing parameters are easily set ...

Страница 6: ...hasis appropriate to the specified cutoff frequency Variable Equalization see Figures 2 and 3 on Page 5 HF 3dB 0dB NRSC 3dB 6dB 9dB variable EQ curves are in addition to the NRSC or alternative fixed pre emphasis LF 9dB 6dB 3dB 0dB flat 3dB Peak Controller Asymmetrical fast peak limiter integral with hard peak clipper PEAK PROCESSING controls release timing and program dependent clipping depth Low...

Страница 7: ...aracteristic Figure 2 LF Equalization Range dashed line represents subsonic high pass function Figure 3 HF Equalization Range 0dB represents NRSC fixed pre emphasis 9dB 6dB 3dB 0dB 3dB 3dB 0dB 3dB 6dB 9dB NRSC MODEL 235 RESPONSE ...

Страница 8: ...ck Diagram Model 235 AM Broadcast Audio Processor BALANCED LINE INPUT 50Hz LOW PASS INPUT GAIN G R AGC CONTROL AND GATING NRSC PRE EMPH G R HIGH PASS HIGH PASS HIGH FREQ EQ SELECT G R BAND PASS BAND PASS G R LOW PASS LOW PASS LOW FREQ EQ SELECT BALANCED LINE OUTPUT G R LOW PASS FILTER OVERSHOOT COMP OUTPUT LEVEL UART PIC FRONT PANEL CONTROLS INDICATORS RS 232 PORT BYPASS PROGRAM DENSITY PEAK PROCE...

Страница 9: ...IFICA TION INSTRUCTIONS should they be issued by Inovonics MOUNTING Rack Requirement The Model 235 mounts in a standard 19 inch equipment rack and requires only 1 inches 1U of vertical rack space Plastic finishing washers are recommended to protect the painted finish around the mounting holes Heat Dissipation Consuming less power than a counter top coffee grinder the 235 itself generates negligibl...

Страница 10: ...er our apologies cords come from many sources and advise that US color coding applies BLACK AC HOT WHITE AC NEUTRAL GREEN GROUND RADIO FREQUENCY INTERFERENCE R F I Location Although we have anticipated that the 235 will frequently be installed adjacent to high power AM transmitters please practice care and common sense in locating the unit away from abnormally high RF fields Ground Loops Because t...

Страница 11: ...on a jumper wire should be installed between the terminal and G Input Gain Range The Model 235 Processor can accommodate line level program input with a nominal Zero VU value between 15dBu and 15dBu This 30dB range is divided into two more manageable 15dB ranges with an internal jumper As shipped the 235 is jumpered for professional level inputs between 0dBu and 15dBu Most console and STL outputs ...

Страница 12: ...etry in the direction indicated that is the terminal will be additionally positive going with increased positive peaks Make sure that the terminal is connected to the transmitter input terminal which yields an increase in carrier level for a positive signal excursion REAR PANEL MODE SWITCH The 3 position toggle switch on the rear panel of the 235 selects OPERATE for local front panel operation REM...

Страница 13: ...d down for a number of reasons Among these are 1 an operator s lack of attention to manual gain riding 2 different interpretations of console level meter readings among board operators or 3 the misrepresentation of the program signal waveform by the traditional sluggish VU meter AGC in the 235 Processor is gated It does not hunt or bring up background noise during pauses in the program AGC gain fr...

Страница 14: ...is quite rapid release on the other hand is variable and a function of the PROGRAM DENSITY setting which is explained in more detail under the next heading The three COMPRESSION displays show dBs of gain reduction for each band PROGRAM DENSITY Two up down buttons allow the operator to choose eight relative degrees of density control These are indicated on the adjacent LED bar display Set at MIN th...

Страница 15: ... tolerate a good deal more clipping than solo vocals and voice announcements INPUT GAIN Input sensitivity of the Processor is adjusted by this 15 turn potentiometer to accommodate varying input levels The control itself has 15dB continuous adjustment This coupled with input level range jumpering Figure 5 Page 9 accommodates the 235 s full 30dB input signal level range The INPUT GAIN control is set...

Страница 16: ...hat both the 0dB AGC GAIN indicator and the one just below it 2 5dB light equally Remember that the AGC circuit responds very slowly to level change so exercise patience in making this important adjustment Once the INPUT GAIN has been adjusted with a test tone you can switch over to normal program material If the procedure has been performed properly and if the board operator pays reasonable atten...

Страница 17: ...cessor end or at the input of the transmitter but not both for heaven s sake to see if proper behavior is restored REMOTE CONTROL OF THE MODEL 235 Computer and Modem Compatibility Control software provided with the 235 is written in Visual Basic 5 It runs only under Windows 95 or subsequent 32 bit versions of Microsoft s popular operating system for IBM compatibles The software enables remote cont...

Страница 18: ... data output device and will have a DB09 or DB25 female connector A custom cable will need to be purchased or constructed Schematic Sheet 4 on Page 32 diagrams the several options for interconnect cables between the Model 235 and computer or modem ...

Страница 19: ...ssembly Main board components begin with the number 1 i e R1 C1 IC1 Front panel components are in the five hundred series i e R501 S501 The front panel assembly interconnects with the main board using three short ribbon cable jumpers J2 on the main board mates with J502 on the panel assembly J4 to J504 and J5 to J505 INPUT STAGE Schematic Sheet 1 Page 29 Line Input Balancing IC36B is an active bal...

Страница 20: ...ion If this circuit is unfamiliar to you don t feel bad It is somewhat unconventional and dates from one of Inovonics first products developed in the early 1970s It is also the subject of a patent long since expired Rectifier and AGC Control IC39B and IC40B along with diodes CR27 and CR28 give full wave peak rectification of the gain controlled input signal R197 and C67 yield the 10 millisecond in...

Страница 21: ...29 Fixed Pre Emphasis C53 is in the input path of IC38A imparts the fixed NRSC pre emphasis to the program signal ahead of the 3 band compressor The resultant increase in high frequency energy is kept in check by normal compressor action Band Pass Compression IC28B is a first order band pass stage defining a second order response for the MID band Gain control ahead of this stage gives a distortion...

Страница 22: ...ts of the three compressor sections are combined in summing stage IC34A The MID band is fed through fixed resistance R127 but the LOW and HIGH bands are routed through selectable networks IC33 and IC37 allow selection of five EQUALIZATON settings both for LOW FREQ and HIGH FREQ This varies the gain of the LOW and HIGH bands in the final output mix Equalizer curves are shown on Page 5 PEAK CONTROL ...

Страница 23: ...hoot control permit the primary low pass filter to overshoot then isolate and re introduce the overshoots to cancel themselves in the signal path The patented overshoot compensator in the 235 on the other hand pre conditions the limited program signal ahead of the filter so there is little or no tendency for the filter to generate overshoots in the first place Phase Lag and Recombining As previous...

Страница 24: ... of how the FDNR circuit works than we could possibly deliver here due not only to the limited scope of this Instruction Manual but to our own marginal understanding of how these confounded things work IC22A buffers the output of the low pass filter and IC21A provides phase inversion and gain to compensate for filter insertion loss The signal level corresponding to 100 symmetrical modulation at th...

Страница 25: ...ontrol voltages from I3B Thus a common log converter and display driver can serve the four multiplexed gain reduction displays COMMON CONTROL CIRCUITRY Schematic Sheet 3 Page 31 The 235 makes efficient use of a device called a PIC or Peripheral Interface Controller IC8 on the Schematic This is a simple single chip microcontroller meant for elementary logic and uncomplicated control functions We pr...

Страница 26: ... PIC POWER SUPPLY Schematic Sheet 2 Page 30 Model 235 circuitry utilizes 9 volt supplies for op amps and other linear circuitry and a 5 volt supply for digital logic These three sources are each regulated by a 3 terminal linear voltage regulator IC4 for 9 volts IC6 for 9 volts and IC5 for 5 volts The power transformer T1 has dual primary windings which may be switched in parallel or in series to a...

Страница 27: ... 25 Section VI APPENDIX The following section of this Manual contains Parts Lists and Schematic Diagrams for the Model 235 and an explanation of Inovonics Warranty Policy ...

Страница 28: ...ecified as follows a 100pF to 0 47µF are of the metalized mylar or polyester variety Whole number P values are picofarads decimal values are microfarads 5 50VDC or better The style used in the 540 is the minibox package with a lead spacing of 0 2 inch Preferred part Wima MKS 2 or FKC 2 series Alternates CSF Thompson IRD series or Roederstein KT 1808 or KT 1817 series b 1 0µF and above are radial l...

Страница 29: ...tegrated Cct Maxim MAX232 IC8 Integrated Cct SPECIAL FACTORY PROGRAMMED PIC type 16C62A Order by designation reference Model 235 IC9 Integrated Cct open mfgr 74HC148 IC10 11 15 16 Integrated Cct open mfgr 74HC138 IC14 33 37 43 Integrated Cct open mfgr CMOS 4051B IC27 42 Integrated Cct open mfgr CMOS 4053B IC501 Integrated Cct open mfgr LM3914N J1 AC Mains Connector PC mounting Switchcraft EAC303 J...

Страница 30: ...liers of small quantities of replacement parts for professional equipment The temptation to use cross referenced hobbyist or TV shop direct replacement parts ha should be avoided Any semiconductor IC capacitor resistor or connector used in the Model 235 is probably available from one or more of these firms Each supplier publishes a full line catalog available free for the asking Minimum order rest...

Страница 31: ... 29 Schematic Sheet 1 29 ...

Страница 32: ... 30 Schematic Sheet 2 30 ...

Страница 33: ... 31 Schematic Sheet 3 31 ...

Страница 34: ... 23 10 22 9 21 8 20 7 19 6 18 5 17 4 16 3 15 2 14 1 COMPUTER DB25 Female 5 9 4 8 3 7 2 6 1 MODEL 235 DB9 Male MODEM DB25 Male 13 25 12 24 11 23 10 22 9 21 8 20 7 19 6 18 5 17 4 16 3 15 2 14 1 5 9 4 8 3 7 2 6 1 MODEL 235 DB9 Male 5 9 4 8 3 7 2 6 1 COMPUTER DB9 Female 5 9 4 8 3 7 2 6 1 MODEL 235 DB9 Male 5 9 4 8 3 7 2 6 1 MODEM DB9 Male ...

Страница 35: ...ved or altered III TERMS OF WARRANTY Inovonics Inc products are warranted to be free from defects in materials and workmanship A Any discrepancies noted within 90 days of the date of delivery will be repaired free of charge or the equipment will be replaced with a new or remanufactured product at Inovonics option B Additionally parts for repairs required between 90 days and one year from the date ...

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