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Inovonics 235 Operating And Maintenance Instruction Manual

Am broadcast audio processor
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OPERATING AND MAINTENANCE
INSTRUCTION MANUAL
MODEL 235
AM BROADCAST AUDIO PROCESSOR
__________

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Summary of Contents for Inovonics 235

  • Page 1 OPERATING AND MAINTENANCE INSTRUCTION MANUAL MODEL 235 AM BROADCAST AUDIO PROCESSOR __________...
  • Page 2 —– USER’S RECORD —– Model 235 - Serial No. ______ Date 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...

  • Page 3: Table Of Contents

    TABLE OF CONTENTS Section I - INTRODUCTION Model 235 Product Description ................... Historical - General - Features Model 235 Technical Specifications..................Block Diagram ........................Section II - INSTALLATION Unpacking and Inspection ....................Mounting ..........................Rack Requirements - Heat Dissipation AC (Mains) Power........................
  • Page 4 Remote Control of the Model 235 ..................Computer and Modem Compatibility - Interconnection - Section IV - CIRCUIT DESCRIPTIONS Navigation ........................... Input Stage .......................... Line Input Balancing - High-Pass Subsonic Filter AGC Amplifier ........................Antediluvian Gain-Control Element Explained - Rectifier and AGC Control - AGC Gating Triband Compressor ......................

  • Page 5: Section I - Introduction

    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.

  • Page 6: Model 235 Technical Specifications

    MODEL 235 TECHNICAL SPECIFICATIONS Frequency Response (NRSC version): Peak Controller: PROOF: ±0.25dB, 50Hz to 20kHz Asymmetrical fast peak limiter OPERATE: ±0.5dB, 50Hz to 9.7kHz. integral with hard peak clipper. PEAK Follows NRSC pre-emphasis and PROCESSING controls release timing cutoff characteristics.
  • Page 7 MODEL 235 Figure 1 - NRSC Cutoff RESPONSE Characteristic –9dB –6dB –3dB +3dB Figure 2 - LF Equalization Range (dashed line represents subsonic high-pass function) –3dB +3dB +6dB +9dB (NRSC) Figure 3 - HF Equalization Range (“0dB” represents NRSC fixed pre-emphasis) —...

  • Page 8: Block Diagram

    BLOCK DIAGRAM A simplified Block Diagram of the Model 235 is shown in Figure 4, below. Processor circuitry is detailed in the Circuit Descriptions section beginning on Page 17. These descriptions reference Schematic Diagrams found in the Appendix. INPUT GAIN...

  • Page 9: Section Ii - Installation

    AC (MAINS) POWER Unless specifically ordered for export shipment, the Model 235 is set at As delivered the factory for operation from 115V, 50/60Hz AC mains. The rear- panel designation next to the fuseholder will confirm both the mains voltage selected and the value of a proper fuse.

  • Page 10: Radio Frequency Interference (Rfi)

    Please note that the screw-terminal barrier block can be unplugged from the chassis, simply by pulling it straight out! This makes connection a bit easier and allows quick removal of the 235 — —...
  • Page 11 This makes connection a bit easier and allows quick removal of the 235 from the rack should maintenance ever be required. A balanced program audio feed to the 235 Processor will use both the Balanced Input + and the – terminals, plus the associated G (ground). Since this is a bridging (high impedance) input, it does not provide a ‘termination’...

  • Page 12: Program Line Output

    Processor and transmitter will partially (or completely!) negate the tight final peak control which the 235 provides. This means that the 235 must be located at the transmitter site to be completely effective. Even a digital link (STL, ISDN, FRAC-T1 or FDIC) will compromise the peak control function.

  • Page 13: Section Iii - Setup And Operation

    SETUP AND OPERATION OPERATIONAL OVERVIEW AND PANEL APPOINTMENTS This section leads off with an overview of the 235 Processor with particular reference to front-panel indicators and controls. All functions are described and explained in this overview. Whether or not you believe in reading Manuals, please at least check these descriptions to verify that our terminology is in agreement with your understanding.
  • Page 14 EQUALIZATION In addition to NRSC (or alternative) fixed pre-emphasis, the 235 provides a range of control over both high- and low- frequency program equalization. The effect of the equalizers is shown in Figures 2 and 3 on Page 5.
  • Page 15 EQUALIZATION settings through the five choices for each end of the spectrum. The final processing block of the 235 is a unique CLIP asymmetrical “feedback” peak-limiter/clipper. A final PEAK clipping circuit is able to monitor its own action and tell the...

  • Page 16: Processor Setup Procedure

    PROCESSOR SETUP PROCEDURE This setup procedure assumes a typical, transmitter-site installation of the 235, with the LINE INPUT fed from the output of the console or from a telephone line or STL receiver. At this point the Processor should be installed in the program chain with power applied.

  • Page 17: Possible Problems

    Processor 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 ® Control software provided with the 235 is written in Visual Basic 5 . It Computer and ®...
  • Page 18 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. — —...

  • Page 19: Section Iv - Circuit Descriptions

    Audio Processor. Circuit descriptions refer to four pages of Schematic Diagrams contained in the Appendix, Section V, Pages 29 through 32. If you’re looking for some sort of alignment procedure for the 235, forget it. There are no internal controls for any sort of calibration, the circuitry being rock-solid through impeccable design.

  • Page 20: Agc Amplifier

    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.

  • Page 21: Triband Compressor

    correction. The time constant of R173 and C58 determine the slow, unobtrusive, 0.5dB/second correction rate of the AGC. The level-corrected program signal is monitored by the gating AGC Gating amplifier, IC38A. This is a first-order, band-pass filter with –3dB points at 300Hz and 3kHz. The purpose of this frequency weighting is to favor legitimate program material, and neglect rumbles and hisses which might otherwise cause the AGC to bring these noises to annoying levels.

  • Page 22: Compression "Platform

    that described for the MID band, except that time constants are scaled appropriately. At the (MIN) PROGRAM DENSITY setting, IC43 selects R208 as a Compression discharge path for C59. The DC control voltages from all three bands “Platform” combine to charge C59 to an average of the three. This establishes a compression “platform,”...

  • Page 23: Filter Overshoot Compensation

    Even a fully phase-corrected filter will exhibit overshoots, and a 9-pole “elliptic” filter, like the one used in the Model 235 Processor, can overshoot 3dB or more... perhaps much more!

  • Page 24: Low-Pass Filter

    L-C design worked-out in Germany during the late 1940s, probably with a slide rule! The particular active configuration used in the 235 is sometimes called the “FDNR” because each of the legs to ground simulates a Frequency-Dependent Negative Resistance.

  • Page 25: Gain Reduction Metering

    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.

  • Page 26: Power Supply

    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;...

  • Page 27: Section Vi - Appendix

    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. — —...

  • Page 28: Parts List

    PARTS LIST EXPLANATION OF PARTS LISTINGS This section contains listings of component parts used in the Inovonics 235 AM Broadcast Audio Processor. These are listed either en-masse, or by schematic component reference designation. The listing may, or may not, specify a particular manufacturer. When no manufacturer is called-out, the term “open mfgr.”...
  • Page 29 Integrated Cct.; (open mfgr.) LM337-T (Uses Aavid 574602 B03700 Heat Fin) Integrated Cct.; Maxim MAX232 Integrated Cct.; SPECIAL FACTORY-PROGRAMMED “PIC,” type 16C62A. Order by designation, reference Model 235. Integrated Cct.; (open mfgr.) 74HC148 IC10,11,15,16 Integrated Cct.; (open mfgr.) 74HC138 IC14,33,37,43 Integrated Cct;...

  • Page 30: Mail-Order Component Suppliers

    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 restrictions may apply; and export orders may be difficult.

  • Page 31: Schematics

    Schematic Sheet 1 — 29 — — —...
  • Page 32 Schematic Sheet 2 — 30 — — —...
  • Page 33 Schematic Sheet 3 — 31 — — —...
  • Page 34 MODEL 235 DB25 Male DB9 Male DB25 Female DB9 Male MODEM MODEL 235 COMPUTER MODEL 235 DB9 Male DB9 Male DB9 Female DB9 Male Interconnect Cables — Model 235 Processor to Computer or Modem Schematic Sheet 4 — 32 —...
  • Page 35 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’...

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