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Related Manuals for Inovonics DAVID-II 716
Summary of Contents for Inovonics DAVID-II 716
- Page 1 OPERATING AND MAINTENANCE INSTRUCTION MANUAL “DAVID-II” ——— MODEL 716 ——— FM-STEREO PROCESSOR / GENERATOR __________ interstage Phistersvej 31, 2900 Hellerup, Danmark Telefon 3946 0000, fax 3946 0040 www.interstage.dk - pro audio with a smile...
- Page 2 —– USER’S RECORD —– Model 716 - Serial No. _______ Date Purchased _____________ Warranty Card Mailed — ¨ OPERATING AND MAINTENANCE INSTRUCTION MANUAL DAVID-II —–—— MODEL 716 ———– FM-STEREO PROCESSOR / GENERATOR October, 1995 1305 Fair Avenue, Santa Cruz, CA 95060 TEL: (408) 458-0552 –...
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Page 3: Table Of Contents
TABLE OF CONTENTS Section I - INTRODUCTION Model 716 Product Description ................... General - Features Model 716 Technical Specifications..................Patent Notice ........................Block Diagram ........................Section II - Installation Unpacking and Inspection ....................Mounting ..........................Rack Requirements - Heat Dissipation AC (Mains) Power ......................... - Page 4 Section IV - Calibration Calibration .......................... Equipment Required - Power Supply Check - Clock Set - Low-Pass Filter Matching - Crosstalk Trim - Separation Trim Section V - Circuit Descriptions Circuit Descriptions ......................Component Annotation - A PWM Primer - PWM Ramp Circuitry - Signal Path Circuitry - Input Stages - AGC Stage - Wideband Compression and Limiting - High Frequency Limiter - Filter Overshoot Compensator - Low-Pass Filter -...
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Page 5: Section I - Introduction
Section I INTRODUCTION MODEL 716 PRODUCT DESCRIPTION Inovonics introduced the first “DAVID” (as in David vs. Goliath) FM- General Stereo Processor/Generator in 1992. The original Model 715 was the hallmark of simplicity, and was intended to answer the more basic of FM radio broadcasting needs. -
Page 6: Patent Notice
Crosstalk (M S or S Compressor/Limiter: à à Processing OUT: nonlinear Fast-acting peak limiter with crosstalk –55dB or better. secondary “platform” time Processing IN: overall crosstalk constant to compress dynamic –50dB or better range with average-value weighting. Independent high Stereo Pilot: frequency limiter conforms to 19kHz, ±1Hz;... - Page 7 Figure 1 - Block Diagram, DAVID-II FM-Stereo Processor/Generator — —...
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Page 8: Section Ii - Installation
SERVICE OR MODIFICA- TION INSTRUCTIONS should they be issued by Inovonics. MOUNTING Inovonics’ DAVID-II is packaged to mount in a standard 19-inch Rack equipment rack and requires only 1¾ inches (1U) of vertical rack Requirement space. -
Page 9: Radio Frequency Interference (Rfi)
A mains voltage selector switch is located beneath the top cover of the Voltage Selector unit, adjacent to the AC mains connector on the circuit board. With primary AC power disconnected, slide the red actuator with a small screwdriver so that the proper mains voltage (115 or 230) is visible. You must always install an appropriate fuse, and should mark the rear- panel voltage/fuse designation. - Page 10 channels. Since these are “bridging” (high impedance) inputs, they provide no termination for the console or other equipment which feeds the DAVID-II. Please feel at liberty to connect a 600-ohm resistor across the input terminals should you feel this really necessary. Most professional equipment nowadays features low output impedances and high input impedances.
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Page 11: Pre-Emphasis Selection
PRE-EMPHASIS SELECTION The DAVID-II supports the 75-microsecond FM broadcasting pre- emphasis standard, common to the Western Hemisphere and parts of the Orient, and the 50-microsecond standard used in Europe and Asia. Pre-emphasis appropriate to the shipping destination is jumpered at the factory, but this is easily changed if necessary. -
Page 12: Bass-Enhance" Jumpering
reduction technique which employs a similar boost-before-cutoff at the high-frequency end of the spectrum. Figure 4 - “Bass-Enhance” Equalization Curve As delivered from the factory, “Bass-Enhance” equalization is defeated. “Bass-Enhance” To enable the “Bass-Enhance” equalizer, remove the top cover and Jumpering locate the first vertical row of integrated circuits closest to the right- hand side of the chassis, the one just behind the PROGRAM LINE... -
Page 13: Subcarrier Input
SUBCARRIER INPUT Internal combining is provided for an RDS or an SCA auxiliary subcarrier. The rear-panel SUBCARRIER INPUT connector is an unbalanced input with a load impedance in the neighborhood of 10K-ohms. An RDS subcarrier normally accounts for 5% or less of the total composite multiplex output signal, making it 26dB or more below peak program modulation. -
Page 14: Section Iii - Setup And Operation
Section III SETUP AND OPERATION PANEL CONTROLS AND INDICATORS A brief description of the front-panel controls and indicators is given here. Do scan this section to at least verify that our terminology agrees with yours. PLEASE NOTE that all front-panel multiturn trim controls require fifteen to twenty complete rotations of the adjusting screw to cover their total operating range. - Page 15 unnatural proportions. The green GATE OPEN indicator will remain continuously lighted during most music programming, but will blink off during pauses in speech. This is, in essence, a “drive” control at the input of the AVERAGE compressor/limiter stage, affording the user control COMPRESSION over program density.
- Page 16 In the fully-counterclockwise (OUT) position, an COMPOSITE output “safety” clipper catches only those very fast PROCESSING peaks and overshoots which sneak by the earlier protection circuitry. As the COMPOSITE PROCESSING control is rotated clockwise, the level applied to the safety clipper is increased by the dB value indicated on the front panel.
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Page 17: Normal Setup Procedure
the AUDIO PROCESSING switch in the IN position unless outboard provision is made for pre-emphasis and limiting. Without external pre-limiting, program material will be driven hard into the clipping circuits and result in egregious distortion.. The PILOT switch lets the user manually turn off the PILOT 19kHz stereo pilot for certain tests. - Page 18 1. To the left channel only, apply a 500Hz test tone from the console at a level 2.5dB above normal reference level. This is simply a console VU meter indication of +2.5VU. 2. Adjust the left channel (L) INPUT GAIN control so that both the 0dB and the –5dB AGC GAIN indicators light to equal brilliance.
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Page 19: Average Compression Adjustment
subcarrier level control) for the proper injection. This is normally about 5% for an RDS subcarrier, 10% for an SCA. 7. Put the Mod-Monitor back into its “Total Peak Modulation” measurement mode and, if necessary, trim the OUTPUT LEVEL control so that the peak flasher(s) indicate only occasional 100% peaks. - Page 20 Section IV CALIBRATION The upgrade to PWM processing has greatly simplified calibration of the DAVID-II when compared with its predecessor, the Model 715 DAVID. The number of trimmer adjustments under the top cover has been reduced from nineteen(!) to only eight. “Routine”...
- Page 21 The low-pass filter for the left program channel is not adjustable; Low-Pass Filter rather, it employs close-tolerance components to meet design Matching parameters. Since close frequency and phase response matching between stereo channels is essential to acceptable Stereo Generator crosstalk performance, trim controls have been included in the right channel filter so that it may be tuned to match left channel response.
- Page 22 9. Adjust R65 (between IC21 and IC22) for a right-channel null. NOTE: The third filter null is at approximately 34.5kHz. Rather than to match frequency response between channels at this point, the third filter adjustment is used to help match phase response in the next procedure.
- Page 23 difference” to balance crosstalk measurements, sacrificing a null at one frequency to improve that at the other. When this part of the Calibration Procedure has been successfully completed, the sub-channel measurement should remain below –50dB (relative to 100% modulation) as the Audio Generator is swept from 20Hz to 15kHz.
- Page 24 6. Adjust the equalization and phase trimmers, R56 and R57, for best stereo separation. There is some interaction between these two adjustments, but there will be only one setting of each which will give best separation. Null one, then the other, and back-and-forth, etc., until no further improvement can be had.
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Page 25: Circuit Descriptions
FET attenuators in its three distinct Control processing sections. This technology, as applied to broadcast audio processing, was pioneered by Inovonics in 1982. PWM is a simple, colorless, quasi-digital method of linear gain control which avoids the several hassles associated with more expensive, possibly single-sourced VCA ICs or matched and balanced FET devices. - Page 26 Switch ON Switch OFF Attenuation 100% 12dB 20dB 40dB Both the wideband and the independent high frequency compression/ Feedforward limiting circuits operate in a feedforward mode, rather than using the Control more traditional feedback method. The amplitude of the input signal establishes circuit gain to hold the output constant at a 100%- modulation “ceiling”...
- Page 27 characteristic. This means that the program signal eases gently into compression and limiting, avoiding the abrupt change from a linear to a limited state which characterizes traditional feedback topology. The “soft knee” is normal behavior for feedforward gain control, and is credited for the smoother, less fatiguing sound attributed to this method.
- Page 28 The negative-going pulse from Q9 triggers a similar event with Q6 and Q7. On the positive transition of the pulse, Q6 is turned off, allowing Q7 to turn on. C49 and R99 establish the off time for Q6, hence the on time for Q7.
- Page 29 SIGNAL PATH CIRCUITRY NOTE: Left and right program channel circuits are identical, so only the left channel will be described here. A skilled technician should find it within his capability to extrapolate for the right channel. INPUT STAGES IC44B is an “active-balancing” stage for the left channel program line Line Input input, affording rejection of unwanted common-mode signals.
- Page 30 IC49B is a simple unity-gain inverter. Along with diodes CR45 and DC Control CR46, it forms a full-wave rectifier for the left channel program signal. Signal Rectifier The right channel has an identical rectifier, and the resulting rectified voltage represents the higher level of the two channels. This voltage is used by the feedback-mode AGC and the feedforward compressor/ limiter.
- Page 31 corrected average program level. Moreover, the gating threshold is frequency-weighted for greatest sensitivity in the voice range. Gating is based on L+R energy. The left and right channels are summed by IC36B through R276 and R255. CR30 and CR29 comprise a full-wave rectifier at the input of comparator IC29B.
- Page 32 IC28D buffers the DC gain-controlling voltage and delivers it to comparator IC42A. The PWM squarewave from IC42A drives PWM attenuator IC46D. IC45B and IC37A comprise another 4-pole low-pass reconstruction filter to remove the 152kHz PWM switching component. IC28C is a slope detector sampling the wideband compressor/limiter Gain Reduction DC control voltage.
- Page 33 FILTER OVERSHOOT COMPENSATOR All low-pass filters exhibit a certain amount of overshoot and ringing Sources of when presented with complex input waveforms. Generally, the sharper Overshoot the cutoff, the more pronounced the effect. Overshoots result from the elimination of higher-order input signal components which, prior to filtering, helped define the signal peak amplitude.
- Page 34 the DAVID-II is sometimes called the “FDNR” because each of the legs to ground simulates a Frequency-Dependent Negative Resistance. Referring back to the classic L-C design, resistors in series with the signal replace series inductors, and each of the active circuits to ground replaces an inductor/capacitor series-resonant element.
- Page 35 In its OFF position, the front-panel PILOT switch, S3, is arranged to PILOT Switch interrupt the pilot sampling sequence and preset IC6 to a zero count. This stops the stereo pilot at its zero crossing. The FM-multiplex “composite” waveform consists of a “main” channel, Subcarrier conveying the L+R stereo sum in its normal audible frequency range, Generation...
- Page 36 IC18A is a combining stage for the main/sub portion of the composite Combining signal, the stereo pilot, and an optional RDS or SCA subcarrier applied Amplifier to the rear-panel SUBCARRIER INPUT jack. The front-panel OUTPUT LEVEL control, R13, is in the feedback path of IC18A, affording adjustment over the composite level delivered to the exciter.
- Page 37 Section VI APPENDIX The following section of this Manual contains Parts Lists for the Inovonics DAVID-II, Schematic Diagrams of all electronic circuitry, and an explanation of Inovonics’ Warranty Policy. — —...
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Page 38: Parts List
PARTS LIST EXPLANATION OF PARTS LISTINGS This section contains listings of component parts used in the Inovonics DAVID-II FM-Stereo Processor/Generator. These are listed either en- masse, or by schematic component reference designation, and may, or may not, specify a particular manufacturer. When no manufacturer is called-out, the term “open mfgr.”... - Page 39 CR1-6 Diode, Silicon Rectifier; (open mfgr.) 1N4005 CR7,10-47 Diode, Silicon Signal; (open mfgr.) 1N4151 or equiv. CR8,9 Diode, Schottky; (open mfgr.) 1N5711 Fuseholder, PC-mounting; Littlefuse 345-101-010 with 345-101-020 Cap for ¼-inch (U.S.) fuses, or 345-121-020 Cap for 5mm (European) fuses. (Fuse is normal “fast-blow” type in value specified on rear panel with reference to mains supply.) Ferrite Bead;...
- Page 40 Switch, Power Rocker; Carling RA 911-RB-O-N Power Transformer, PC-mounting; Signal LP-20-600 or direct cross- reference Crystal 1.216MHz; SPECIAL - Inovonics Part No. 1242 MAIL-ORDER COMPONENT SUPPLIERS The following electronic component distributors have proven to be reputable suppliers of both large and small quantities of parts. Any semiconductor, IC, capacitor, resistor or connector used in the DAVID-II is probably available from one or more of these firms.