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Audio Elect nics This Page Intentionally Left Blank Audio Electron ics Second edition John Linsley Hood Newnes O RD AUCKLAND BOSTON JOHA2q BURG MELBOU E W DELHI Newnes An imprint of Butterwo~h-Heinemann Linacre House, Jordan Hill, Oxt~rd OX2 8DP 225 Wildwood Avenue, Woburn, MA 01801-204 l A division of Reed Educational and Professional Publishing Ltd ~--~%. A member of the Reed Elsevier plc group First published 1995 Second edition 1999 Reprinted 2000 Transl~rred to digital printing 2004 ~# Chapters I-5 Butterworth-Heinemann 1993, 1995, 1998 Chapters ~ 11 John Linsley Hoo6 1995, 1999 All rights reserved. No pan of this publication may ~ reproduced in any material fo~ (including photocopying or storing in aw medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Lt~ 90 Tottenham Cou~ Road London, England W lP 0LR Applications for the copyright holder's written permission to reproduce any pa~ of this publication should be addressed to the publishers British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Libra,, Library of Congress Cataloguing in Publication Data A catalogue record for this book is available ~om the Library of Congress iSBN 0 7506 4332 3 Typeset by Genesis Typesetting, RochesteL Kent DL/ NT A 1 E ~C~ E~R¥ T~ TNAT WE Pb~$H, Bb~ERWO~It°HEiNEMANN W|U~ PAY FC~ B~CV TO ~.~tT ~ ~M~ F~ A TRY. Contents Preface xi 1 Tape recording The basic system Magnetic tape Tape coatings; Tape backing materials; Tape thicknesses; Tape widths The recording process Causes of non-uniform frequency response Influence of HF bias; Head gap effects; Pole-piece contour effects; Effect of tape speed Record/replay equalisation Pre- and de-emphasis; Frequency correction standards Head design 12 Magnetic materials; Tape erasure Recording track dimensions 18 HF bias 19 Basic bias requirements; Bias frequency; Bias waveform; Optimum bias level; Maximum output level (MOL); Sensitivity; Harmonic distortion; Noise level; Saturation output level (SOL); Bias level setting The tape transport mechanism 25 Transient performance 26 Tape noise 27 Electronic circuit design 30 Record/replay circuit design; Schematic layout; Sony; Pioneer; Technics Replay equalisation 34 Bias oscillator circuits 36 The record amplifier 39 Input/output stage design Recording level indication 41 Tape drive motor speed control 42 Professional recording equipment 42 General description 43 Mechanical aspects; Electrical design Multi-track machines 47 vi Contents Digital recording systems 8 PCM encoding; Bandwidth requirements; Analogue vs. digital performance; Editing; Domestic equipment; Copy protection (SCMS); Domestic systems; RDAT, SDAT, CDR, Mini-disc, DCC 2 Tuners and radio receivers 57 Background 57 Basic requirements 57 Transmitter radiation pattern The influence of the ionosphere 58 Critical frequency; Classification of radio spectrum; VHF/SHF effects Why VHF transmissions? 63 Broadcast band allocations; Choice of broadcasting frequency AM or FM? 64 Modulation systems; Bandwidth requirements FM broadcast standards 66 Stereo encoding/decoding 66 GE/Zenith 'pilot tone' system 66 Decoder systems PCM programme distribution system 70 HF pre-ernphasis Supplementary broadcast signals 75 Alternative transmission methods 75 SSB broadcasting 76 Radio receiver design 79 Tuned circuit characteristics; SAW filters; Superhet receiver; Sensitivity; Stability; Crystal control; Barlow- Wadley loop; Frequency synthesis; Phase-locked loop; Automatic frequency control; Frequency meter display; FM linearity; FM demodulator types; AM linearity; AM demodulator systems Circuit design 114 New developments 116 Appendices 117 Broadcast signal characteristics; Radio data system (RDS) 3 Preamplifiers and input signals 119 Requirements 119 Signal voltage and impedance levels 119 Contents vii Gramophone pick-up inputs 120 Ceramic cartridges; DIN input connections; MM and variable reluctance cartridges; RIAA equalisation; MC cartridges Input circuitry 123 Moving coil PU head amplifier design 127 Circuit arrangements 128 Noise levels; Low noise IC op. amps Input connections 135 Input switching 136 Bipolar transistor; FET Diode 4 Voltage amplifiers and controls 140 Preamplifier stages 140 Linearity 140 Bipolar transistors; Field effect devices; MOSFETs U, V and T types; MOSFET breakdown Noise levels 149 Output voltage characteristics 150 Voltage amplifier design 151 Constant-current sources and 'current mirrors' 154 Performance standards 159 Audibility of distortion 162 Transient defects; TID and slew-rate limiting; Spurious signals and interference General design considerations 168 Controls 169 Gain controls; Tone controls; Baxandall; Slope; Clapham junction; Parametric; Graphic equaliser; Quad tilt control; Channel balance and separation controls; Filter circuitry $ Power output stages 189 Valve amplifier designs 189 Early transistor circuits 192 Listener fatigue and crossover distortion 192 The LIN circuit Improved transistor amplifier designs 195 Power MOSFETs 196 Operating characteristics; V and U types Output transistor protection 201 Safe operating area (SOAR) Power output and power dissipation 203 General design considerations 206 Bode Plot viii Contents Slew-rate limiting and TID 207 HF stabilisation Advanced amplifier designs 211 Stabilised power supplies; Output stage configurations Alternative design approaches 219 The 'Blomley' circuit; The 'Quad' current dumping amplifier; Feed-forward systems; The 'Sandman' circuit Contemporary amplifier design practice 227 The 'Technics' SE-A100 circuit Sound quality and specifications 229 Design compromises; Measurement systems; Conclusions 6 The compact disc and digital audio 233 Why use digital techniques? 233 Problems with digital encoding 234 Signal degradation during copying; Pulse code modulation; Quantisation errors; Encoding resolution; Bandwidth and sampling frequency; Distortion; Error detection and correction; Filtering; Aliasing; PCM spectrum The record-replay system 239 Recording system layout; Analogue to digital conversion (ADC) The replay system 245 Physical characteristics; Optical readout; CD performance and disc statistics; Two-beam vs. three-beam readout methods; 0-1 digit generation; Replay electronics; Zero- signal muting; Eight to fourteen modulation; Digital to analogue conversion; Precision required; Dynamic element matching; Digital filtering and oversampling; Finite impulse response filters; Transversal filters; Attenuation characteristics; Interpolation of sample values; Dither; Effect on resolution; The Bitstream process; Low resolution decoding; Noise shaping Error correction 260 Reed-Solomon Code (CIRC) techniques; Error detection; Addition of parity bits; Interleaving; Faulty bit/word replacement; CIRC performance 7 Test Instruments and measurements 265 Instrument types 266 Distortion types; Measurements vs. subjective testing; Types of test instruments Contents ix Signal generators 266 Sinewave oscillators; Wien bridge oscillators; Required frequency range; Waveform purity requirements; Amplitude stabilisation; Square-wave generation; Output settling time; Very low distortion circuitry; Parallel-T oscillator designs; Digital waveform synthesis; Frequency stable systems; Phase-locked loop techniques; Function generators Alternative waveform types 277 Square-wave testing Distortion measurement 284 THD meters; Intermodulation distortion measurement; Spectrum analysis; FFT analysis Oscilloscopes 294 Method of operation; Sensitivity and scan speeds; Multiple trace displays; Time-base synchronisation; External X-axis inputs; Lissajoux figures; Use with stereo signals; X-axis signal outputs; Digital storage types; Resolution 8 Loudspeaker crossover systems 305 Why necessary? 305 Cone design 306 Optimum frequency span for LS drivers; Effects of LS diaphragm flexure; Acoustic mismatch at diaphragm surround; LS diaphragm types; Flat piston vs. conical form; Rigid cone systems; Coil attachment and magnet characteristics Soundwave dispersion 309 Crossover system design 309 Effects of output superposition Crossover component types 315 LS output equalisation 316 Active crossover systems 317 Active filter design 319 Bi-amplification and tri-amplification Bi-wiring and tri-widng 322 Loudspeaker connecting cables 9 Power supplies 324 The importance of the power supply unit 324 Rejection of hum and noise; Single-ended and balanced systems Contents Circuit layouts 326 Valve vs. solid state rectifiers; Effect of size of reservoir capacitor; Peak charging currents Circuit problems 328 Full-wave rectifier systems 328 Half-wave vs. full-wave rectification; Rectifier circuits; Reservoir capacitor optimum size Transformer types and power ratings 332 Output DC voltage; Stacked lamination vs. toroidal types Stabilised PSU circuits 333 Zener diodes; Bandgap reference sources; Three-terminal PSU ICs; Effect of PSU on musical performance; 'Music power' ratings; Output circuit protection; Higher power regulator layouts; Shunt vs. series systems; PSU output impedance; Designs in commercial equipment Commercial power amp. PSUs 337 Output source impedance and noise 338 Battery supplies Transformer noise and stray magnetic fields 341 10 Noise reduction techniques 342 Bandwidth limitation 342 Pre-emphasis 343 'Noise masking' and
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