Audio Electronics

389 Pages·1999·14.327 MB·English

by  J. Hood

Audio Elect nics
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Audio Electron ic s
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
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iSBN 0 7506 4332 3
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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