The Design of
Active Crossovers
The use of active crossovers is increasing. They are used by almost every sound reinforcement system, and by almost every recording studio monitoring set-up. There is also a big usage of active crossovers in car audio, with the emphasis on routing the bass to enormous low-frequency loudspeakers. Active crossovers are used to a small but rapidly growing extent in domestic hifi, and I argue that their widespread introduction may be the next big step in this field.
The Design of Active Crossovers has now been updated and extended for the Second Edition, taking in developments in loudspeaker technology and crossover design. Many more pre-designed filters are included so that crossover development can be faster and more certain, and the result will have a high performance. The Second Edition continues the tradition of the first in avoiding complicated algebra and complex numbers, with the mathematics reduced to the bare minimum; there is nothing more complicated to grapple with than a square root.
New features of the Second Edition include:
•More on loudspeaker configurations and their crossover requirements: MTM Mid-Tweeter-Mid configurations (The d’Appolito arrangement) Line arrays (J arrays) for sound reinforcement
Frequency tapering Band zoning Power tapering
Constant-Beamwidth Transducer (CBT) loudspeaker arrays
•More on specific sound-reinforcement issues like the loss of high frequencies due to the absorption of sound in air and how it varies.
•Lowpass filters now have their own separate chapter.
Much more on third, fourth, fifth, and sixth-order lowpass filters.
Many more examples are given with component values ready-calculated
•Highpass filters now have their own separate chapter, complementary to the chapter on lowpass filters.
Much more on third, fourth, fifth, and sixth-order highpass filters.
Many more examples are given with component values ready-calculated
•Anew chapter dealing with filters other than the famous Sallen & Key type. New filter types are introduced such as the third-order multiple feedback filter.
There is new information on controlling the Q and gain of state-variable filters.
•More on the performance of crossover filters, covering noise, distortion, and the internal overload problems of filters.
•The chapter on bandpass and notch filters is much extended, with in-depth coverage of the Bainter filter, which can produce beautifully deep notches without precision components or adjustment.
•Much more information on the best ways to combine standard components to get very accurate non-standard values. Not only can you get a very accurate nominal value, but also the effective tolerance of the combination can be significantly better than that of the individual components used. There is no need to keep huge numbers of resistor and capacitor values in stock.
•More on low-noise high-performance balanced line inputs for active crossovers, including versions that give extraordinarily high common-mode rejection. (noise rejection)
•Two new appendices giving extensive lists of crossover patents, and crossover-based articles in journals.
This book is packed full of valuable information, with virtually every page revealing nuggets of specialized knowledge never before published. Essential points of theory bearing on practical performance are lucidly and thoroughly explained, with the mathematics kept to an essential minimum.
Douglas’background in design for manufacture ensures he keeps a very close eye on the cost of things.
Douglas Self studied engineering at Cambridge University, then psychoacoustics at Sussex University.
He has spent many years working at the top level of design in both the professional audio and hi-fi industries and has taken out a number of patents in the field of audio technology. He currently acts as a consultant engineer in the field of audio design.
Douglas Self maintains a website at douglas-self.com
The Design of
Active Crossovers
Second Edition
Douglas Self
Second edition published 2018 by Routledge
711 Third Avenue, New York, NY 10017
and by Routledge
2 Park Square, Milton Park, Abingdon, Oxon, OX14 4RN
Routledge is an imprint of the Taylor & Francis Group, an informa business
© 2018 Taylor & Francis
The right of Douglas Self to be identified as author of this work has been asserted by him in accordance with sections 77 and 78 of the Copyright, Designs and Patents Act 1988.
All rights reserved. No part of this book may be reprinted or reproduced or utilised in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the publishers.
Trademark notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe.
First edition published by Focal Press 2011
Library of Congress Cataloging-in-Publication Data
Names: Self, Douglas, author.
Title: The design of active crossovers / Douglas Self. Description: Second edition. | New York, NY : Routledge, 2018.
Identifiers: LCCN 2017048835 | ISBN 9781138733022
(hardback : alk. paper) | ISBN 9781138733039 (pbk. : alk. paper) | ISBN 9781315187891 (ebook)
Subjects: LCSH: Electric filters,Active—Design and construction. | Bridge circuits—Design and construction.
Classification: LCC TK7872.F5 S447 2018 | DDC 621.3815/324—dc23 LC record available at https://lccn.loc.gov/2017048835
ISBN: 978-1-138-73302-2 (hbk)
ISBN: 978-1-138-73303-9 (pbk)
ISBN: 978-1-315-18789-1 (ebk)
Typeset in Times New Roman by Apex CoVantage, LLC
To Julie, with all my love
Contents
Acknowledgments xxi Preface xxiii
Chapter 1: Crossover Basics 1
What a Crossover Does 1 Why a Crossover Is Necessary 1 Beaming and Lobing 2 Passive Crossovers 4 Active Crossover Applications 5 Bi-Amping and Bi-Wiring 6 Loudspeaker Cables 8 The Advantages and Disadvantages of Active Crossovers 9
The Advantages of Active Crossovers 9 Some IllusoryAdvantages ofActive Crossovers 13
The Disadvantages of Active Crossovers 14
The Next Step in Hi-Fi 16 Active Crossover Systems 16 Matching Crossovers and Loudspeakers 20 A Modest Proposal: Popularising Active Crossovers 21 Multi-Way Connectors 22 Subjectivism 23
Chapter 2: How Loudspeakers Work 25
Sealed-Box Loudspeakers 26 Reflex (Ported) Loudspeakers 27 Auxiliary Bass Radiator (ABR) Loudspeakers 28 Transmission Line Loudspeakers 28 Horn Loudspeakers 29 Electrostatic Loudspeakers 29 Ribbon Loudspeakers 30 Electromagnetic Planar Loudspeakers 30 Air-Motion Transformers 31 Plasma Arc Loudspeakers 31 The Rotary Woofer 32 MTM Tweeter-Mid Configurations (d’Appolito) 33
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Contents
Vertical Line Arrays 34
Line Array Amplitude Tapering 37
Line Array Frequency Tapering 37
CBT Line Arrays 39 Diffraction 39 Sound Absorption in Air 44 Modulation Distortion 46 Drive Unit Distortion 47 Doppler Distortion 48 Further Reading on Loudspeaker Design 49
Chapter 3: Crossover Requirements 51
General Crossover Requirements 51
1 Adequate Flatness of Summed Amplitude/Frequency Response On-Axis 51 2 Sufficiently Steep Roll-Off Slopes Between the Filter Outputs 51 3 Acceptable Polar Response 52 4 Acceptable Phase Response 53
5 Acceptable Group Delay Behaviour 53
Further Requirements for Active Crossovers 54
1 Negligible Extra Noise 54 2 Negligible Impairment of System Headroom 55 3 Negligible Extra Distortion 55 4 Negligible Impairment of Frequency Response 56
5 Negligible Impairment of Reliability 56
Linear Phase 56 Minimum Phase 57 Absolute Phase 57 Phase Perception 58 Target Functions 59
Chapter 4: Crossover Types 61
All-Pole and Non-All-Pole Crossovers 61 Symmetric and Asymmetric Crossovers 62 Allpass and Constant-Power Crossovers 62 Constant-Voltage Crossovers 63 First-Order Crossovers 63 First-Order Solen Split Crossover 69 First-Order Crossovers: 3-Way 70 Second-Order Crossovers 70
Second-Order Butterworth Crossover 71 Second-Order Linkwitz-Riley Crossover 78 Second-Order Bessel Crossover 79 Second-Order 1.0 dB-Chebyshev Crossover 80
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Contents
Third-Order Crossovers 83
Third-Order Butterworth Crossover 84 Third-Order Linkwitz-Riley Crossover 86 Third-Order Bessel Crossover 89 Third-Order 1.0 dB-Chebyshev Crossover 89
Fourth-Order Crossovers 92
Fourth-Order Butterworth Crossover 93 Fourth-Order Linkwitz-Riley Crossover 95 Fourth-Order Bessel Crossover 99 Fourth-Order 1.0 dB-Chebyshev Crossover 99 Fourth-Order Linear-Phase Crossover 101 Fourth-Order Gaussian Crossover 103 Fourth-Order Legendre Crossover 106
Higher-Order Crossovers 108 Determining Frequency Offsets 109 Filler-Driver Crossovers 111 The Duelund Crossover 113 Crossover Topology 113 Crossover Conclusions 118
Chapter 5: Notch Crossovers 121
Elliptical Filter Crossovers 121 Neville Thiele MethodTM (NTM) Crossovers 125
Chapter 6: Subtractive Crossovers 131
Subtractive Crossovers 131 First-Order Subtractive Crossovers 132 Second-Order Butterworth Subtractive Crossovers 133 Third-Order Butterworth Subtractive Crossovers 135 Fourth-Order Butterworth Subtractive Crossovers 135 Subtractive Crossovers With Time Delays 137 Performing the Subtraction 141
Chapter 7: Lowpass and Highpass Filter Characteristics 145
Active Filters 145 Lowpass Filters 146 Highpass Filters 146 Bandpass Filters 146 Notch Filters 146 Allpass Filters 147 All-Stop Filters 147 Brickwall Filters 147 The Order of a Filter 147
ix
Contents
Filter Cutoff Frequencies and Characteristic Frequencies 148 First-Order Filters 148 Second-Order and Higher-Order Filters 149 Filter Characteristics 149
Amplitude Peaking and Q 150 Butterworth Filters 151 Linkwitz-Riley Filters 153 Bessel Filters 155 Chebyshev Filters 160 1 dB-Chebyshev Lowpass Filter 162
3 dB-Chebyshev Lowpass Filter 162
Higher-Order Filters 167
Butterworth Filters up to 8th-Order 168 Linkwitz-Riley Filters up to 8th-Order 172 Bessel Filters up to 8th-Order 173
Chebyshev Filters up to 8th-Order 175
More Complex Filters—Adding Zeros 176
Inverse Chebyshev Filters (Chebyshev Type II) 177
Elliptical Filters (Cauer Filters) 179
Some Lesser-Known Filter Characteristics 182
Transitional Filters 182 Linear-Phase Filters 182 Gaussian Filters 184 Legendre-Papoulis Filters 187 Laguerre Filters 190
Synchronous Filters 190
Other Filter Characteristics 193
Chapter 8: Designing Lowpass Filters: Sallen & Key 195
Designing Real Filters 195 Component Sensitivity 195 First-Order Lowpass Filters 197 Second-Order Filters 198 Sallen & Key 2nd-Order Lowpass Filters 198 Sallen & Key Lowpass Filter Components 199 Sallen & Key 2nd-Order Lowpass: Unity Gain 199
Sallen & Key 2nd-Order Lowpass Unity Gain: Component Sensitivity 202 Filter Frequency Scaling 202 Sallen & Key 2nd-Order Lowpass: Equal Capacitor 204
Sallen & Key 2nd-Order Lowpass Equal-C: Component Sensitivity 206 Sallen & Key 2nd-Order Butterworth Lowpass: Defined Gains 207 Sallen & Key 2nd-Order Lowpass: Non-Equal Resistors 207
Sallen & Key 2nd-Order Lowpass: Optimisation 209
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Contents
Sallen & Key 3rd-Order Lowpass: Two Stages 209 Sallen & Key 3rd-Order Lowpass: Single Stage 210
Sallen & Key 3rd-Order Lowpass in a Single Stage: Non-Equal Resistors 214
Sallen & Key 4th-Order Lowpass: Two Stages 215 Sallen & Key 4th-Order Lowpass: Single-Stage Butterworth 217 Sallen & Key 4th-Order Lowpass: Single-Stage Linkwitz-Riley 221 Sallen & Key 4th-Order Lowpass: Single Stage With
Non-Equal Resistors 224
Sallen & Key 4th-Order Lowpass: Single Stage With Other
Filter Characteristics 224 Sallen & Key 5th-Order Lowpass: Three Stages 225 Sallen & Key 5th-Order Lowpass: Two Stages 228 Sallen & Key 5th-Order Lowpass: Single Stage 229 Sallen & Key 6th-Order Lowpass: Three Stages 230 Sallen & Key 6th-Order Lowpass: Single Stage 232 Sallen & Key Lowpass: Input Impedance 234 Linkwitz-Riley Lowpass With Sallen & Key Filters: Loading Effects 234
Lowpass Filters With Attenuation 236 Bandwidth Definition Filters 237 Bandwidth Definition: Butterworth Versus Bessel 237 Variable-Frequency Lowpass Filters: Sallen & Key 239
Chapter 9: Designing Highpass Filters 241
First-Order Highpass Filters 241 Sallen & Key 2nd-Order Filters 242 Sallen & Key 2nd-Order Highpass Filters 242 Sallen & Key Highpass Filter Components 243 Sallen & Key 2nd-Order Highpass: Unity Gain 243 Sallen & Key 2nd-Order Highpass: Equal Resistors 244
Sallen & Key 2nd-Order Butterworth Highpass: Defined Gains 245 Sallen & Key 2nd-Order Highpass: Non-Equal Capacitors 247
Sallen & Key 3rd-Order Highpass: Two Stages 248 Sallen & Key 3rd-Order Highpass in a Single Stage 249 Sallen & Key 4th-Order Highpass: Two Stages 251 Sallen & Key 4th-Order Highpass: Butterworth in a Single Stage 252 Sallen & Key 4th-Order Highpass: Linkwitz-Riley in a Single Stage 254 Sallen & Key 4th-Order Highpass: Single-Stage With Other
Filter Characteristics 256 Sallen & Key 5th-Order Highpass: Three Stages 257 Sallen & Key 5th-Order Butterworth Filter: Two Stages 259 Sallen & Key 5th-Order Highpass: Single Stage 260 Sallen & Key 6th-Order Highpass: Three Stages 260 Sallen & Key 6th-Order Highpass: Single Stage 262
xi
Contents
Sallen & Key Highpass: Input Impedance 262 Bandwidth Definition Filters 262 Bandwidth Definition: Subsonic Filters 263 Bandwidth Definition: Combined Ultrasonic and Subsonic Filters 264 Variable-Frequency Highpass Filters: Sallen & Key 267
Chapter 10: Other Lowpass and Highpass Filters 271
Designing Filters 271 Multiple-Feedback Filters 272 Multiple-Feedback 2nd-Order Lowpass Filters 273 Multiple-Feedback 2nd-Order Highpass Filters 274 Multiple-Feedback 3rd-Order Filters 274
Multiple-Feedback 3rd-Order Lowpass Filters 275
Multiple-Feedback 3rd-Order Highpass Filters 275
Biquad Filters 276 Akerberg-Mossberg Lowpass Filter 276 Akerberg-Mossberg Highpass Filters 279 Tow-Thomas Biquad Lowpass and Bandpass Filter 280 Tow-Thomas Biquad Notch and Allpass Responses 285 Tow-Thomas Biquad Highpass Filter 286 State-Variable Filters 288 Variable-Frequency Filters: State-Variable 2nd Order 292 Variable-Frequency Filters: State-Variable 4th-Order 293 Variable-Frequency Filters: Other Orders of State-Variable 295 Other Filters 296
Chapter 11: Lowpass and Highpass Filter Performance 297
Aspects of Filter Performance: Noise and Distortion 297 Distortion in Active Filters 297
Distortion in Sallen & Key Filters: The DistortionAggravation Factor 298 Distortion in Sallen & Key Filters: Looking for DAF 303 Distortion in Sallen & Key Filters: 2nd-Order Lowpass 305 Distortion in Sallen & Key Filters: 2nd-Order Highpass 308 Mixed Capacitors in Low-Distortion 2nd-Order Sallen & Key Filters 310 Distortion in Sallen & Key Filters: 3rd-Order Lowpass Single Stage 311 Distortion in Sallen & Key Filters: 3rd-Order Highpass Single Stage 312 Distortion in Sallen & Key Filters: 4th-Order Lowpass Single Stage 314 Distortion in Sallen & Key Filters: 4th-Order Highpass Single Stage 317 Distortion in Sallen & Key Filters: Simulations 318 Distortion in Sallen & Key Filters: Capacitor Conclusions 320
Distortion in Multiple-Feedback Filters: The Distortion Aggravation Factor 321 Distortion in Multiple-Feedback Filters: 2nd-Order Lowpass 322 Distortion in Multiple-Feedback Filters: 2nd-Order Highpass 323
xii
Contents
Distortion in Tow-Thomas Filters: 2nd-Order Lowpass 324 Distortion in Tow-Thomas Filters: 2nd-Order Highpass 326 Noise in Active Filters 327 Noise and Bandwidth 328 Noise in Sallen & Key Filters: 2nd-Order Lowpass 329 Noise in Sallen & Key Filters: 2nd-Order Highpass 330 Noise in Sallen & Key Filters: 3rd-Order Lowpass Single Stage 330 Noise in Sallen & Key Filters: 3rd-Order Highpass Single Stage 330 Noise in Sallen & Key Filters: 4th-Order Lowpass Single Stage 331 Noise in Sallen & Key Filters: 4th-Order Highpass Single Stage 331
Noise in Multiple-Feedback Filters: 2nd-Order Lowpass 331 Noise in Multiple-Feedback Filters: 2nd-Order Highpass 332 Noise in Tow-Thomas Filters 332
Chapter 12: Bandpass and Notch Filters 333
Multiple-Feedback Bandpass Filters 333 High-Q Bandpass Filters 334 Notch Filters 335 The Twin-T Notch Filter 336 The 1-Bandpass Notch Filter 337 The Bainter Notch Filter 337
Bainter Notch Filter Design 339 Bainter Notch Filter Example 341 An Elliptical Filter Using a Bainter Highpass Notch 342
The Bridged-Differentiator Notch Filter 342 Boctor Notch Filters 343 Other Notch Filters 345 Simulating Notch Filters 345
Chapter 13: Time-Delay Filters 347
The Requirement for Delay Compensation 347 Calculating the Required Delays 349 Signal Summation 352 Physical Methods of Delay Compensation 353 Delay Filter Technology 355 Sample Crossover and Delay Filter Specification 355 Allpass Filters in General 355 First-Order Allpass Filters 356 Distortion and Noise in 1st-Order Allpass Filters 361 Cascaded 1st-Order Allpass Filters 363 Second-Order Allpass Filters 364 Distortion and Noise in 2nd-Order Allpass Filters 368 Third-Order Allpass Filters 369
xiii
Contents
Distortion and Noise in 3rd-OrderAllpass Filters 370 Higher-Order Allpass Filters 373 Delay Lines for Subtractive Crossovers 379 Variable Allpass Time Delays 381 Lowpass Filters for Time Delays 382
Chapter 14: Equalisation 385
The Need for Equalisation 385 What Equalisation Can and Can’t Do 386 Loudspeaker Equalisation 387 1 Drive Unit Equalisation 387 2 6 dB/octave Dipole Equalisation 388 3 Bass Response Extension 388 4 Diffraction Compensation Equalisation 389 5 Room Interaction Correction 390 Equalisation Circuits 393 HF-Boost and LF-Cut Equaliser 393 HF-Cut and LF-Boost Equaliser 395 Combined HF-Boost and HF-Cut Equaliser 398 Adjustable Peak/Dip Equalisers: Fixed Frequency and Low Q 398 Adjustable Peak/Dip Equalisers: Variable Centre Frequency and Low Q 400
Adjustable Peak/Dip Equalisers With High Q 402 Parametric Equalisers 405 The Bridged-T Equaliser 406 The Biquad Equaliser 407 Capacitance Multiplication for the Biquad Equaliser 414 Equalisers With Non-Standard Slopes 415
Equalisers With −3 dB/Octave Slopes 415 Equalisers With −3 dB/Octave Slopes Over Limited Range 419
Equalisers With −4.5 dB/Octave Slopes 420
Equalisers With Other Slopes 420
Equalisation by Filter Frequency Offset 421 Equalisation byAdjustingAll Filter Parameters 422
Chapter 15: Passive Components for Active Crossovers 425
Component Values 425 Resistors 425
Through-Hole Resistors 426
Surface-Mount Resistors 427
Resistors: Values and Tolerances 428
ImprovingAccuracy With Multiple Components: Gaussian Distribution 431
Resistor Value Distributions 435
xiv
Contents
ImprovingAccuracy With Multiple Components: Uniform Distribution 437
Obtaining Arbitrary Resistance Values 438 Other Resistor Combinations 439 Resistor Noise: Johnson and Excess Noise 441 Resistor Non-Linearity 443 Capacitors: Values and Tolerances 445 Obtaining Arbitrary Capacitance Values 446 Capacitor Shortcomings 447 Non-Electrolytic Capacitor Non-Linearity 449 Electrolytic Capacitor Non-Linearity 454
Chapter 16: Opamps for Active Crossovers 459
Active Devices for Active Crossovers 459 Opamp Types 460 Opamp Properties: Noise 460 Opamp Properties: Slew Rate 462 Opamp Properties: Common-Mode Range 463 Opamp Properties: Input Offset Voltage 463 Opamp Properties: Bias Current 463 Opamp Properties: Cost 464 Opamp Properties: Internal Distortion 465 Opamp Properties: Slew Rate Limiting Distortion 466 Opamp Properties: Distortion Due to Loading 466 Opamp Properties: Common-Mode Distortion 467 Opamps Surveyed 468 The TL072 Opamp 469 The NE5532 and 5534 Opamps 471
The 5532 With Shunt Feedback 471 5532 Output Loading in Shunt-Feedback Mode 472 The 5532 With Series Feedback 474 Common-Mode Distortion in the 5532 474 Reducing 5532 Distortion by Output Stage Biasing 477 Which 5532? 482
The 5534 Opamp 483
The LM4562 Opamp 485
Common-Mode Distortion in the LM4562 486
The LME49990 Opamp 489
Common-Mode Distortion in the LME49990 491
The AD797 Opamp 492
Common-Mode Distortion in the AD797 494
The OP27 Opamp 494 Opamp Selection 497
xv
Contents
Chapter 17: Active Crossover System Design 499
Crossover Features 499
Input Level Controls 499 Subsonic Filters 499 Ultrasonic Filters 500 Output Level Trims 500 Output Mute Switches, Output Phase-Reverse Switches 500 Control Protection 500
Features Usually Absent 501
Metering 501 Relay Output Muting 501
Switchable Crossover Modes 501 Noise, Headroom, and Internal Levels 503 Circuit Noise and Low-Impedance Design 504 Using Raised Internal Levels 504 Placing the Output Attenuator 506 The Amplitude/Frequency Distribution of Musical Signals and
Internal Levels 507 Gain Structures 510 Noise Gain 513 Active Gain Controls 514 Filter Order in the Signal Path 516 Output Level Controls 518 Mute Switches 519 Phase-Invert Switches 520 Distributed Peak Detection 520 PowerAmplifier Considerations 522
Chapter 18: Subwoofer Crossovers 525
Subwoofer Applications 525 Subwoofer Technologies 525
Sealed-Box (Infinite Baffle) Subwoofers 526 Reflex (Ported) Subwoofers 527 Auxiliary Bass Radiator (ABR) Subwoofers 527 Transmission Line Subwoofers 528 Bandpass Subwoofers 528 Isobaric Subwoofers 529 Dipole Subwoofers 529 Horn-Loaded Subwoofers 530
Subwoofer Drive Units 530 Hi-Fi Subwoofers 530 Home Entertainment Subwoofers 531
Low-Level Inputs (Unbalanced) 532
xvi
Contents
Low-Level Inputs (Balanced) 532 High-Level Inputs 532 High-Level Outputs 533 Mono Summing 533 LFE Input 533 Level Control 533 Crossover In/Out Switch 534 Crossover Frequency Control (Lowpass Filter) 534 Highpass Subsonic Filter 534 Phase Switch (Normal/Inverted) 534 Variable Phase Control 535 Signal Activation Out of Standby 535
Home Entertainment Crossovers 535
Fixed Frequency 536 Variable Frequency 536
Multiple Variable 536
PowerAmplifiers for Home Entertainment Subwoofers 536 Subwoofer Integration 537 Sound-Reinforcement Subwoofers 538
Line or Area Arrays 539
Cardioid Subwoofer Arrays 539
Aux-Fed Subwoofers 539 Automotive Audio Subwoofers 540
Chapter 19: Motional Feedback Loudspeakers 543
Motional Feedback Loudspeakers 543 History 544 Feedback of Position 544 Feedback of Velocity 545 Feedback of Acceleration 548 Other MFB Speakers 551 Published Projects 552 Conclusions 552
Chapter 20: Line Inputs 555
External Signal Levels 555 Internal Signal Levels 555 InputAmplifier Functions 556 Unbalanced Inputs 556 Balanced Interconnections 559 TheAdvantages of Balanced Interconnections 560 The Disadvantages of Balanced Interconnections 560 Balanced Cables and Interference 560 Balanced Connectors 562
xvii
Contents
Balanced Signal Levels 563 Electronic vs Transformer Balanced Inputs 563 Common-Mode Rejection Ratio (CMRR) 563 The Basic Electronic Balanced Input 565 Common-Mode Rejection Ratio: Opamp Gain 568 Common-Mode Rejection Ratio: Opamp Frequency Response 569 Common-Mode Rejection Ratio: Opamp CMRR 570 Common-Mode Rejection Ratio:Amplifier Component Mismatches 571 APractical Balanced Input 573 Variations on the Balanced Input Stage 576 Combined Unbalanced and Balanced Inputs 576 The Superbal Input 577 Switched-Gain Balanced Inputs 578 Variable-Gain Balanced Inputs 580 The Self Variable-Gain Balanced Input 581 High Input Impedance Balanced Inputs 582 The InstrumentationAmplifier 583 InstrumentationAmplifierApplications 584 The InstrumentationAmplifier With 4x Gain 585 The InstrumentationAmplifier at Unity Gain 588 Transformer Balanced Inputs 590 Input Overvoltage Protection 592 Noise and Balanced Inputs 593 Low-Noise Balanced Inputs 593 Low-Noise Balanced Inputs in Real Life 598 Ultra-Low-Noise Balanced Inputs 598
Chapter 21: Line Outputs 603
Unbalanced Outputs 603 Zero-Impedance Outputs 604 Ground-Cancelling Outputs 605 Balanced Outputs 606 Transformer Balanced Outputs 607 Output Transformer Frequency Response 608 Transformer Distortion 609 Reducing Transformer Distortion 611
Chapter 22: Power Supply Design 615
Opamp Supply Rail Voltages 615 Designing a ±15 V Supply 616 Designing a ±17 V Supply 619 Using Variable-Voltage Regulators 620 Improving Ripple Performance 621
xviii
Contents
Dual Supplies From a Single Winding 622 Mutual Shutdown Circuitry 623 Power Supplies for Discrete Circuitry 624
Chapter 23: An Active Crossover Design 625
Design Principles 625 Example Crossover Specification 625 The Gain Structure 626 Resistor Selection 627 Capacitor Selection 627 The Balanced Line Input Stage 627 The Bandwidth Definition Filter 628 The HF Path: 3 kHz Linkwitz-Riley Highpass Filter 628 The HF Path: Time-Delay Compensation 631 The MID Path: Topology 632 The MID Path: 400 Hz Linkwitz-Riley Highpass Filter 633 The MID Path: 3 kHz Linkwitz-Riley Lowpass Filter 634 The MID Path: Time-Delay Compensation 634 The LF Path: 400 Hz Linkwitz-Riley Lowpass Filter 635 The LF Path: No Time-Delay Compensation 636 Output Attenuators and Level Trim Controls 636 Balanced Outputs 638 Crossover Programming 638 NoiseAnalysis: Input Circuitry 639 Noise Analysis: HF Path 640 NoiseAnalysis: MID Path 641 Noise Analysis: LF Path 642 Improving the Noise Performance: The MID Path 642 Improving the Noise Performance: The Input Circuitry 643 The Noise Performance: Comparisons With PowerAmplifier Noise 646
Conclusion 647
Appendix 1 Crossover Design References 649 Appendix 2 US Crossover Patents 653 Appendix 3 Crossover and Loudspeaker Articles in Wireless World/
Electronics World 655 Appendix 4 Loudspeaker Design References 657 Appendix 5 Component Series E3 to E96 659 Index 661
xix
