Jones Valve Amplifiers

4. Auflage 2011
ISBN: 978-0-08-096641-0
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 700 Seiten

Valve Amplifiers has been recognized as the most comprehensive guide to valve amplifier design, analysis, modification and maintenance. It provides a detailed presentation of the rudiments of electronics and valve design for engineers and non-experts. The source also covers design principles and construction techniques to help end users build their own tool from scratch designs that work. The author's approach walks the reader through each step of designing and constructing, starting with an overview of the essential working principles of valve amplifiers, the simple and complex stages, the process of linking the stages, and completing the design. The book is comprised of seven chapters all of which include a DIY guide discussion of practical aspects. The text starts with familiarization of the fundamentals of electronics, which are essential for designing and building valve amplifiers. Particular attention has been paid to providing solutions for questions that are commonly asked and faced by beginners in valve designing and construction. Valve Amplifiers is a masterful hands-on guide for both experts and novices who work with tube audio equipment, and for electronic hobbyists, audio engineers, and audiophiles. - The practical guide to analysis, modification, design, construction and maintenance of valve amplifiers - The fully up-to-date approach to valve electronics - Essential reading for audio designers and music and electronics enthusiasts alike

Autoren/Hrsg.

Jones, Morgan

Inhaltsverzeichnis

1;Front Cover;1
2;Valve Amplifiers;4
3;Copyright Page;5
4;Contents;6
5;Preface;10
6;Dedication;12
7;Acknowledgements;14
8;1. Circuit Analysis;16
8.1;Mathematical Symbols;16
8.2;Electrons and Definitions;17
8.2.1;Batteries and Lamps;19
8.2.2;Ohm’s Law;20
8.2.3;Power;21
8.2.4;Kirchhoff’s Laws;22
8.2.5;Resistors in Series and Parallel;24
8.3;Potential Dividers;29
8.3.1;Equivalent Circuits;29
8.3.2;The Thévenin Equivalent Circuit;30
8.3.3;The Norton Equivalent Circuit;33
8.3.4;Units and Multipliers;34
8.3.5;The Decibel;35
8.4;Alternating Current (AC);36
8.4.1;The Sine Wave;36
8.4.2;The Transformer;39
8.4.3;Capacitors, Inductors and Reactance;40
8.4.4;Filters;42
8.4.5;Time Constants;45
8.4.6;Resonance;46
8.4.7;RMS and Power;48
8.4.8;The Square Wave;49
8.4.9;Square Waves and Transients;50
8.4.10;Random Noise;55
8.5;Active Devices;56
8.5.1;Conventional Current Flow and Electron Flow;56
8.6;Silicon Diodes;57
8.6.1;Voltage References;58
8.7;Bipolar Junction Transistors (BJTs);60
8.7.1;The Common Emitter Amplifier;62
8.7.2;Considering DC Conditions;64
8.7.3;Input and Output Resistances;64
8.7.4;The Emitter Follower;66
8.7.5;The Darlington Pair;67
8.8;General Observations on BJTs;67
8.9;Feedback;68
8.9.1;The Feedback Equation;68
8.9.2;Practical Limitations of the Feedback Equation;69
8.9.3;Feedback Terminology and Input and Output Impedances;70
8.10;The Operational Amplifier;71
8.10.1;The Inverter and Virtual Earth Adder;72
8.10.2;The Non-Inverting Amplifier and Voltage Follower;73
8.10.3;The Integrator;75
8.10.4;The Charge Amplifier;75
8.10.5;DC Offsets;77
8.11;References;78
8.12;Recommended Further Reading;78
9;2. Basic Building Blocks;80
9.1;The Common Cathode Triode Amplifier;80
9.1.1;Limitations on Choice of the Operating Point;83
9.1.2;Conditions at the Operating Point;85
9.1.3;Dynamic, or AC, Parameters;88
9.1.4;Cathode Bias;91
9.1.5;The Effect on AC Conditions of an Unbypassed Cathode Bias Resistor;93
9.1.6;The Cathode Decoupling Capacitor;94
9.1.7;Choice of Value of Grid-Leak Resistor;96
9.1.8;Choice of Value of Output Coupling Capacitor;98
9.1.9;Miller Capacitance;98
9.1.10;Reducing Output Resistance of the Previous Stage;100
9.1.11;Guided-Grid, or Beam, Triodes;100
9.2;The Tetrode;101
9.3;The Beam Tetrode and the Pentode;102
9.3.1;The Significance of the Pentode Curves;104
9.3.2;Using the EF86 Small-Signal Pentode;106
9.4;The Cascode;109
9.5;The Charge Amplifier;117
9.6;The Cathode Follower;118
9.7;Sources and Sinks: Definitions;122
9.8;The Common Cathode Amplifier as a Constant Current Sink (CCS);124
9.8.1;Pentode Constant Current Sinks;126
9.9;The Cathode Follower with Active Load;128
9.10;The White Cathode Follower;129
9.10.1;Analysis of the Self-Contained White Cathode Follower;129
9.10.2;The White Cathode Follower as an Output Stage;132
9.11;The µ-Follower;133
9.11.1;The Importance of the AC Loadline;137
9.11.2;Upper Valve Choice in the µ-Follower;137
9.11.3;Limitations of the µ-Follower;138
9.12;The Shunt-Regulated Push–Pull Amplifier (SRPP);140
9.13;The ß-Follower;143
9.14;The Cathode-Coupled Amplifier;145
9.15;The Differential Pair;148
9.15.1;Gain of the Differential Pair;150
9.15.2;Output Resistance of the Differential Pair;150
9.15.3;AC Balance of the Differential Pair and Signal at the Cathode Junction;151
9.15.4;Common-Mode Rejection Ratio (CMRR);151
9.15.5;Power Supply Rejection Ratio (PSRR);153
9.16;Semiconductor Constant Current Sinks;154
9.16.1;Using Transistors as Active Loads for Valves;157
9.16.2;Optimising rout by Choice of Transistor Type;160
9.16.3;Field-Effect Transistors (FETs) as Constant Current Sinks;162
9.16.4;Designing Constant Current Sinks Using the DN2540N5;164
9.17;References;168
9.18;Recommended Further Reading;169
10;3. Dynamic Range: Distortion and Noise;170
10.1;Distortion;170
10.1.1;Defining Distortion;170
10.1.2;Measuring Non-Linear Distortion;171
10.1.3;Distortion Measurement and Interpretation;172
10.1.4;Choosing the Measurement;173
10.1.5;Refining Harmonic Distortion Measurement;174
10.1.6;Weighting of Harmonics;174
10.1.7;Summation and Rectifiers;175
10.1.8;Alternative Rectifiers;177
10.1.9;Noise and THD+N;177
10.1.10;Spectrum Analysers;178
10.2;Digital Concepts;178
10.2.1;Sampling;179
10.2.2;Scaling;179
10.2.3;Quantisation;180
10.2.4;Number Systems;180
10.2.5;Precision;180
10.3;The Fast Fourier Transform (FFT);181
10.3.1;The Periodicity Assumption;182
10.3.2;Windowing;182
10.3.3;How the Author’s Distortion Measurements Were Made;183
10.4;Designing for Low Distortion;184
10.5;Signal Amplitude;184
10.5.1;Cascodes and Distortion;187
10.6;Grid Current;188
10.6.1;Distortion due to Grid Current at Contact Potential;188
10.6.2;Distortion due to Grid Current and Volume Controls;189
10.6.3;Operating with Grid Current (Class A2);190
10.7;Distortion Reduction by Parameter Restriction;192
10.8;Distortion Reduction by Cancellation;195
10.8.1;Differential Pair Distortion Cancellation;197
10.8.2;Push–Pull Distortion Cancellation;199
10.8.3;The Western Electric Harmonic Equaliser;199
10.8.4;Side-Effects of the Harmonic Equaliser;201
10.9;DC Bias Problems;203
10.9.1;Cathode Resistor Bias;203
10.9.2;Grid Bias (Rk=0);205
10.9.3;Rechargeable Battery Cathode Bias (rk=0);206
10.9.4;Diode Cathode Bias (rk˜0);206
10.9.5;Constant Current Sink Bias;210
10.10;Individual Valve Choice;211
10.10.1;Which Valves Were Explicitly Designed to be Low Distortion?;211
10.10.2;Carbonising of Envelopes;213
10.10.3;Deflecting Electrons;213
10.10.4;Testing to Find Low-Distortion Valves;214
10.10.5;The Test Circuit;214
10.10.6;Audio Test Level and Frequency;215
10.10.7;Test Results;215
10.10.8;Interpretation;218
10.10.9;A Convention;220
10.10.10;Alternative Medium-µ Valves;220
10.10.11;Weighted-Distortion Results;221
10.10.12;Overall Conclusions;221
10.11;Coupling from One Stage to the Next;222
10.11.1;Blocking;223
10.11.2;Transformer Coupling;225
10.11.3;Low Frequency Step Networks;225
10.11.4;Level Shifting and DC Coupling;226
10.11.5;A DC Coupled Class A Electromagnetic Headphone Amplifier;228
10.11.6;Using a Norton Level Shifter;231
10.12;Distortion and Negative Feedback;234
10.13;Carbon Resistors and Distortion;237
10.14;Noise;237
10.15;Noise from Resistances;238
10.15.1;Noise from Resistive Volume Controls;238
10.16;Noise from Amplifying Devices;239
10.16.1;Grid Current Noise and the Poisson Distribution;241
10.16.2;Electrometers and Grid Current;241
10.17;Noise in DC References;245
10.17.1;How the Author’s DC Reference Noise Measurements Were Made;245
10.17.2;Gas Reference Noise Measurements;247
10.17.3;Variation of Gas Reference Noise with Operating Current;247
10.17.4;Semiconductor Reference Noise Measurements and Statistical Summation;247
10.17.5;Variation of Zener Reference Noise with Operating Current;249
10.17.6;Noise of the Composite Zener Compared to a 317;250
10.17.7;Red LED Noise;251
10.18;References;251
10.19;Recommended Further Reading;252
11;4. Component Technology;254
11.1;Resistors;254
11.1.1;Preferred Values;254
11.1.2;Heat;255
11.1.3;Metal Film Resistors;256
11.1.4;Power (Wirewound) Resistors;259
11.1.5;Ageing Wirewound Resistors;259
11.1.6;Noise and Inductance of Wirewound Resistors;260
11.1.7;Non-Inductive Thick Film Power Resistors;263
11.2;General Considerations on Choosing Resistors;263
11.2.1;Tolerance;263
11.2.2;Heat;263
11.2.3;Voltage Rating;264
11.2.4;Power Rating;264
11.3;Capacitors;264
11.3.1;The Parallel Plate Capacitor;264
11.3.2;Reducing the Gap Between the Plates and Adding Plates;265
11.3.3;The Dielectric;265
11.4;Different Types of Capacitors;266
11.4.1;Air Dielectric, Metal Plate (er˜1);268
11.4.2;Plastic Film, Foil Plate Capacitors (211.4.3;Metallised Plastic Film Capacitors;271
11.4.4;Metallised Paper Capacitors (1.811.4.5;Silvered Mica Capacitors (Muscovite Mica, er=7.0);272
11.4.6;Ceramic Capacitors;272
11.4.7;Electrolytic Capacitors;273
11.4.8;Aluminium Electrolytic Capacitors (er˜8.5);273
11.4.9;Tantalum Electrolytic Capacitors (er˜25);281
11.4.10;Variation of Capacitance with Frequency;282
11.4.11;Imaginary Capacitance;282
11.5;General Considerations in Choosing Capacitors;284
11.5.1;Voltage Rating;284
11.5.2;Capacitance Value;284
11.5.3;Heat;285
11.5.4;ESR;285
11.5.5;Leakage and ‘d’;285
11.5.6;Microphony;285
11.5.7;Bypassing;286
11.6;Magnetic Components;287
11.7;Inductors;288
11.7.1;Air-Cored Inductors;288
11.7.2;Gapped Cores for AC Only;290
11.7.3;Gapped Cores for AC and DC (Power Supply Chokes);291
11.7.4;Self-Capacitance;292
11.8;Transformers;294
11.8.1;Iron Losses;294
11.8.2;DC Magnetisation;298
11.8.3;Copper Losses;299
11.8.4;Electrostatic Screens;299
11.8.5;Magnetostriction;300
11.8.6;Output Transformers, Feedback and Loudspeakers;300
11.8.7;Transformer Models;301
11.8.8;Input Transformer Loading;304
11.9;Why Should I Use a Transformer?;306
11.10;General Considerations in Choosing Transformers;307
11.11;Uses and Abuses of Audio Transformers;308
11.11.1;Guitar Amplifiers and Arcs;308
11.11.2;Other Modes of Destruction;309
11.11.3;Magnetic Screening Cans;309
11.11.4;Magnetic Core Deterioration;309
11.12;Thermionic Valves;310
11.12.1;History;310
11.12.2;Emission;311
11.12.3;Electron Velocity;312
11.12.4;Transit Time;313
11.13;Individual Elements of the Valve Structure;314
11.13.1;The Cathode;314
11.14;Thoriated Tungsten Filament Fragility;317
11.14.1;Direct Versus Indirectly Heated Cathodes;318
11.14.1.1;The Thermal Problem;318
11.14.1.2;The Electrostatic Problem;319
11.14.1.3;The Electromagnetic Problem;319
11.14.1.4;The Indirectly Heated Cathode Solution;319
11.14.2;Heater/Cathode Insulation;320
11.14.3;Cathode Temperature Considerations;322
11.14.4;Heaters and their Supplies;322
11.14.5;Current Hogging and Heater Power;324
11.14.6;Heater Voltage and Current;326
11.14.7;The Control Grid;329
11.14.8;Grid Current;330
11.14.9;Thermal Runaway due to Grid Current;330
11.14.10;Grid Emission;330
11.14.11;Frame-Grid Valves;331
11.14.12;Variable-µ Grids and Distortion;332
11.14.13;Other Grids;333
11.14.14;The Anode;334
11.14.15;The Vacuum and Ionisation Noise;337
11.14.16;The Getter;338
11.14.17;The Mica Wafers and Envelope Temperature;339
11.14.18;Valve Sockets – Losses and Noise;341
11.14.19;Valve Bases and the Loktal™ Base;341
11.14.20;The Glass Envelope and the Pins;343
11.14.21;PCB Materials;344
11.15;References;345
11.16;Recommended Further Reading;346
12;5. Power Supplies;348
12.1;The Major Blocks;348
12.2;Rectification and Smoothing;349
12.2.1;Choice of Rectifiers/Diodes;349
12.2.2;Rectifiers To Be Avoided (Gas);355
12.2.3;Rectifiers To Be Avoided (Selenium);357
12.2.4;Rectifiers To Be Avoided (Copper Oxide);357
12.2.5;RF Interference/Spikes;358
12.2.6;The Single Reservoir Capacitor Approach;358
12.2.7;Ripple Voltage;359
12.2.8;The Effect of Ripple Voltage on Output Voltage;360
12.2.9;Ripple Current and Conduction Angle;361
12.2.10;Transformer Core Saturation;365
12.2.11;Choosing the Reservoir Capacitor and Transformer;365
12.2.12;Back-to-Back Mains Transformers for HT Supplies;368
12.2.13;Voltage Multipliers;370
12.2.14;The Choke Input Power Supply;372
12.2.15;Minimum Load Current for a Choke Input Supply;373
12.2.16;Current Rating of the Choke;374
12.2.17;Mains Transformer Current Rating for a Choke Input Supply;376
12.2.18;Current Spikes and Snubbers;376
12.2.19;Intermediate Mode: The Region Between Choke Input and Capacitor Input;380
12.2.20;PSUD2;382
12.2.21;Broadband Response of Practical LC Filters;384
12.2.21.1;Region 1;384
12.2.21.2;Region 2;386
12.2.21.3;Region 3;386
12.2.21.4;Region 4;386
12.2.22;Estimation of Wide-Band LC Response;390
12.2.23;Sectioned RC Filters;391
12.3;Regulators;393
12.3.1;The Fundamental Series Regulator;394
12.3.2;The Two-Transistor Series Regulator;396
12.3.3;The Speed-Up Capacitor;397
12.3.4;Compensating for Regulator Output Inductance;399
12.3.5;A Variable Bias Voltage Regulator;399
12.3.6;The 317 IC Voltage Regulator;401
12.3.7;The 317 as an HT Regulator;403
12.3.8;Valve Voltage Regulators;405
12.3.9;Optimised Valve Voltage Regulators;408
12.3.10;Using a Pentode’s g2 as an Input for Hum Cancellation;409
12.3.11;Increasing Output Current Cheaply;409
12.3.12;Regulator Sound;412
12.3.13;Power Supply Output Resistance and Stereo Crosstalk;412
12.3.14;Power Supply Output Resistance and Amplifier Stability;413
12.3.15;The Statistical Regulator;414
12.3.16;Bypassing the Composite Zener;417
12.3.17;Optimising the Statistical Regulator;419
12.3.18;References for Elevated Heater Supplies – the THINGY;420
12.4;Common-Mode Interference;423
12.4.1;Heaters and History;423
12.4.2;How Common-Mode Heater Interference Enters the Audio Signal;424
12.4.3;Mains Transformers and Inter-Winding Capacitance;424
12.4.4;Reducing Transformer Inter-Winding Capacitance;425
12.4.5;Post-Transformer Filtering;426
12.5;Practical Issues;427
12.5.1;Transformer Regulation;427
12.5.2;HT Capacitors and Voltage Ratings;428
12.5.3;Can Potentials and Undischarged HT Capacitors;429
12.5.4;The Switch-On Surge;430
12.5.5;Mains Fusing;430
12.5.6;Mains Switching;431
12.6;A Practical Design;432
12.6.1;HT Regulation;433
12.6.2;HT Rectification and Smoothing (a PSUD2 Exercise);435
12.6.3;Heater Rectification and Smoothing (a Manual Exercise);438
12.6.4;Heater Regulation;439
12.6.5;Mains Filtering;440
12.7;Adapting the Power Supply to the EC8010 RIAA Stage;441
12.7.1;HT Regulation;443
12.7.2;Reference Voltages;444
12.7.3;HT Rectification and Smoothing (a PSUD2 Exercise);444
12.7.4;Heater Regulation;446
12.7.5;Heater Rectification and Smoothing (a Manual Exercise);447
12.8;References;448
12.9;Recommended Further Reading;449
13;6. The Power Amplifier;450
13.1;The Output Stage;450
13.1.1;The Single-Ended Class A Output Stage;451
13.1.2;The Significance of High Output Resistance;453
13.1.3;Transformer Imperfections;454
13.2;Classes of Amplifiers;456
13.2.1;Class A;456
13.2.2;Class B;456
13.2.3;Class C;456
13.2.4;Class *1;458
13.2.5;Class *2;458
13.3;The Push–Pull Output Stage and the Output Transformer;458
13.3.1;Modifying the Connection of the Output Transformer;461
13.4;Output Transformer-Less (OTL) Amplifiers;465
13.5;The Entire Amplifier;465
13.6;The Driver Stage;467
13.7;The Phase Splitter;469
13.7.1;The Differential Pair and Its Derivatives;470
13.8;The Input Stage;479
13.9;Stability;480
13.9.1;Slugging the Dominant Pole;480
13.9.2;Low Frequency Instability, or Motorboating;482
13.9.3;Parasitic Oscillation and Control Grid-Stoppers;483
13.9.4;Parasitic Oscillation of Ultra-Linear Output Stages, and g2 Stoppers;484
13.9.5;Parasitic Oscillation and Anode Stoppers;484
13.9.6;High Frequency Stability and the 0V Chassis Bond;484
13.9.7;Stability Margin;484
13.10;Classic Power Amplifiers;485
13.10.1;The Williamson;485
13.10.2;The Mullard 5-20;487
13.10.3;The Quad II;492
13.11;New Designs;495
13.12;Single-Ended Madness;495
13.13;The Scrapbox Challenge Single-Ended Amplifier;495
13.13.1;Choice of Output Valve;496
13.13.2;Choice of Output Class;497
13.13.3;Choosing the DC Operating Point by Considering Output Power and Distortion;497
13.13.4;Specifying the Output Transformer;498
13.13.5;Biassing the Valve;498
13.13.6;The Cathode Bypass Capacitor;499
13.13.7;Finding the Required HT Voltage;500
13.13.8;HT Smoothing;500
13.13.9;HT Rectification;500
13.13.10;The HT Transformer;501
13.13.11;HT Choke Suitability;502
13.13.12;The HT Regulator Option;503
13.13.13;Estimating Amplifier Output Resistance;505
13.13.14;What are the Driver Stage Requirements?;506
13.13.15;Driver Stage Topology;506
13.13.16;Choice of Valve for the Driver Stage;507
13.13.17;Determining the Driver Stage Operating Point;507
13.13.18;Setting Driver Stage Bias;508
13.13.19;Is the Output Resistance and Gain of the Proposed Driver Stage Adequate?;508
13.13.20;But What About Global Feedback?;509
13.13.21;Summing Up;509
13.13.22;Teething Problems;509
13.13.23;Listening Tests;512
13.13.24;Designer’s Observations;512
13.13.25;Conclusions;513
13.14;Obtaining more than Single Digit Output Power;515
13.14.1;Sex, Lies and Output Power;515
13.14.2;Loudspeaker Efficiency and Power Compression;516
13.14.3;Active Crossovers and Zobel Networks;516
13.14.4;Parallel Output Valves and Transformer Design;518
13.15;Driving Higher Power Output Stages;519
13.16;The Crystal Palace Amplifier;520
13.16.1;13E1 Conditions;522
13.16.2;Driver Requirements;525
13.16.3;Finding a Topology that Satisfies the Driver Requirements;525
13.16.3.1;(1) Minimal Measured Distortion;525
13.16.3.2;(2) Distortion to be Composed of Low Order Harmonics;525
13.16.3.3;(3) Push–pull Output with Good Balance;525
13.16.3.4;(4) Large Undistorted Voltage Swing;526
13.16.3.5;(5) Sufficient Gain to Enable Global Negative Feedback if Required;526
13.16.3.6;(6) Low DC Output Resistance to Avoid Problems with DC Grid Current;526
13.16.3.7;(7) Low AC Output Resistance to Drive Load Capacitance;526
13.16.3.8;(8) Tolerance of Output Stage Conduction Angle Changes from 360° to 0°;526
13.16.3.9;(9) Instantaneous Recovery Even After Gross Overload;527
13.16.4;Circuit Topology: Power Supplies and Their Effect on Constant Current Sinks;527
13.16.5;Va(max) and the Positive HT Supply;528
13.16.6;Symmetry and the Negative HT Supply;529
13.16.7;The Second Differential Pair and Output Stage Current;529
13.16.8;Why Not Have Tighter Stabilisation?;530
13.16.9;The First Differential Pair, Its HT Supply, and Linearity;532
13.16.10;Valve Matching;532
13.16.11;The Essential Twiddly Bits;533
13.16.12;The Cascode Constant Current Sink and Stabilisation Against Mains Variation;533
13.16.13;The 334Z Constant Current Sink and Thermal Stability;536
13.16.14;High Frequency Stability;537
13.16.15;HT Regulators;537
13.16.16;Stereo versus Mass;539
13.16.17;Power Supply Design;539
13.16.18;Designer’s Observations;540
13.16.19;Exceeding Vg2;540
13.16.20;GM70;542
13.16.21;Measuring Ik;542
13.16.22;Global Negative Feedback;542
13.16.23;Conclusions;546
13.17;The Bulwer-Lytton Scalable Parallel Push–Pull Amplifier;546
13.17.1;Background;546
13.17.2;Designing the Followers to Drive the Output Valves;548
13.17.3;Comparing Cathode and FET Source Followers;548
13.17.4;Output Stage Bias, Balance and Coupling;551
13.17.5;Providing Gain;554
13.17.6;Gain Stage CCS and Gain Balance;554
13.17.7;Balanced Inputs on Power Amplifiers;555
13.17.8;The Volume Control and Baffle Step Compensation;556
13.17.9;Audio Circuit Comments;557
13.17.10;Power Supplies;558
13.17.11;Global Negative Feedback;560
13.18;References;560
13.19;Further reading;561
14;7. The Pre-Amplifier;562
14.1;Input Selection;563
14.1.1;Disparate Levels between Sources;563
14.1.2;Adjacent Contact Capacitance (Crosstalk Between Sources);564
14.1.3;Contact and Leakage Resistance (Noise);565
14.1.4;Solutions and Problems Peculiar to Electromechanical Switches (Relays);565
14.2;Volume Control;566
14.2.1;Limitations on the Control’s Value (Disturbing Frequency Response);567
14.2.2;Logarithmic Law (Perceived Volume Not Changing Smoothly with Rotation);568
14.2.3;Switched Attenuators (Disturbing Channel Matching);569
14.2.4;Switched Attenuator Design;570
14.2.5;Spreadsheets and Volume Controls;573
14.2.6;Volume Controls for Digital Active Crossovers;574
14.2.7;Volume Control Values and Their Effect on Noise;577
14.2.8;Grid-Leak Resistors and Volume Controls;578
14.2.9;Balanced Volume Controls;580
14.2.10;Light-Sensitive Resistors as Volume Controls;580
14.2.11;Transformer Volume Controls;582
14.3;Balance Control;583
14.3.1;Law Faking;583
14.4;Cable Driver;587
14.4.1;Determination of Required Quiescent Current;587
14.4.2;Choice of Follower Valve;589
14.4.3;Practical Considerations;590
14.4.4;Adding Gain;592
14.4.5;Polarity Inversion;593
14.5;Tone Control;594
14.6;Obtaining a Clean Signal from Analogue Disc;600
14.6.1;Comparison of Analogue Levels between Vinyl and Digital Sources;600
14.6.2;RIAA and Replay Rumble;601
14.6.3;The Mechanical Problem;602
14.6.4;Arm Wiring and Moving Coil Cartridge DC Resistance;603
14.6.5;Hum Loops and Unbalanced Interfaces;604
14.6.6;Balanced Working and Pick-Up Arm Wiring;604
14.7;RIAA Stage Design;606
14.7.1;Determination of Requirements;607
14.7.2;Implementing RIAA Equalisation;609
14.7.3;‘All in One Go’ Equalisation;611
14.7.4;Split RIAA Equalisation;612
14.7.5;The Final Choice;614
14.8;A Simplified Example RIAA Stage;614
14.8.1;Noise and Input Capacitance of the Input Stage;614
14.8.2;Valve Noise;620
14.8.3;1/f Noise;621
14.8.4;Connecting Devices in Parallel to Reduce noise;621
14.8.5;Valve Noise Summary;622
14.8.6;Noise Advantage due to RIAA Equalisation;622
14.8.7;Stray Capacitances;623
14.8.8;Calculation of Component Values for 75µs;623
14.8.9;180µs, 318µs Equalisation and the Problem of Interaction;625
14.9;3180µs and 318µs Equalisation;626
14.9.1;Awkward Values and Tolerances;627
14.10;The EC8010 RIAA Stage;629
14.10.1;The Input Stage;629
14.10.2;Optimising the Input Transformer;632
14.10.3;The Second Stage;633
14.10.4;The Output Stage;634
14.10.5;Refining Valve Choice by Heaters;634
14.10.6;Choosing the Implementation of RIAA Equalisation;635
14.10.7;Grid Current Distortion and RIAA Equaliser Series Resistances;635
14.10.8;3180µs, 318µs Pairing Errors due to Miller Capacitance;636
14.10.9;The 75µs Problem;636
14.10.10;The Computer Aided Design (CAD) Solution;637
14.10.11;3180µs, 318µs Pairing Manipulation;637
14.10.12;75µs/3.18µs Manipulation;638
14.10.13;Practical RIAA Considerations;639
14.10.14;RIAA Direct Measurement Problems;639
14.10.15;Production Tolerances and Component Selection;642
14.10.16;RIAA Equalisation Errors due to Valve Tolerances;643
14.11;The Balanced Hybrid RIAA Stage;643
14.11.1;No Step-Up Transformers;644
14.11.2;Semiconductors to the Rescue;644
14.11.3;Miller Capacitance;645
14.11.4;DC Stabilisation and Consequent Gain Reduction;646
14.11.5;JFET Noise;646
14.11.6;BJT Noise;647
14.11.7;Choosing between the BJT and JFET: Equalisation, Distortion and HT Power;648
14.11.8;Reconciling the Balanced Decision with Practicalities;649
14.11.9;Implications of the Block Diagram;649
14.11.10;The Unity-Gain Cable Drivers;650
14.11.11;Deciding the HT Voltage;651
14.11.12;Input Stage BJT Miller Capacitance;652
14.11.13;VCE and BJT Linearity;653
14.11.14;Input Resistance and Bias Current;654
14.11.15;Input Stage Noise;655
14.11.16;RIAA Calculations;656
14.11.17;The Source Followers;657
14.11.18;The Constant Current Sinks;658
14.11.19;The HT Supply;658
14.11.20;Total Gain and Channel Balance;660
14.11.21;Summary;660
14.12;References;661
14.13;Recommended Further Reading;661
15;Appendix;662
15.1;Valve Data;662
15.2;Standard Component Values;666
15.3;Resistor Colour Code;666
15.4;Plastic Capacitor Coding;668
15.5;Cable;668
15.6;Square Wave Sag and Low Frequency f–3 dB;669
15.7;Playing 78s;671
15.8;Equalisation;672
15.9;CD;674
15.10;Sourcing Components: Bargains and Dealing Directly;675
15.11;References;677
16;Index;678

Leseproben

Chapter 1 Circuit Analysis
Publisher Summary
This chapter illustrates Circuit Analysis. Electrons are charged particles. Charged objects are attracted to other charged particles or objects. Charged objects come in two forms—negative and positive. Unlike charges attract, and like charges repel. Electrons are negative and positrons are positive, but while electrons are stable in the universe, positrons encounter an electron almost immediately after production, resulting in mutual annihilation and a pair of 511 keV gamma rays. An electron is very small, and does not have much of a charge, so one needs a more practical unit for defining charge. That practical unit is the coulomb (C). One could say that 1 C of charge had flowed between one point and another, which would be equivalent to saying that approximately 6,240,000,000,000,000,000 electrons had passed, but much handier. Simply being able to say that a large number of electrons had flowed past a given point is not in it very helpful. One might say that a billion cars have traveled down a particular section of motorway since it was built, but if he/she were planning a journey down that motorway, he or she would want to know the flow of cars per hour through that section. In order to look at the interesting business of designing and building valve amplifiers, we need some knowledge of electronics funmentals. Unfortunately, fundamentals are not terribly interesting, and to cover them fully would consume the entire book. Ruthless pruning is, therefore, necessary to condense what is needed in one chapter. It is thus with deep sorrow that the author has had to forsaken complex numbers and vectors, whilst the omission of differential calculus is a particularly poignant loss. All that is left is ordinary algebra, and although there are lots of equations, they are timid, miserable creatures and quite defenceless. If you are comfortable with basic electronic terms and techniques, then please feel free to go directly to Chapter 2, where valves appear. Mathematical Symbols
Unavoidably, a number of mathematical symbols are used, some of which you may have forgotten, or perhaps not previously met: a=b a is totally equivalent to b a=b a equals b a˜b a is approximately equal to b a?b a is proportional to b a?b a is not equal to b a>b a is greater than b aElectrons are charged particles. Charged objects are attracted to other charged particles or objects. A practical demonstration of this is to take a balloon, rub it briskly against a jumper and then place the rubbed face against a wall. Let it go. The balloon remains stuck to the wall. This is because we have charged the balloon, and so there is an attractive force between it and the wall. (Although the wall was initially uncharged, placing the balloon on the wall induced a charge.) Charged objects come in two forms: negative and positive. Unlike charges attract, and like charges repel. Electrons are negative and positrons are positive, but whilst electrons are stable in our universe, positrons encounter an electron almost immediately after production, resulting in mutual annihilation and a pair of 511 keV gamma rays. If we don’t have ready access to positrons, how can we have a positively charged object? Suppose we had an object that was negatively charged, because it had 2,000 electrons clustered on its surface. If we had another, similar, object that only had 1,000 electrons on its surface, then we would say that the first object was more negatively charged than the second, but as we can’t count how many electrons we have, we might just as easily have said that the second object was more positively charged than the first. It’s just a matter of which way you look at it. To charge our balloon, we had to do some work and use energy. We had to overcome friction when rubbing the balloon against the woollen jumper. In the process, electrons were moved from one surface to the other. Therefore, one object (the balloon) has acquired an excess of electrons and is negatively charged, whilst the other object (woollen jumper) has lost the same number of electrons and is positively charged. The balloon would, therefore, stick to the jumper. Or would it? Certainly it will be attracted to the jumper, but what happens when we place the two in contact? The balloon does not stick. This is because the fibres of the jumper were able to touch the whole of the charged area on the balloon, and the electrons were so attracted to the jumper that they moved back onto the jumper, thus neutralising the charge. At this point, we can discard vague talk of balloons and jumpers because we have just observed electron flow. An electron is very small, and doesn’t have much of a charge, so we need a more practical unit for defining charge. That practical unit is the coulomb (C). We could now say that 1 C of charge had flowed between one point and another, which would be equivalent to saying that approximately 6,240,000,000,000,000,000 electrons had passed, but much handier. Simply being able to say that a large number of electrons had flowed past a given point is not in itself very helpful. We might say that a billion cars have travelled down a particular section of motorway since it was built, but if you were planning a journey down that motorway, you would want to know the flow of cars per hour through that section. Similarly in electronics, we are not concerned with the total flow of electrons since the dawn of time, but we do want to know about electron flow at any given instant. Thus, we could define the flow as the number of coulombs of charge that flowed past a point in one second. This is still rather long-winded, and we will abbreviate yet further. We will call the flow of electrons current, and as the coulomb/second is unwieldy, it will be redefined as a new unit, the ampere (A). Because the ampere is such a useful unit, the definition linking current and charge is usually stated in the following form. One coulomb is the charge moved by one ampere flowing for one second. (coulombs)=current(amperes)×time(seconds) This is still rather unwieldy, so symbols are assigned to the various units: charge has symbol Q, current I and time t. =It This is a very useful equation, and we will meet it again when we look at capacitors (which store charge). Meanwhile, current has been flowing, but why did it flow? If we are going to move electrons from one place to another, we need a force to cause this movement. This force is known as the electro motive force (EMF). Current continues to flow whilst this force is applied, and it flows from a higher potential to a lower potential. If two points are at the same potential, no current can flow between them. What is important is the potential difference (pd). A potential difference causes a current to flow between two points. As this is a new property, we need a unit, a symbol and a definition to describe it. We mentioned work being done in charging the balloon, and in its very precise and physical sense, this is how we can define potential difference, but first, we must define work. One joule of work is done if a force of one newton moves one metre from its point of application. This very physical interpretation of work can be understood easily once we realise that it means that one joule of work would be done by moving one kilogramme a distance of one metre in one second. Since charge is directly related to the mass of electrons moved, the physical definition of work can be modified to define the force that causes the movement of charge. Unsurprisingly, because it causes...