Electronics for Guitarists (eBook)

Preface 6
Who This Book Is Written For 6
Analog Rules! 7
About the Math 7
Building the Circuits 7
Vacuum Tubes 8
Safety 8
Disclaimer 8
Contents 10
Chapter 1: Power Supplies 16
Introduction 16
A Simple Power Supply Circuit 16
The Transformer 16
The Rectifier 18
Analysis of the Rectifier 19
The Frequency Domain 20
The Filter 20
Filter Analysis: The Frequency Domain 22
Power Indicators 23
Light Emitting Diodes 23
Incandescent Lamps 25
A Basic Regulated Power Supply 26
The 78xx Voltage Regulator 26
Bipolar Power Supplies 29
Using Batteries for Bipolar Power 29
A Typical Bipolar Power Supply 30
Analysis of the Secondary and Rectifier 31
A Regulated Bipolar Power Supply 31
Basic Vacuum Tube Diode Power Supplies 32
Vacuum Tube Diodes 32
The 5AR4, 5U4-GB, and 5Y3-GT Diodes 34
A Typical Vacuum Tube Diode Power Supply 35
Final Comments 36
Summary of Equations 37
Chapter 2: Pickups, Volume and Tone Controls 39
Introduction 39
Single Coil Magnetic Pickups 39
Humbucker Pickups 42
Peak and Average Output Voltages 43
More Magnetic Pickup Analysis 44
Inductance 45
Winding Resistance 45
Winding Capacitance 45
Approximate Circuit Model for a Magnetic Pickup 46
Piezoelectric Pickups 47
Piezoelectric Pickup Analysis 48
Example Calculation: Input Resistance and Corner Frequency 50
Volume and Tone Control Circuits 51
Potentiometers 51
Potentiometer Taper 51
Transfer Function 52
Rheostats 53
Basic Guitar Tone Control Operation 53
Multiple Pickups 56
Pickup Phasing 56
Amplifier Tone Controls 58
A Basic Tone Control Circuit 58
Improved Single-Pot Tone Control 59
Baxandall Tone Control 61
Final Comments 63
Summary of Equations 63
Chapter 3: Small Signal and Low Power Amplifiers 65
Introduction 65
Gain 65
Decibels 66
Other Amplifier Parameters 67
Distortion 68
Input Resistance 68
Output Resistance 69
Bandwidth 69
Slew Rate 70
Amplifier Classifications 71
Biasing 71
Class A 72
Class B 72
Class AB 73
The Load Line 73
Class A Power Dissipation Characteristics 74
The Common Emitter Configuration 75
The Emitter Follower (Common Collector) Configuration 75
The Common Base Configuration 76
Field Effect Transistors 77
Transistor Specifications 78
Basic Transistor Amplifier Analysis 79
Voltage Divider Biased CE Amplifier 79
DC Q-Point Analysis Equations for Fig.3.13 81
Beta Independence 81
AC Analysis Equations for Fig.3.13 82
Analysis Example: Voltage-Divider Biased CE Amplifier 82
DC Q-Point Analysis 82
AC Analysis 84
Experimental Results 85
Vin=10mVp-p 86
Vin=50mVp-p 86
Vin=100mVp-p 88
Amplifying a Guitar Signal 88
Frequency Response Considerations 89
Negative Feedback 90
Local and Global Feedback 93
A JFET Common-Source Class A Amplifier 93
JFET Parameters 93
JFET Amplifier Overview 94
Piezoelectric Pickup Preamplifier 95
Increasing Voltage Gain 98
A Multiple-Stage Amplifier 98
Operational Amplifiers 101
Noninverting and Inverting Amplifier Analysis 104
Power Bandwidth 106
Single Polarity Supply Operation 107
Noninverting Amplifier 107
The Two Rules of Op Amp Analysis 108
Inverting Amplifier 108
Inside the Op Amp 109
Operational Transconductance Amplifiers 111
An OTA Analysis Example 113
Other OTA Applications 114
Current Difference Amplifiers 114
An Audio Test Oscillator 117
Final Comments 118
Summary of Equations 119
Chapter 4: Solid-State Power Amplifiers 125
Introduction 125
The Basic Push-Pull Stage 125
Class AB: Eliminating Crossover Distortion 126
Output Power Determination 127
Bipolar Power Supply Operation 128
A Complete Power Amplifier 129
Output Stage Analysis 131
Transistor Thermal Analysis 132
Parallel Connected Power Transistors 133
Adding a Tone Control 135
Amplifier Stability Issues 135
Ground Reference 136
Star Grounding 136
Motorboating 137
Decoupling Capacitors 137
The Zobel Network 137
MOSFET Output Stages 139
The VBE Multiplier 140
Final Comments 141
Summary of Equations 141
Chapter 5: Guitar Effects Circuits 143
Introduction 143
Signals and Spectra 143
Time, Period, Frequency, and Pitch 144
Sinusoids in the Time Domain 145
Waveform Shape, Symmetry and Harmonic Relationships 145
Transfer Function Symmetry and Harmonics 147
An Odd Symmetry Example 149
An Even Symmetry Example 150
An Example of Neither Even Nor Odd Symmetry 150
Intermodulation Distortion 151
Perception of Distortion: Transistors vs. Tubes 155
Overdrive Circuits 155
Transistor Overdrive Circuits 156
An Op Amp Overdrive Circuit 157
Distortion Circuits 158
Diode Clippers 158
Logarithmic Amplifiers 160
Phase Shifters 161
The All Pass Filter 163
Optocouplers 164
An Experimental Phase Shifter Circuit 165
Flanging 168
Flanging vs. Phase-Shifting 168
Bucket Brigade Devices 170
A BBD-Based Flanger 172
Clock and LFO Generation 173
Chorus Effect 173
Envelope Followers 174
Signal Envelope 174
Precision Rectifier Circuits 175
An Experimental Envelope Follower 177
String Frequency-to-Pulse Converter 178
Compression and Sustain 179
Voltage Controlled Amplifiers 181
Tremolo 183
Reverberation 183
Delay Time 184
Decay Time 185
Reverb Springs 185
A Digital Reverb 187
Modulation and Pitch Shifting 188
An Experimental Ring Modulator 191
Frequency Doubling 191
Vocoders 192
Wah-Wah Circuits 194
IGMF Bandpass Filter 195
An IGMF Design Example 197
Varying fo of the IGMF 197
Experimental IGMF Wah-Wah Circuits 198
A Gyrator-Based Wah-Wah Circuit 199
Envelope Controlled Filter 202
Effects Bypassing 202
Final Comments 203
Summary of Equations 203
Chapter 6: Vacuum Tube Amplifiers 208
Introduction 208
Vacuum Tubes Used in This Book 208
Parts Sources 209
Vacuum Tube Parameters and Data Sheets 209
General Amplifier Design Principles 213
Class A, Resistance Coupled, Common Cathode Amps 213
Cathode Feedback Biasing 214
A 12AU7 Design Example 215
DC and AC Load Lines 218
Determining RK Using Plate Curves 218
Determining RK Using Transconductance Curves 219
Grid Resistor Determination 220
Amplifier AC Performance 220
Experimental Test Results 221
Q-Point Location and Distortion 221
A 12AX7 Design Example 221
Determining RK 223
Amplifier AC Performance 223
Experimental Results 224
Cathode Followers and Phase-Splitters 224
Phase Splitter DC Bias Values 225
AC Characteristics 226
Alternative Phase Splitter Circuits 227
Transformer Coupling 228
A Sampling of Audio Output Transformers 229
Triodes vs. Pentodes 232
Class A, Transformer-Coupled Amplifiers 233
Choosing an Output Tube 235
Basic Design Goals 236
Determining RK 236
Output Transformer Selection 238
The AC Load Line 239
Interpretation of the AC Load Line 240
AC Characteristics of the Amplifier 241
Pentode Mode Operation 243
Using an EL34 Tube 243
EL34 Q-Point Determination 244
A Complete Amplifier 245
Preamplifier Tube Substitutions 248
Microphonics 248
The Power Supply 248
Amplifier Performance 250
An EL84, Class A, Transformer Coupled Amplifier 250
Q-Point Location and Determination of RK 252
Output Transformer Selection and the AC Load-Line 253
AC Characteristics of the Amplifier 255
A Complete Amplifier 257
The Power Supply 258
Push-Pull Amplifiers 258
Single-Ended Class A Distortion 260
Push-Pull Class A Distortion 260
Q-Point Location and Determination of RK 260
Output Transformer Selection and the AC Load Line 262
AC Characteristics of the Amplifier 263
Some Caveats 265
A Complete Push-Pull Amplifier 266
The Power Supply 266
An Alternative Power Supply 266
Adding a Reverb Unit 268
Reverb Design Considerations 270
Grid Biasing 272
Cathode Biasing Review 272
Grid Biasing Topology 273
Advantages and Disadvantages of Grid Biasing 273
Construction Techniques and Tips 274
Chassis Materials 274
Wiring Tips 275
Testing Tips 276
Final Comments 277
Summary of Equations 278
Appendix A:Useful Formulas and Equations 281
Ohm´s Law 281
n Series Resistances 281
n Parallel Resistances 281
Frequency and Period 281
Inductive and Capacitive Reactance (j=v-1) 281
Bipolar Transistor Relationships 282
Triode Relationships 282
JFET Relationships 282
Appendix B:Selected Tube Characteristic Curves 283
Appendix C:Basic Vacuum Tube Operating Principles 290
Diodes 290
Reverse Bias 290
Forward Bias 290
Triodes 291
Amplification Factor 292
Transconductance 293
Plate Resistance 293
Tetrodes 294
Pentodes 294
Index 296