book

Small Signal Audio Design, 3rd Edition

by Douglas Self

April 2020

Intermediate to advanced

784 pages

24h 4m

English

Focal Press

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SignalsAmplifiersVoltage AmplifiersTransconductance AmplifiersCurrent AmplifiersTransimpedance AmplifiersNegative FeedbackNominal Signal Levels and Dynamic RangeFrequency ResponseFrequency Response: Cascaded StagesPhase PerceptionGain StructuresAmplification Then AttenuationAttenuation Then AmplificationRaising the Input Signal to the Nominal LevelActive Gain ControlsNoiseJohnson NoiseShot Noise1/f Noise (Flicker Noise)Popcorn NoiseSumming Noise SourcesNoise in AmplifiersNoise in Bipolar TransistorsBipolar Transistor Voltage NoiseBipolar Transistor Current NoiseNoise in JFETsNoise in OpampsNoise GainLow-Noise Opamp CircuitryNoise MeasurementsHow to Attenuate QuietlyHow to Amplify QuietlyHow to Invert QuietlyHow to Balance QuietlyUltra-Low-Noise Design With Multi-Path AmplifiersUltra-Low-Noise Voltage BuffersUltra-Low-Noise AmplifiersMultiple Amplifiers for Greater Drive Capability
ConductorsCopper and Other Conductive ElementsThe Metallurgy of CopperGold and Its UsesCable and Wiring ResistancePCB Track ResistancePCB Track-to-Track CrosstalkThe Three-Layer PCBImpedances and Crosstalk: A Case HistoryResistorsThrough-Hole ResistorsSurface-Mount ResistorsResistor SeriesResistor Accuracy: Two-Resistor CombinationsResistor Accuracy: Three-Resistor CombinationsOther Resistor CombinationsResistor Value DistributionsThe Uniform DistributionResistor ImperfectionsResistor Excess NoiseResistor Non-LinearityCapacitorsCapacitor SeriesCapacitor Non-Linearity ExaminedNon-Electrolytic Capacitor Non-LinearityElectrolytic Capacitor Non-LinearityInductors

Why Use Discrete Transistor Circuitry?Bipolars and FETsBipolar Junction TransistorsThe Transistor EquationBetaUnity-Gain Buffer StagesThe Simple Emitter-FollowerThe Constant-Current Emitter-FollowerThe Push-Pull Emitter-FollowerEmitter-Follower StabilityCFP Emitter-FollowersImproved Unity-Gain BuffersGain StagesOne-Transistor Shunt-Feedback Gain StagesOne-Transistor Series-Feedback Gain StagesTwo-Transistor Shunt-Feedback Gain StagesTwo-Transistor Shunt-Feedback Stages: Improving LinearityTwo-Transistor Shunt-Feedback Stages: NoiseTwo-Transistor Shunt-Feedback Stages: BootstrappingTwo-Transistor Shunt-Feedback Stages as Summing AmplifiersTwo-Transistor Series-Feedback Gain StagesDiscrete Opamp DesignDiscrete Opamp Design: The Input StageDiscrete Opamp Design: The Second StageDiscrete Opamp Design: The Output StageHigh-Input-Impedance Bipolar Stages
IntroductionA Very Brief History of OpampsOpamp Properties: NoiseOpamp Properties: Slew RateOpamp Properties: Common Mode RangeOpamp Properties: Input Offset VoltageOpamp Properties: Bias CurrentOpamp Properties: CostOpamp Properties: DistortionOpamp Internal DistortionSlew-Rate Limiting DistortionDistortion Due to LoadingThermal DistortionCommon-Mode DistortionCommon-Mode Distortion: Bipolar Input OpampsCommon-Mode Distortion: JFET OpampsSelecting the Right OpampOpamps Surveyed: BJT Input TypesThe LM741 OpampThe NE5532/5534 OpampDeconstructing the 5532The LM4562 OpampThe AD797 OpampThe OP27 OpampThe OP270 OpampThe OP275 OpampOpamps Surveyed: JFET Input TypesThe TL072 OpampThe TL052 OpampThe OPA2134 OpampThe OPA604 OpampThe OPA627 Opamp
High Fidelity From Low VoltagesRunning Opamps From a Single +5 V Supply RailOpamps for 5 V OperationThe NE5532 in +5 V OperationThe LM4562 in +5 V OperationThe AD8022 in +5 V OperationThe AD8397 in +5 V OperationOpamps for 3.3 V Single-Rail Operation
IntroductionPassive FiltersActive FiltersLow-Pass FiltersHigh-Pass FiltersCombined Low-Pass and High-Pass FiltersBand-Pass FiltersNotch FiltersAll-Pass FiltersFilter CharacteristicsSallen and Key Low-Pass FiltersSallen and Key High-Pass FiltersDistortion in Sallen and Key FiltersMultiple-Feedback Band-Pass FiltersNotch FiltersDifferential Filters
Passive PreamplifiersActive PreamplifiersAmplification and the Gain-Distribution ProblemActive Gain ControlsActive Gain Controls Plus Passive AttenuatorsRecording FacilitiesTone Controls
Amplifier Stages With Gain From Unity Upwards: Single-Gain PotAmplifier Stages With Gain From Unity Upwards: Dual-Gain PotCombining Gain Stages With Active FiltersAmplifier Stages With Gain From Zero Upwards: Single-Gain PotAmplifier Stages With Gain From Zero Upwards: Dual-Gain PotSwitched-Gain Amplifiers
Cartridge TypesThe Vinyl MediumSpurious SignalsOther Vinyl ProblemsMaximum Signal Levels From VinylMoving-Magnet Cartridge SensitivitiesOverload Margins and Amplifier LimitationsEqualisation and Its DiscontentsThe Unloved IEC AmendmentThe “Neumann Pole”MM Amplifier ConfigurationsOpamp MM Input StagesCalculating the RIAA Equalisation ComponentsImplementing RIAA EqualisationImplementing the IEC AmendmentRIAA Series-Feedback Network ConfigurationsRIAA Optimisation: C1 as a Single E6 Capacitor, 2xE24RIAA Optimisation: C1 as 3 x 10 nF Capacitors, 2xE24RIAA Optimisation: C1 as 4 x 10 nF Capacitors, 2xE24RIAA Optimisation: The Willmann TablesRIAA Optimisation: C1 as 3 x 10 nF Capacitors, 3xE24RIAA Optimisation: C1 as 4 x 10 nF Capacitors, 3xE24Switched-Gain MM RIAA AmplifiersSwitched-Gain MM/MC RIAA AmplifiersOpen-Loop Gain and RIAA AccuracyPassive and Semi-Passive RIAA EqualisationMM Cartridge Loading and Frequency ResponseMM Cartridge–Preamplifier InteractionMM Cartridge DC and AC CouplingNoise in MM RIAA PreamplifiersHybrid MM AmplifiersBalanced MM InputsNoise in Balanced MM InputsNoise WeightingNoise MeasurementsCartridge Load Synthesis for Lower NoiseSubsonic FiltersSubsonic Filtering: Butterworth FiltersSubsonic Filtering: Elliptical FiltersSubsonic Filtering by CancellationUltrasonic FiltersA Practical MM Amplifier #3
Moving-Coil Cartridge CharacteristicsThe Limits on MC Noise PerformanceAmplification StrategiesMoving-Coil TransformersMoving-Coil Input AmplifiersAn Effective MC Amplifier ConfigurationThe Complete CircuitPerformance
The Return of TapeA Brief History of Tape RecordingThe Basics of Tape RecordingMulti-Track RecordingTape HeadsTape ReplayTape Replay EqualisationTape Replay AmplifiersReplay Noise: CalculationReplay Noise: MeasurementsLoad SynthesisNoise Reduction SystemsDolby HX-Pro
Electric Guitar TechnologyGuitar PickupsPickup CharacteristicsGuitar WiringGuitar LeadsGuitar PreamplifiersGuitar Preamplifier Noise: CalculationsGuitar Preamplifier Noise: MeasurementsGuitar Amplifiers and Guitar EffectsGuitar Direct Injection
Volume ControlsVolume Control LawsLoaded Linear PotsDual-Action Volume ControlsTapped Volume ControlsSlide FadersActive Volume ControlsThe Baxandall Active Volume ControlThe Baxandall Volume Control LawA Practical Baxandall Active Volume StageLow-Noise Baxandall Active Volume StagesThe Baxandall Volume Control: Loading EffectsAn Improved Baxandall Active Volume Stage With Lower NoiseBaxandall Active Volume Stage Plus Passive ControlThe Overlap PenaltyPotentiometers and DCBelt-Ganged Volume ControlsMotorised PotentiometersStepped Volume ControlsSwitched Attenuator Volume ControlsRelay-Switched Volume ControlsTransformer-Tap Volume ControlsIntegrated Circuit Volume ControlsLoudness ControlsThe Newcomb and Young Loudness Control
The Ideal Balance LawBalance Controls: PassiveBalance Controls: ActiveCombining Balance Controls With Other StagesSwitched Balance ControlsMono-Stereo SwitchesWidth Controls
IntroductionPassive Tone ControlsBaxandall Tone ControlsThe Baxandall One-LF-Capacitor Tone ControlThe Baxandall Two-LF-Capacitor Tone ControlThe Baxandall Two-HF-Capacitor Tone ControlThe Baxandall Tone Control: Impedance and NoiseCombining a Baxandall Stage With an Active Balance ControlSwitched-HF-Frequency Baxandall ControlsVariable-Frequency HF EQVariable-Frequency LF EQA New Type of Switched-Frequency LF EQVariable-Frequency HF and LF EQ in One StageTilt or Tone-Balance ControlsMiddle ControlsFixed Frequency Baxandall Middle ControlsThree-Band Baxandall EQ in One StageWien Fixed Middle EQWien Fixed Middle EQ: Altering the QVariable-Frequency Middle EQSingle-Gang Variable-Frequency Middle EQSwitched-Q Variable-Frequency Wien Middle EQSwitchable Peak/Shelving LF/HF EQParametric Middle EQGraphic Equalisers
IntroductionPerformance FactorsMixer Internal LevelsMixer ArchitectureThe Split Mixing ArchitectureThe In-Line Mixing ArchitectureA Closer Look at Split-Format ModulesThe Channel Module (Split Format)Effect Return ModulesThe Group ModuleThe Master ModuleTalkback and Oscillator SystemsThe In-Line Channel Module
Microphone TypesMicrophone Preamplifier RequirementsTransformer Microphone InputsThe Simple Hybrid Microphone PreamplifierThe Balanced-Feedback Hybrid Microphone Preamplifier (BFMA)Microphone and Line Input PadsThe Padless Microphone PreamplifierCapacitor Microphone Head AmplifiersRibbon Microphone Amplifiers
External Signal LevelsInternal Signal LevelsInput Amplifier FunctionsUnbalanced InputsBalanced InterconnectionsThe Advantages of Balanced InterconnectionsThe Disadvantages of Balanced InterconnectionsBalanced Cables and InterferenceBalanced ConnectorsBalanced Signal LevelsElectronic Versus Transformer Balanced InputsCommon Mode RejectionThe Basic Electronic Balanced InputThe Basic Balanced Input and Opamp EffectsOpamp Frequency Response EffectsOpamp CMRR EffectsAmplifier Component Mismatch EffectsA Practical Balanced InputVariations on the Balanced Input StageCombined Unbalanced and Balanced InputsThe Superbal InputSwitched-Gain Balanced InputsVariable-Gain Balanced InputsCombined Line Input and Balance Control Stage With Low NoiseThe Self Variable-Gain Line InputHigh Input-Impedance Balanced InputsThe Inverting Two-Opamp InputThe Instrumentation AmplifierInstrumentation Amplifier ApplicationsThe Instrumentation Amplifier With 4x GainThe Instrumentation Amplifier at Unity GainThe Instrumentation Amplifier and Gain ControlsThe Instrumentation Amplifier and the Whitlock BootstrapTransformer Balanced InputsInput Overvoltage ProtectionLow-Noise Balanced InputsLow-Noise Balanced Inputs in ActionUltra-Low-Noise Balanced Inputs
Unbalanced OutputsZero-Impedance OutputsGround-Cancelling Outputs: BasicsGround-Cancelling Outputs: Zero-Impedance OutputGround-Cancelling Outputs: CMRRGround-Cancelling Outputs: Send Amplifier NoiseGround-Cancelling Outputs: Into a Balanced InputGround-Cancelling Outputs: HistoryBalanced Outputs: BasicsBalanced Outputs: Output ImpedanceBalanced Outputs: NoiseQuasi-Floating OutputsTransformer Balanced OutputsOutput Transformer Frequency ResponseOutput Transformer DistortionReducing Output Transformer Distortion
Driving Heavy LoadsDriving HeadphonesSpecial OpampsMultiple OpampsOpamp-Transistor Hybrid AmplifiersDiscrete Class-AB Headphone AmplifiersDiscrete Class-A Headphone AmplifiersGainMaximum OutputNoise PerformancePower ConsumptionBalanced Headphone Amplifiers
Mechanical SwitchesInput-Select Switching: MechanicalThe Virtual Contact: MechanicalRelay SwitchingElectronic SwitchingSwitching with CMOS Analogue GatesCMOS Gates in Voltage ModeCMOS Gates in Current ModeCMOS Series-Shunt Current ModeControl Voltage Feedthrough in CMOS GatesCMOS Gates at Higher VoltagesCMOS Gates at Low VoltagesCMOS Gate CostsDiscrete JFET SwitchingThe Series JFET Switch in Voltage ModeThe Shunt JFET Switch in Voltage ModeJFETs in Current ModeReducing Distortion by BiasingJFET Drive CircuitryPhysical Layout and OffnessDealing With the DC ConditionsA Soft Changeover CircuitControl Voltage Feedthrough in JFETS
Mixer Bus SystemsInput ArrangementsEqualisationInsert PointsHow to Move a Circuit BlockFadersImproving Fader OffnessPost-Fade AmplifiersDirect OutputsPanpotsPassive PanpotsThe Active PanpotLCR PanpotsRouting SystemsAuxiliary SendsGroup Module Circuit BlocksSumming Systems: Voltage SummingSumming Systems: Virtual-Earth SummingBalanced Summing SystemsGround-Cancelling Summing SystemsDistributed Summing SystemsSumming AmplifiersHybrid Summing AmplifiersBalanced Hybrid Summing AmplifiersBalancing Tracks to Reduce CrosstalkThe Multi-Function Summing AmplifierPFL SystemsPFL SummingPFL SwitchingPFL DetectionVirtual-Earth PFL DetectionAFL SystemsSolo-in-Place SystemsTalkback Microphone AmplifiersLine-Up OscillatorsThe Flash BusPower Supply ProtectionConsole Cooling and Component Lifetimes
Signal-Present IndicationPeak IndicationThe Log Law Level LED (LLLL)Distributed Peak DetectionCombined LED IndicatorsVU MetersPPMsLED Bar-Graph MeteringA More Efficient LED Bar-Graph ArchitectureVacuum Fluorescent DisplaysPlasma DisplaysLiquid Crystal Displays
Gain-Control ElementsA Brief History of Gain-Control ElementsJFETsOperational Transconductance Amplifiers (OTAs)Voltage-Controlled Amplifiers (VCAs)Compressors and LimitersAttack ArtefactsDecay ArtefactsSubtractive VCA ControlNoise GatesClippingDiode ClippingActive Clipping With TransistorsActive Clipping With Opamps1. Clipping by Clamping2. Negative-Feedback Clipping3. Feedforward ClippingNoise GeneratorsPinkening Filters
Opamp Supply Rail VoltagesDesigning a ±15 V SupplyDesigning a ±17 V SupplyUsing Variable-Voltage RegulatorsImproving Ripple PerformanceDual Supplies From a Single WindingPower Supplies for Discrete CircuitryLarger Power SuppliesMutual Shutdown CircuitryVery Large Power SuppliesMicrocontroller and Relay Supplies+48 V Phantom Power Supplies
PCB Layout ConsiderationsNominal Levels and ADCsSome Typical ADCsInterfacing With ADC InputsSome Typical DACsInterfacing With DAC OutputsInterfacing With Microcontrollers

Content preview from Small Signal Audio Design, 3rd Edition

CHAPTER 8 Variable Gain Stages

This chapter deals with amplifier stages that are required to have a variable gain, usually over a wide range of +20 dB, +30 dB, or more. It does not include volume controls, which typically only have a maximum gain of +10 dB or so and have their own chapter (Chapter 13). Nor does it include balanced microphone preamplifiers, which can have a variable gain range of 80 dB or more, and also have their own chapter (Chapter 17).

These amplifier stages are very common in audio electronics. A typical application would be a guitar amplifier input that has to cover a range of playing styles and pickup sensitivities. Another major use is in compact mixers that have only one control performing the functions of both input ...