3rd Edition

Small Signal Audio Design

By Douglas Self Copyright 2020
    784 Pages 644 B/W Illustrations
    by Focal Press

    784 Pages 644 B/W Illustrations
    by Focal Press

    Small Signal Audio Design is a highly practical handbook providing an extensive repertoire of circuits that can be assembled to make almost any type of audio system. The publication of Electronics for Vinyl has freed up space for new material, (though this book still contains a lot on moving-magnet and moving-coil electronics) and this fully revised third edition offers wholly new chapters on tape machines, guitar electronics, and variable-gain amplifiers, plus much more. A major theme is the use of inexpensive and readily available parts to obtain state-of-the-art performance for noise, distortion, crosstalk, frequency response accuracy and other parameters. Virtually every page reveals nuggets of specialized knowledge not found anywhere else. For example, you can improve the offness of a fader simply by adding a resistor in the right place- if you know the right place.

    Essential points of theory that bear on practical audio performance are lucidly and thoroughly explained, with the mathematics kept to an absolute minimum. Self’s background in design for manufacture ensures he keeps a wary eye on the cost of things.

    This book features the engaging prose style familiar to readers of his other books. You will learn why mercury-filled cables are not a good idea, the pitfalls of plating gold on copper, and what quotes from Star Trek have to do with PCB design.

    Learn how to:

      • make amplifiers with apparently impossibly low noise
      • design discrete circuitry that can handle enormous signals with vanishingly low distortion
      • use humble low-gain transistors to make an amplifier with an input impedance of more than 50 megohms
      • transform the performance of low-cost-opamps
      • build active filters with very low noise and distortion
      • make incredibly accurate volume controls
      • make a huge variety of audio equalisers
      • make magnetic cartridge preamplifiers that have noise so low it is limited by basic physics, by using load synthesis
      • sum, switch, clip, compress, and route audio signals
      • be confident that phase perception is not an issue

    This expanded and updated third edition contains extensive new material on optimising RIAA equalisation, electronics for ribbon microphones, summation of noise sources, defining system frequency response, loudness controls, and much more. Including all the crucial theory, but with minimal mathematics, Small Signal Audio Design is the must-have companion for anyone studying, researching, or working in audio engineering and audio electronics.

    Chapter 1: The Basics



    Voltage amplifiers

    Transconductance amplifiers

    Current amplifiers

    Transimpedance amplifiers

    Negative feedback

    Nominal signal levels and dynamic range

    Frequency response

    Frequency response: cascaded stages

    Phase perception

    Gain structures

    Amplification then attenuation

    Attenuation then amplification

    Raising the input signal to the nominal level



    Johnson noise

    Shot noise

    1/f noise (flicker noise)

    Popcorn noise

    Summing noise sources

    Noise in amplifiers

    Noise in bipolar transistors

    Bipolar transistor voltage noise

    Bipolar transistor current voltage

    Noise in JFETs

    Noise in opamps

    Noise gain

    Low-noise opamp circuitry

    Noise measurements

    How to attenuate quietly

    How to amplify quietly

    How to invert quietly

    How to balance quietly
    Ultra low-noise design with multipath amplifiers

    Ultra low-noise voltage buffers

    Ultra low-noise amplifiers

    Multiple amplifiers for greater drive capability




    Chapter 2: Components


    Copper and other conductive elements

    The metallurgy of copper

    Gold and its uses

    Cable and wiring resistance

    PCB track resistance

    PCB track-to-track crosstalk

    The 3-layer PCB

    Impedances and crosstalk: a case history


    Through-hole resistors

    Surface-mount resistors

    Resistor series

    Resistor accuracy: two resistor combinations

    Resistor accuracy: three resistor combinations

    Other resistor combinations

    Resistor value distributions

    The uniform distribution

    Resistor imperfections

    Resistor excess noise

    Resistor non-linearity


    Capacitor series

    Capacitor non-linearity examined

    Non-electrolytic capacitor non-linearity

    Electrolytic capacitor non-linearity


    Chapter 3: Discrete transistor circuitry

    Why use discrete transistor circuitry?

    Bipolars and FETs

    Bipolar junction transistors

    The transistor equation


    Unity-gain buffer stages

    The simple emitter-follower

    The constant-current emitter-follower

    The push-pull emitter-follower

    Emitter-follower stability

    CFP emitter-followers

    Improved unity-gain buffers

    Gain stages

    One-transistor shunt-feedback gain stages

    One-transistor series-feedback gain stages

    Two-transistor shunt-feedback gain stages

    Two-transistor shunt-feedback stages: improving linearity

    Two-transistor shunt-feedback stages: noise

    Two-transistor shunt-feedback stages: bootstrapping

    Two-transistor shunt-feedback stages as summing amplifiers

    Two-transistor series-feedback gain stages

    Discrete opamp design

    Discrete opamp design: the input stage

    Discrete opamp design: the second stage

    Discrete opamp design: the output stage

    High input impedance bipolar stages




    Chapter 4: Opamps and their properties


    A Very Brief History of Opamps.

    Opamp properties: noise

    Opamp properties: slew rate

    Opamp properties: common mode range

    Opamp properties: input offset voltage

    Opamp properties: bias current

    Opamp properties: cost

    Opamp properties: distortion

    Opamp internal distortion

    Slew-rate limiting distortion

    Distortion due to loading

    Thermal distortion

    Common-mode distortion

    Common-mode distortion: Bipolar input opamps

    Common-mode distortion: JFET opamps

    Selecting The Right Opamp

    Opamps surveyed: BJT input types

    The LM741 opamp

    The NE5532/5534 opamp

    Deconstructing the 5532

    The LM4562 opamp

    The AD797 opamp

    The OP27 opamp

    The OP270 opamp

    The OP275 opamp

    Opamps surveyed: JFET input types

    The TL072 opamp

    The TL052 opamp

    The OPA2134 opamp

    The OPA604 opamp

    The OPA627 opamp



    Chapter 5: Opamps for low voltages

    High Fidelity from Low Voltages

    Running opamps from a single +5V supply rail

    Opamps for 5V operation

    The NE5532 in +5V operation

    The LM4562 in +5V operation

    The AD8022 in +5V operation

    The AD8397 in +5V operation

    Opamps for 3.3 V operation



    Chapter 6: Filters


    Passive filters

    Active filters

    Low pass filters

    High pass filters

    Combined low pass & high pass filters

    Bandpass filters

    Notch filters

    All-pass filters

    Filter characteristics

    Sallen & Key lowpass filters

    Sallen & Key highpass filters

    Distortion in Sallen & Key filters

    Multiple-feedback bandpass filters

    Notch filters

    Differential Filters


    Chapter 7: Preamplifier architectures

    Passive preamplifiers

    Active preamplifiers

    Amplification and the gain-distribution problem

    Active gain controls plus passive attenuators

    Recording facilities

    Tone controls


    Chapter 8: Variable gain stages

    Amplifier stages with gain from unity upwards: single gain pot

    Amplifier stages with gain from unity upwards: dual gain pot

    Combining gain stages with active filters

    Amplifier stages with gain from zero upwards: single gain pot

    Amplifier stages with gain from zero upwards: dual gain pot

    Switched-gain amplifiers


    Chapter 9: Moving-magnet inputs: levels & RIAA equalisation

    Cartridge types

    The vinyl medium

    Spurious signals

    Other vinyl problems

    Maximum signal levels from vinyl

    Moving-Magnet cartridge sensitivities

    Overload margins and amplifier limitations

    Equalisation and its discontents

    The unloved IEC Amendment

    The ‘Neumann pole’

    MM amplifier configurations

    Opamp MM input stages

    Calculating the RIAA equalisation components

    Implementing RIAA equalisation

    Implementing the IEC amendment

    RIAA series-feedback network configurations

    RIAA optimisation: C1 as a single E6 capacitor, 2xE24

    RIAA optimisation: C1 as 3x10nF capacitors, 2xE24

    RIAA optimisation: C1 as 4x10nF capacitors, 2xE24

    RIAA optimisation: the Willmann Tables

    RIAA optimisation: C1 as 3x10nF capacitors, 3xE24

    RIAA optimisation: C1 as 4x10nF capacitors, 3xE24

    Switched-gain MM RIAA amplifiers

    Switched-gain MM/MC RIAA amplifiers

    Open-loop gain and RIAA accuracy

    Passive and semi- passive RIAA equalisation

    MM cartridge loading & frequency response

    MM cartridge-preamplifier interaction

    MM cartridge DC and AC coupling

    Noise in MM RIAA preamplifiers

    Hybrid MM amplifiers

    Balanced MM inputs

    Noise in balanced MM inputs

    Noise weighting

    Noise measurements

    Cartridge load synthesis for lower noise

    Subsonic filters

    Subsonic filtering: Butterworth filters

    Subsonic filtering: elliptical filters

    Subsonic filtering by cancellation

    Ultrasonic filters

    A practical MM amplifier: #3


    Chapter 10: Moving-coil head amplifiers

    Moving-coil cartridge characteristics

    The limits on MC noise performance

    Amplification strategies

    Moving-coil transformers

    Moving-coil input amplifiers

    An effective MC amplifier configuration

    The complete circuit



    Chapter 11: Tape replay

    The Return of Tape

    A brief history of tape recording

    The basics of tape recording

    Multitrack recording

    Tape heads

    Tape replay

    Tape replay equalisation

    Tape replay amplifiers

    Replay noise: calculation

    Replay noise: measurements

    Load synthesis

    Noise reduction systems

    Dolby HX-Pro


    Chapter 12: Guitar preamplifiers

    Electric guitar technology

    Guitar pickups

    Pickup characteristics

    Guitar wiring

    Guitar leads

    Guitar preamplifiers

    Guitar preamplifier noise: calculations

    Guitar preamplifier noise: measurements

    Guitar amplifiers and guitar effects

    Guitar direct injection


    Chapter 13: Volume controls

    Volume controls

    Volume control laws

    Loaded linear pots

    Dual-action volume controls

    Tapped volume controls

    Slide faders

    Active Volume controls

    The Baxandall active volume control

    The Baxandall volume control law

    A practical Baxandall active volume stage

    Low-noise Baxandall active volume stages

    The Baxandall volume control: loading effects

    An improved Baxandall active volume stage with lower noise

    Baxandall active volume stage plus passive control

    The Overlap Penalty

    Potentiometers and DC

    Belt-ganged volume controls

    Motorised potentiometers

    Stepped volume controls

    Switched attenuator volume controls

    Relay-switched volume controls

    Transformer-tap volume controls

    Integrated circuit volume controls

    Loudness controls

    The Newcomb and Young loudness control


    Chapter 14: Balance controls

    The ideal balance law

    Balance controls: passive

    Balance controls: active

    Combining balance controls with other stages

    Switched balance controls

    Mono-stereo switches

    Width controls



    Chapter 15: Tone controls & equalisers


    Passive tone controls

    Baxandall Tone Controls

    The Baxandall one-LF-capacitor Tone Control

    The Baxandall two-LF-capacitor Tone Control

    The Baxandall two-HF-capacitor tone control

    The Baxandall tone control: impedance and noise

    Combining a Baxandall stage with an active balance control

    Switched-HF-frequency Baxandall controls

    Variable-frequency HF EQ

    Variable-frequency LF EQ

    A new type of switched-frequency LF EQ

    Variable-frequency HF and LF EQ in one stage

    Tilt or tone-balance controls

    Middle controls

    Fixed frequency Baxandall middle controls

    Three-band Baxandall EQ in one stage

    Wien fixed middle EQ

    Wien fixed middle EQ: altering the Q

    Variable-frequency middle EQ

    Single-gang variable-frequency middle EQ

    Switched-Q variable-frequency Wien middle EQ

    Switchable peak/shelving LF/HF EQ

    Parametric middle EQ

    Graphic equalisers


    Chapter 16: Mixer architecture


    Performance factors

    Mixer internal levels

    Mixer architecture

    The split mixing architecture

    The in-line mixing architecture

    A closer look at split format modules

    The channel module (split format)

    Effect return modules

    The group module

    The master module

    Talkback and oscillator systems

    The in-line channel module



    Chapter 17: Microphone preamplifiers

    Microphone types

    Microphone preamplifier requirements

    Transformer microphone inputs

    The simple hybrid microphone preamplifier

    The balanced-feedback hybrid microphone preamplifier

    Microphone and line input pads

    The padless microphone preamplifier

    Capacitor microphone head amplifiers

    Ribbon microphone amplifiers


    Chapter 18: Line inputs

    External signal levels

    Internal signal levels

    Input amplifier functions

    Unbalanced inputs

    Balanced interconnections

    The advantages of balanced interconnections

    The disadvantages of balanced interconnections

    Balanced cables and interference

    Balanced connectors

    Balanced signal levels

    Electronic vs transformer balanced inputs

    Common mode rejection

    The basic electronic balanced input

    Common-mode rejection

    The basic electronic balanced input

    The basic balanced input and opamp effects

    Opamp frequency response effects

    Opamp CMRR effects

    Amplifier component mismatch effects

    A practical balanced input

    Variations on the balanced input stage

    Combined unbalanced and balanced inputs

    The Superbal input

    Switched-gain balanced inputs

    Variable-gain balanced inputs

    Combined line input and balance control stage with low noise

    The Self variable-gain line input

    High input-impedance balanced inputs

    The inverting two-opamp input

    The instrumentation amplifier

    Instrumentation amplifier applications

    The instrumentation amplifier with 4x gain

    The instrumentation amplifier at unity gain

    The instrumentation amplifier and gain controls

    The instrumentation amplifier and the Whitlock bootstrap

    Transformer balanced inputs

    Input overvoltage protection

    Low-noise balanced inputs

    Low-noise balanced inputs in action

    Ultra-low-noise balanced inputs


    Chapter 19: Line outputs

    Unbalanced outputs

    Zero-impedance outputs

    Ground-cancelling outputs: basics

    Ground-cancelling outputs: zero-impedance output

    Ground-cancelling outputs: CMRR

    Ground-cancelling outputs: send amplifier noise

    Ground-cancelling outputs: into a balanced input

    Ground-cancelling outputs: history

    Balanced outputs: basics

    Balanced outputs: output impedance

    Balanced outputs: noise

    Quasi-floating outputs

    Transformer balanced outputs

    Output transformer frequency response

    Output transformer distortion

    Reducing output transformer distortion


    Chapter 20: Headphone amplifiers

    Driving heavy loads

    Driving headphones

    Special opamps

    Multiple opamps

    Opamp-transistor hybrid amplifiers

    Discrete Class-AB headphone amplifiers

    Discrete Class-A headphone amplifiers

    Balanced headphone amplifiers


    Chapter 21: Signal switching

    Mechanical switches

    Input-select switching: mechanical

    The Virtual Contact: mechanical

    Relay switching

    Electronic switching

    Switching with CMOS analogue gates

    CMOS gates in voltage mode

    CMOS gates in current mode

    CMOS series-shunt current mode

    Control voltage feedthrough in CMOS gates

    CMOS gates at higher voltages

    CMOS gates at low voltages

    CMOS gate costs

    Discrete JFET switching

    The series JFET switch in voltage mode

    The shunt JFET switch in voltage mode

    JFETS in current mode

    Reducing distortion by biasing

    JFET drive circuitry

    Physical layout and offness

    Dealing with the DC conditions

    A soft changeover circuit

    Control voltage feedthrough in JFETS


    Chapter 22: Mixer subsystems

    Mixer bus systems

    Input arrangements


    Insert points

    How to move a circuit block


    Improving fader offness

    Post-fade amplifiers

    Direct outputs


    Passive panpots

    The active panpot

    LCR panpots

    Routing systems

    Auxiliary sends

    Group module circuit blocks

    Summing systems: voltage summing

    Summing systems: Virtual-earth summing

    Balanced summing systems

    Ground-cancelling summing systems

    Distributed summing systems

    Summing amplifiers

    Hybrid summing amplifiers

    Balanced hybrid summing amplifiers

    Balancing tracks to reduce crosstalk

    The multi-function summing amplifier

    PFL systems

    PFL summing

    PFL switching

    PFL detection

    Virtual-earth PFL detection

    AFL systems

    Solo-In-Place systems

    Talkback microphone amplifiers

    Line-up oscillators

    The flash bus

    Power supply protection

    Console cooling and component lifetimes


    Chapter 23: Level indication & metering

    Signal-present indication

    Peak indication

    The Log Law Level LED (LLLL)

    Distributed peak detection

    Combined LED indicators

    VU meters

    PPM meters

    LED bargraph metering

    A more efficient LED bargraph architecture

    Vacuum fluorescent displays

    Plasma displays

    Liquid crystal displays


    Chapter 24: Level control & special circuits

    Gain-control elements

    A brief history of gain-control elements


    Operational transconductance amplifiers (OTAs)

    Voltage-Controlled Amplifiers (VCAs)

    Compressors and limiters

    Attack artefacts

    Decay artefacts

    Subtractive VCA control

    Noise gates


    Diode clipping

    Active clipping with transistors

    Active clipping with opamps

    Noise generators

    Pinkening filters


    Chapter 25: Power supplies

    Opamp supply rail voltages

    Designing a ±15V supply

    Designing a ±17V supply

    Using variable-voltage regulators

    Improving ripple performance

    Dual supplies from a single winding

    Power supplies for discrete circuitry

    Large power supplies

    Mutual shutdown circuitry

    Very Large power supplies

    Microcontroller and relay supplies

    +48V phantom power supplies



    Chapter 26: Interfacing with the digital domain

    PCB layout considerations

    Nominal levels and ADCs

    Some typical ADCs

    Interfacing with ADC inputs

    Some typical DACs

    Interfacing with DAC outputs

    Interfacing with microcontrollers


    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.

    "Self provides solid, well-explained technical information throughout the book, all gained from years of experience and a thorough understanding of the entire topic (...) His book exudes skilful engineering on every page, and I found it a very refreshing, enjoyable, and inspirational read (...) if you have the slightest interest in audio circuit design this book has to be considered an essential reference. Very highly recommended." - Hugh Robjohns, Sound on Sound Magazine

    "This book presents a large body of knowledge and countless insider-tips from an award-winning commercial audio designer (...) Douglas Self dumps a lifetime's worth of thoroughly-tested audio circuit knowledge into one biblical tome." - Joseph Lemmer, Tape Op