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