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All Material © 1998-2025 Rod Elliott (ESP)
Copyright For Each Individual Article Is Shown At The End Of Each Page
Page Last Updated - November 2025

Articles are sorted alphabetically within categories (also in alphabetical order). All projects are in numerical order.

Indexes

Main Index
Articles Index
Projects Index

Articles

555 Timer Applications
6dB Speaker Crossovers
Active Filters
Active Vs. Passive Crossovers
A-B Blind Comparator
ABX Test Set
Acoustic Feedback & Frequency Shifting
Active Filters Using Gyrators
AM Radio - Wideband/ Hi-Fi
Amplitude Modulation For Simulations
Amplifier Basics - Intro
Amplifier Basics - Part 1
Amplifier Basics - Part 2
Amplifier Basics - Part 3
Amplifier Basics - Part 4
Amplifier Basics - Part 5
Amplifier Basics - Part 6
Amplifier Bridging
Amplifier Classes - Class-A, Class-B, etc.
Amplifier Design
Amplifier Efficiency
Amplifier Power - How much do you need
Amplifier Troubleshooting
Amplifier Troubleshooting - Part 2
Amplifier Protection
Amplifier Sound
Arc Prevention For Switching Circuits
Analogue Vs. Digital
A-Weighting (and why it's wrong)

Baffle Step EQ
Balanced Circuits
Balanced Circuits Part II
Balanced Circuits Part III
Balanced Circuits Part IV
Beginners Guide to Components
Bi-Amplification (Part I)
Bi-Amplification (Part II)
BJT Parameters
Bleeder Resistors in PSUs
Bootstrap Circuits
Bucking Transformers
Bulletin Boards
Buying Electronic Components

Cables - Part 1
Cables - Part 2
Cables - Part 3
Cables - Part 4
Cables - Part 5
Cables - Part 6
Cable Impedance
Cable Information
Capacitors in Depth
Capacitor Coupling In Output Stages
Capacitance Multipliers
Commercial Sound (70-100V Lines)
Compound (Sziklai) Vs. Darlington pairs
Comparators - The Unsung Heroes Of Electronics
Coupling Capacitors
COAX - Introduction To Coaxial Cables
Current Drive Power Amps & Effects on Speaker Drivers
CD Vs. SACD Vs. DVDA
Class-A Amplifiers
Class-A Amplifiers - Part 2
Class-D Amplifier Theory & Design
Class-D Amplifiers (Part II)
Class-G Amplifiers
Compliance Scaling Loudspeakers
Current Transformers (Now in a separate section)

Compression in Audio
Counterfeit Transistors
Crossover Distortion
CFB Vs. VFB (Current Vs Voltage Feedback)
Current Monitors - Detection & Measurement
Current Sources, Sinks & Mirrors

Dangerous Power Supplies
DC Servos - Tips, Traps & Applications
Derived (Subtractive) Crossover Networks
Designing with Opamps - Part 1
Designing with Opamps - Part 2
Designing with Opamps - Part 3
Distortion & Negative Feedback
Distortion - What It Is, How It's Measured
Doppler distortion in Loudspeakers
DSP - Digital Signal Processing in Audio

Earthing (Grounding) Techniques
Electret Microphones, Powering & Uses
Electronics Tools
Electrocution & How To Avoid It
Electret Microphones
Electronic Fuses
Equalisation & How It Works
ESD Protection
Essential Formulae For Electronics
External Power Supplies - New Regulations

FET Applications
FET Circuit Design Process
Followers & Buffers, Various Techniques Examined
Frequency, Amplitude and dB
Fusing & Circuit Protection

Glossary of Terms
Guitar Amps - Repair or Replace
Guitar Speakers - Getting 'the sound'
Guitar pickups - how they're made and what influences the sound.
Guitar Pickup Voltages

Heatsinks
Heatsinks - Selection For Amplifiers
Heatsinks - DIY
HEXFET Audio Amplifiers
High Speed Opamps
Hybrid Relays

IC Power Amplifiers - more power by adding transistors
Impedance
Impedance Compensation for Loudspeakers
Impedance Effects
Inductor/ Capacitor Oscillators
Instrument Amplifiers
Intermodulation Distortion - sum & difference frequencies
Intermodulation Distortion - measurement techniques & effects
Incandescent Lamp Ban
Inrush Current Mitigation
Introduction to Potentiometers
Inrush Current Testing
Inverters - different types explained

JLL Hood Class-A Amp
Linkwitz Transform
LDO (Low Dropout) Voltage Regulators
Lithium Cell Charging & Battery Management
LM358/ LM324 Opamp Distortion Reduction
Lock-In Amplifiers
Logic - A Beginners Guide
Loudspeaker Crossover Design Tables
Loudspeaker Acoustic Centre Offset
Loudspeaker Enclosure Design Guidelines
Loudspeaker L-Pad Calculations
Loudspeaker Power vs. Efficiency

Mains Power Quality
Mains Safety (Essential Reading)
Mathematical Functions Using Analogue Circuits
Meter Attenuators
Meters, Multipliers & Shunts
Microphones
Microphones (Part II)
Microphone Signal Splitters
Miscellaneous Components
Mixing Principles, Active & Passive
MOSFET Relays
Morse Code
Motors - AC and DC
Multimeters - Analogue & Digital
Myths in Audio

Negative Impedance
Neville Thiele Method (NTM™) Crossovers
Noise in Audio Circuits
Notch Filters

Off-Line Flyback Power Supplies
Ohm's Law is Fundamental, but has been corrupted by AI!
Opamp Alternative Circuits
Opamp History
Opamps - Frequency Vs. Gain & Slew Rate
Opamp selection is often controversial, but it need not be
Oscilloscopes. How They Work And Usage
Over-Voltage Protection

Passive Crossovers
Patents - General Information
Passive Line Level Crossovers
Phantom Power - What It Is And How It Works
Phase Angle Vs. Transistor Dissipation
Phase Correction - Myth or Magic?
Phase, Time & Distortion
Phone Plugs and Sockets
Power Amplifier Clipping Behaviour
Power Amplifier Development Over The Years
Power Ratings
Power Supply Design
Power Supply Simulation
Power Supply Snubbers
Power Supply Snubbers II
Power Supply Design (Part II)
Pre-Regulators
Projects, DIY & Sustainability

Rectifiers - Selection & Usage
Relays - Part 1
Relays - Part 2
Relays - Part 3
Reverberation Tanks
Review of BE Valve Amplifier

Satellites & Subs (QB5 Alignment)
Safe Operating Area (SOA)
Sinewave Oscillators - Characteristics, Topologies, Examples
Servos - Hobby Servos, ESCs And Tachometers
(The) Subwoofer Conundrum
Series vs. Parallel Crossovers
Small Power Supplies (Part I) - Low Current, Including 'Off-Line'
Small Power Supplies (Part 1I) - Transient Response & Noise
Small Satellite Speaker (Part 1)
Small Satellite Speaker (Part 2)
Small Satellite Speaker (Part 3)
Soft Clipping Circuits
Soft Start Circuits
Solid State Relays
Sound Impairment Monitor
Sound - Illusion?
State Variable Filters
Speaker Failure
Squarewave Testing Amps & Filters
State of Manufacture
Switchmode Power Supplies (Part II)
Switch De-Bounce Techniques

Transistor Matching
Transistor listing
Transformers and mains DC offset
Transformers - Part 1
Transformers - Part 2
Transformers - Part 3
Transformers - Part 4
Transformers - The Variac
Transformers for 'Line Level' Audio
Transformerless PSUs
Thermistor Selection
Thiele-Small Parameters
Time Alignment With Phase Shift Networks Triamped Speaker System - Part 1
Triamped Speaker System - Part 2

Useless Designs - Online crap to be avoided

Voltage Dividers & Attenuators
Volume Filling Reflex Enclosures

What Makes Tweeters Blow
What Is Hi-Fi
Why Do It Yourself?
Wiring A Power Supply
Waveguides, Part 1
Waveguides, Part 2
Waveguides, Part 3

Yellow Glue

Valves

Valve Articles Index
Valve Amps - Do they really sound different?
Valve intro - types, terminology, etc.
Bias and Gain
Valve Stage Analysis
Design Considerations - Part 1
Design Considerations - Part 2
Low Distortion Preamps
Valve Myths
High Voltage DC Supply
High Voltage Time Delay

Application Notes

Application Notes Index
Precision Rectifiers
Analogue Metering Amplifiers
High Power Led SMPS
Car Dome Light Extender
Zero Crossing Detectors
Ultra-Simple SMPS
Transistor Assisted Zener
Using Zener Diodes
DC Motor Speed Controller
DC Motor Speed Controller (II)
2-Wire/4-Wire Converters
4-20mA Current Loop Interfaces
Peak, Average and RMS Measurements
Reverse Polarity Protection
Peak Detection Circuits
Input Overvoltage Protection
Measuring Ultra-High Resistance
DC Detectors For Loudspeaker Protection
Ultra-Low Leakage Diodes
'Zero Power' LED battery Indicator
Mains Peak Voltage Detectors

Purchases

Ordering Info
Price List
Fully Built Modules
Guitar Amp Module
Digital Flash Module
VP-103 Valve Preamp
PayPal Details
Western Union Details
Dead Letters

Clocks

Clock Components
Clock Motors
Kundo Battery Clocks
Old Synchronous Motors
Frequency Changer
Build a Synchronous Clock
Free Pendulum Clock
1.5V Mains Supply
Magnet Charger
Simple Flux Meter
Spark Quench Circuits
1 second timebase
Fast Demagnetiser
Arduino Based Slave Clock Driver

Gallery

Gallery Index
L-R Crossover (2)
Reader Feedback - Part 1
Reader Feedback - Part 2

Downloads

Crossover Calculator (EXE)
Download Index
Heatsink Calculator (ZIP)
Heatsink Design (XLS)
LED LM3915 VU Design (ZIP)
MFB Filter Calculator (EXE)
Loudspeaker Parameters (ZIP)
Crossover Design (ZIP)
Linkwitz Transform Design (ZIP)
PC Timer Program (EXE)
Reminder Program (EXE)
Semiconductor Data (EXE)
Serial/ Parallel Resistor Calc. (ZIP)
Transformer analysis program (ZIP)
Transformer analysis spreadsheet (ZIP)
Transformer design program (ZIP)

Humour

Humour Index
Humour - Part 1
Humour - Part 2
Murphy's Laws
A Space Oddity
If Your O/S Were an Airline
Waltzing Matilda Explained
Monty Python
Dynamic Range Vs. Ambient Noise
Satcure Products

Miscellaneous

Hall of Shame
Home Page
Main Index
Main Links Page
Mad As Hell - Part 1
Mad As Hell - Part 2
Mad As Hell - Part 3
Mad As Hell - Part 4
ESP Ethics Policy
About ESP Site
Contact the Author
Submit Your Material
Contracting Details
About the Author
Custom Projects for Education
Frequently Asked Questions
Spam, Scams & Security
Scams - how they work
Your on-line security
Spam, Spam, Spam, Spam
Disclaimer
Search Page
Contribute Project/ Article
Project Cost Estimates

TCAAS (The Class-A Amplifier Site)

The JLH Class-A Amplifier
Other JLH Amplifier Designs
Other Class-A Amplifiers
Classic Class-B Schematics
JLH Power Amp Schematics
The Published Articles of John Linsley Hood

Lamps, PSUs, Energy

Lamps - Incandescent, etc.
Capacitance, Inductance & Non-Linear Loads
Dimmers
Dimmers - Part 2
Dimmers With LED Lighting
Electronic Transformers
ESL (Electron Stimulated Luminescence) Lamps
External Power Supplies
Fluorescent Lamps
Induction Fluorescent Lamps
Inrush Current Protection
LED Lighting
LED Lighting - Thermal Design
Sulphur Plasma Lamps
Power Calculations - Watts, VA (AC or DC)
Power Factor Correction
Power Saver Scam
Wind Turbine Introduction
Wind Turbine Noise

Projects

Projects Index
Projects Index by Category
Project List in Numerical Order

00 Opamp Bypassing
01 Better Volume Control
02 Simple Preamp
02 60W Power Amp
04 Power Amp Supply
05 Preamp Power Supply
05A Updated Preamp Power Supply
05-Mini Budget Preamp Power Supply
06 Phono Preamp
07 Discrete Opamp
08 3rd Order Electronic Crossover
09 Linkwitz-Riley Crossover

10 Class-A Amplifier
11 Pink Noise Generator
12 Current Feedback Power Amp
12A El-Cheapo Power Amp
13 Low Noise Preamp
14 Power Amp Bridging
15 Capacitance Multiplier
16 Audio Millivoltmeter
17 A-Weighting Filter
18 Surround Decoder
19 50W IC Power Amp

20 Simple Bridge Adaptor
21 Stereo Width Controllers
22 Audio Oscillator
23 Clipping Indicator
24 Headphone Amplifier
25 Phono Preamps For All
26 Digital Delay
26A PT2399 Digital Delay
27 Guitar Amp (Original)
27 Guitar Amp (Part 1)
27 Guitar Amp (Part 2)
28 Quasi-Parametric EQ
29 Tremolo Unit

30 Mixing Desk (Part 1)
30 Mixing Desk (Part 2)
30 Mixing Desk (Part 3)
30 Mixing Desk (Part 4)
30 Mixing Desk (Part 5)
31 Transistor Tester
32 Car Audio Preamp
33 Speaker Protection and Mute
34 Spring Reverb Unit
35 Direct Injection Box
36 DoZ Class-A Amplifier
37 DoZ Preamp
38 Auto Power-On
39 Soft Start Power Switch
3A 60W Hi-Fi Power Amp
3B 25W Class-A Power Amp

40 Load Sensing Auto Switch
41 Opamp Design & Test Board
42 Thermo-Fan Controller
43 Simple DC Split Supply
44 Dual Lab Supply
45 Bass Compressor
46 Thermal Shutdown
47 VOX AC30 Simulator (withdrawn)
48 Sub Equaliser
49 Guitar Vibrato

50 Mic Circuit Tester
51 Balanced Line Drivers
52 Distortion Analyser
53 Power Limiter
54 Low Power FM Transmitter
55 PPM and VU Meters
56 Variable Amp Impedance
57 Sound Impairment Monitor
57 Speaker Measurement Set
59 Self Oscillating Amp

60 LED VU Meter
61 (Withdrawn)
62 Lighting System (Part 1)
62 Lighting System (Part 2)
62 Lighting System (Part 3)
62 Lighting System (Part 4)
62 Lighting System (Part 5)
62 Lighting System (Part 6)
63 MFB Filter
64 Instrument Graphic EQ
65 Strobe Light
66 Balanced Mic Preamp
67 Audio Peak Limiter
68 Sub Power Amp
69 Low power +/-12V supply

70 DoZ Headphone Amp
71 Linkwitz Transform Circuit
72 20W IC Stereo Amp
73 PC Sound System
74 RF Probe
75 Constant Q Graphic EQ
76 Opamp Based Power Amp
77 High Current 13,8V Supply
78 2nd Order Electronic Crossover
79 Current Sense Power Switch

80 Reverse RIAA Equaliser
81 12dB L-R Crossover
82 Loudspeaker Test Box
83 MOSFET Follower Amplifier
84 1/3 Octave Sub Equaliser
85 S/PDIF DAC
86 Mini Audio Oscillator
87 Balanced Transmitters & Receivers
88 Audio Preamp
89 Car Switchmode Supply

90 Dimmer Polarity Reversal
91 78RPM Phono EQ
92 Guitar and Bass Sustain
93 Recording & Measuring Mic
94 Universal Preamp Mixer
95 Low Power -VE Supply
96 48V Phantom Supply
97 Hi-Fi Preamp
98 Auto Charger for Battery Hi-Fi
99 36dB/ Octave Infrasonic ('Subsonic') Filter

100 Headphone Adaptor for Amplifiers
101 200W MOSFET Power Amplifier
102 Simple Pre-Regulator
103 Subwoofer Phase Control
104 Preamp/ Crossover Mute Circuit
105 Build an Electrostatic Loudspeaker (ESL)
106 h_FE Tester for Transistors
107 Phase / Polarity Reversal Switching
108 Switchmode PSU Protection
109 Headphone Amp

110 IR Remote Control
111 PIC Speaker Protection
112 Dummy Head Microphone
113 Hi-Fi Headphone Amp
114 Class-D (PWM) Power Amp
115 GainClone Amplifier (Part 1)
115 GainClone Amplifier (Part 2)
116 Class-D Subwoofer Amp
117 1.5kW Power Amplifier
118 Ultra Simple PC Peripheral Switch
119 Component Signature Analyser

120 Crowbar Speaker Protection
121 Reading Inductance
122 Ultra-Simple Mic Preamp
123 18dB/Octave Crossover
124 Dummy Load
125 4-Way 24dB/Octave Crossover
126 10A, 12V PWM dimmer/ speed controller
127 Two Channel TDA7293 power amplifier
128 Analogue VU Meter Bridge
129 Matrix Mixer

130 Inverse A-Weighting Filter
131 Light Activated Switch
132 Air Bearing Tonearm
133 PA-PC Audio Interfaces
134 4mA Current Loop Microphone
135 Phase Correlation Meter
136 Real-Time Audio Analyser
137 Bi-amped PA Amplifier
138 Mains Over/ Under Voltage Cutout
139 Mains Current Monitor
139A Simple Current Monitor

140 True RMS Adaptor
141 VCA Based Preamplifier (THAT2180)
142 Simple High Current Regulator
143 Tone Burst Generator/ Gate
144 Mains Power Sequencer
145 Silent Guitar Effects Switching
146 Overload/ Clipping Indicator
147 BJT Muting Switch
148 State Variable Crossover
149 Musical Instrument Graphic EQ

150 Wien Bridge based equaliser
151 High Voltage DC Supply
152 Bass Guitar Amplifier - Part 1
152 Bass Guitar Amplifier - Part 2
153 Frequency 'Isolator' EQ
154 PC Oscilloscope Interface
155 Variable High And Low Pass Filters
156 12V Trigger Switches
157 3-Wire trailing-edge light dimmer
158 Low-Noise Test Preamplifier
159 3-Wire Leading-Edge Dimmer

160 LM386, LM380 & LM384 Power Amplifiers
161 High Impedance Input Stages
162 Voltage Controlled Oscillator
163 Preamp Input Switching Using Relays
164 Signal Tracer
165 Valve Tester for Service Techs
166 Push-on, Push-off Mains Switch
167 MOSFET Follower & Circuit Protection
168 Low Ohms Meter
169 Battery Powered 'Audiophile' Amplifier

170 6dB/ Octave Active Crossover
171 Infrasound Translator
172 Wattmeter for AC Power Measurements
173 Constant Directivity Horn Equaliser
174 Ultra-Low Distortion Oscillator
175 Single Supply BTL Amp DC Protection
176 Fully Differential Amplifier
177 Constant Current Transistor Tester
178 Low Voltage Power Amplifier
179 Filament Lamp Stabilised Wien Bridge Oscillator

180 Amplifier 'Power Meter'
181 Audio Accelerometer
182 Maximum Length Sequence (MLS) Noise Generator
183 Signal Detecting Audio Ducking Unit
184 Li-Ion Battery Cutoff For Electronics Projects
185 Speaker, Microphone & Circuit Polarity Tester
186 Workbench Test Amplifier
187 Moving Coil Head Amplifier
188 Surround Sound Decoder (Mk II)
189 Audio Wattmeter (Measures True Power)

190 Microphone (including phantom powered) Muting Circuit
191 Peak Voltage & Current Detector For Loudspeakers
192 12V to ±12V Switchmode Supply
193 12V to P48 Phantom Power Supply
194 Withdrawn
195 Guitar 'Talk Box'
196 12V Float-Charge Battery Supply
197 Low Frequency Boost And High Pass Filter For Speaker EQ
198 MOSFET Relay
199 ABC New Years Eve Concert Equaliser

200 DIY LDR Optocoupler
201 Multi-Channel Trailing-Edge Dimmer
202 Piezo Preamplifiers
203 Guitar/ Studio Spring Reverb Unit
204 Frequency Shifter For Acoustic Feedback Reduction
205 4-Channel Mixer For Microphones Or Instruments
206 Guitar Vibrato/ Tremolo Unit
207 High Current AC Source
208 Amplifier Powered DC Protection Circuit
209 Resistor And Capacitor Decade Boxes

210 Electronic Fuse Circuits For DC and AC
211 Reverb Drive And Recovery Amplifier
212 High Impedance DC Voltmeter
213 DIY voltage controlled amplifier (VCA)
214 'Zero Capacitance' Guitar Lead
215 'P27-Revisited' 40W Guitar Amp
216 Speaker Emulator Dummy Load
217 Low Power 'Practice' Amplifier
218 High Q Gyrator Filter
219 Valve Guitar Amp Speaker Switch

220 Switchmode Buck Converter
221 Tweeter Amp Voltage Regulator
222 Transformerless Soft Start Power Switch
223 Dual Bench Power Supply
224 External In-Line Inrush Limiter
225 Inrush Current Test Unit
226 Versatile Tone Controls
227 Hybrid Relay For Speaker Protection
228 Negative Impedance Test Amplifier
228A Negative Z Test Amp Annex
229 Enhanced Reverb Mute System

230 Workbench Signal Routing Panel
231 Fast Discrete Opamp
232 Distortion Measurement System
233 Isolated Power DC-DC Supplies
234 Resistor Substitution Box
235 Current Feedback Opamp (DIY)
236 AC Millivoltmeter
237 JFET Test System
238 High Voltage, Low Current DC Source
239 Signal Detecting Power-On (Mk II)

240 10 Watt Audio Amp/ DC Supply
241 Z-Weighting Filter
242 Cosine Burst Generator (Mk II)
243 'Retro' Hi-Fi System
244 3-LED Level Indicator
245 TPSI3052-Q1 MOSFET Relay
246 Clipping Indicator
247 Tape Head Preamp
248 Low-Voltage Charge Pumps
249 Guitar Booster Circuits

250 Inductor Saturation Tester
251 Protected DC Load
252 6-Band Guitar EQ
253 18dB/Octave State Variable Xover
254 24/18dB Octave Asymmetrical Xover
255 Another MOSFET relay, using everyday parts
256 Transformer-Based DI Box with VU Meter
257 Motor Rotation Detector (Safety)
258 Non-Contact Current Detector (Workshop)

ABX ABX Comparator
X A-B Switch Box

Project Suggestions

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