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Power Amps & AccessoriesHeadphone Amplifiers & Adaptors Preamps & Accessories
Crossovers & DecodersEqualisersPower Supplies
Music Instrument Amps & EffectsMixers, VU Meters, Etc. Digital Audio
Test EquipmentMicrophones & Mic PreampsMiscellaneous
LightingLoudspeaker EQ

No. Power Amplifiers & Accessories Description Date Flags
0360W / 8 Ohm Power Amplifier My old faithful power amp design - For the latest (and much better version), see Project 3A 07Decpcb
1020 Watt Class-A Power amp True Class-A power amp for low power systems or tri-amping 20Feb
12Simple Current F/B Amp An update of a very old 60W / 8 Ohm design (formerly incorrectly referred to as 'El-Cheapo' 12Apr
12aEl-Cheapo This is the real El-Cheapo - presented more or less as originally published (1964). 30W / 8 Ohm design 12Apr
19Single Chip 50W Power Amplifier Using the National Semiconductor LM3876 Power IC. pcb
23Power Amp Clipping Indicator A fast and accurate indicator to show an amp is clipping (Updated) 05May
33Loudspeaker Protection & Muting Protect speakers from turn-on and turn-off transients and amplifier faults. (See important updates to this project) 2007pcb
36Death Of Zen (DoZ) An ultra simple, high performance Class-A power amp.  A lot of people have now built this amp, and all seem very pleased. Revision-A boards are now available. 2005pcb
3A60-100W Hi-Fi Power Amp Updated version of Project 03. Capable of up to 100W into 4 or 8 ohms (with different supply voltages), this amp should satisfy nearly everyone. It has excellent performance, is easy to build, and is a very solid and reliable amplifier. One of the most popular ESP projects. 2009pcb
3B25W Class-A Hi-Fi Power Amp A modified/updated version of Project 3A. Capable of around 25W into 8 ohms, this amp should satisfy those who prefer the idea of a Class-A approach to audio. 2004pcb
53Output Power Limiter Just the thing for hire equipment, or if you want to limit the amplifier power to stop the kids from blowing up your speakers. A simple limiter that can be set to the required power with a trimpot, and no amount of overdrive will exceed the preset power limit. 2000
56Variable Impedance The DoZ project promised the ability to vary the output impedance of the amp, but this is applicable to any amplifier.  Here are the details.  Is it trivial - NO! Is it worth the effort? ABSOLUTELY.  You will never know the possible benefits (or otherwise) until you try it. Apr 12
6155W Hi-Fi Power Amplifier This design is now retired at the author's request n/a
68300W 500W Subwoofer Amplifier By far the biggest (serious) power amp I have published, this amp is designed especially for subwoofers, and is ideally suited for electronically equalised systems 07 Janpcb
7220W/Ch  Stereo IC amplifier Based on the versatile LM1875 from National Semiconductor, this amp is ideal for PC speakers, surround sound, or tweeter amps in triamped systems.  13 Janpcb
76Opamp Based Power Amplifier This is a contributed project, and has some interest value - especially as a learning exercise.  It is simple to build, and will make a good first project. 17 Aug
83MOSFET Follower Power Amplifier Another contributed project that will be of great interest to those who value simplicity and good performance.  Like Project 76, it is simple to build, and will make an excellent first project. 16 Nov
101MOSFET Power Amp This MOSFET power amp has the highest performance of any similar design I have tested, with vanishingly low distortion and wide bandwidth. It is also simpler than most, but lacks nothing as a result. 01 Febpcb
111PIC Based Speaker Protection While P33 has been a very popular project, it does have some limitations. This new version is more versatile, and provides many additional functions. It is of academic interest only at this stage, but PCBs will be made available if there is sufficient interest. 2005
114Class-D Amplifier Complete details for building a stereo (or even a multi-channel) amp or subwoofer amp, using the new ColdAmp BP4078 Class-D amplifier modules. 2005
115GainClone Amplifier This article is in two parts, and describes with photos and drawings how to build a very nice looking GainClone chassis. Using the P19 and (optionally) P88 +P05 boards. 2006pcb
116Class-D Subwoofer amp This describes a complete 'plate' amplifier for subwoofers. Using the P84 equaliser, and either P48 or P71 sub-resonance sub controller. Power is from a ColdAmp BP4078 Class-D amplifier module. These modules (and all PCBs) are available from ESP. Article includes all chassis details. 2006pcb
1171.5kW Power Amp Insanity! This project is designed specifically for those who think that one can never have too much power. Hopefully, after reading this, the constant requests for more power will stop. It is capable of destroying any loudspeaker connected to it, regardless of claimed power rating. 2006
120Crowbar Protection A crowbar loudspeaker protection circuit is the last resort, but if it saves an expensive loudspeaker it will have paid for itself many times over. 2007
127TDA7293 Power Amp A simple to build dual channel power amp, using the TDA7293 Power Opamp ICs. The board for this is very small, making it easy to fit into tight spaces if necessary. 2009
137Powered Box Amplifier A complete preamp, crossover and power amplifiers, designed for powered PA speakers. Can also be used to replace the amp in Leslie cabinets, 'party' systems, etc.
(Note: 3 Part article)
No.Headphone Amplifiers/ AdaptersDescriptionDateFlags
24Hi-Fi Headphone Amplifier Contributed by a reader, this is a very nice circuit - enjoy the best of headphone performance
70DoZ Headphone Amplifier The DoZ is a nice little amp, and it occurred to me that it is ideally suited to headphone use. Using smaller power transistors (and a much smaller heatsink), the performance into headphones is outstanding. Revision-A PCBs are now available. 2005pcb
100Headphone Adaptor This adaptor is intended to provide a headphone output for power amplifiers not so equipped. It is very simple, and is easily adapted to amplifiers of almost any power. 2003
109Portable Headphone Amp This contributed project features crossfeed, and is designed for portable use. It can naturally be used as a mains powered unit as well, and should satisfy most headphone users. 2005
113Hi-Fi Headphone Amp Although there are several other headphone amps, this one is very nice, very flexible, and PCBs are available. It performs extremely well indeed. It is easily adapted to use crossfeed (as a front-end add-on), and runs from a regulated supply for lowest noise 2005pcb
No.Preamps & AccessoriesDescriptionDateFlags
02Simple High Quality Hi-Fi Preamp As it says - simple, high quality preamp.  Has all the facilities normally expected, and is easily modified to your own requirements.   Note: This project is now superseded by Project 88 (but this is still worth reading).2000
06Phono (RIAA) Preamp Very high quality moving magnet phono preamp - few circuits will better this one.  Performance is excellent2013 pcb
25Phono Preamps For All Circuits for moving coil and moving magnet pickups, a range of different equalisation circuits and a complete explanation of RIAA equalisation
32Car Audio Preamp + Artificial Earth Especially for car audio installations. Includes some basic ideas on how to use the artificial earth on other conventional) audio circuits
37Death of Zen Preamp "Minimalist" preamp, with excellent specifications, designed to suit the DoZ (or any other) power amplifier. (see P37-A for latest version)1999
37-ADeath of Zen Preamp (Rev A) Updated version of the 'minimalist' preamp, now uses dual supply rails (use P05 power supply).2007pcb
51Balanced Line Drivers Use these to eliminate hum for long signal leads, or when you cannot eliminate that &*&$$# hum loop from your system2000
80Reverse RIAA Equaliser Do you have an unused phono input?  With this little contributed project, you can use it for any other signal source, or you can test phono preamps for correct equalisation.2001
87Balanced Line Drivers II Some more examples of balanced line transmitters and receivers, with higher performance than those in Project 51.  Don't forget to check out the section "Hey! That's Cheating" - you may be surprised at the findings on this method.2002
88High Quality Audio Preamp - Mk II Project 02 is pretty much past its use-by date now, so I figured it was time for an update. This new version has PCBs available, and its performance is as good or better than the best commercial offerings around. Very flexible design, so the board can be used anywhere a preamplifier is needed. 2002pcb
9178 RPM and RIAA Phono Preamp There is a distinct lack of professional DIY phono preamps that are capable of working with the vast number of different standards that were used for 78 rpm recordings. This project is based on the P06 preamp (and can use the same PCB), and will give results that are second to none2002pcb
97Hi-Fi Preamp Unlike most of my projects, this was designed from the PCB backwards. It is intended for use with PCB mounted pots, and provides Bass, Treble, Balance and Volume controls. A completely new technique for de-sensitising the tone controls gives you full range or very restricted control for minor corrections. 2008pcb
99Subsonic / Rumble Filter - Rev-B Boards A conventional but very effective filter to remove extraneous subsonic noise from vinyl disks, either for listening or transcription to CD. A very steep 36dB/octave filter removes frequencies below 17Hz.2009pcb
104Preamp/ Crossover Muting Circuit A useful addition to any crossover or preamp project that insists on making rude noises - typically just after power is turned off. May be expanded to as many channels as needed, and uses readily available parts.2004
107Phase / Polarity Switch Simple switching circuits to allow normal or inverted polarity of the signal. May be used to experiment with the concept of 'absolute phase', or anywhere else that a switched polarity reversal circuit may be useful.2004
110IR Remote Control Something that readers have been asking for has finally arrived - a complete (simple but functional) infrared remote control for preamps. It provides a driver for a motorised pot for volume and a relay for mute, and short-form kits are available2004pcb
141VCA Based Preamplifier If you need a multi-channel preamp with a single volume control for all, this might be just what you're looking for. Ideal for home theatre! You can have from 2 to 8 channels, or even more if needed. Uses the THAT2180 VCA chip for excellent performance 2013
163Preamp Input Switching Using Relays How to use relays for input switching, including several designs for logic controls to allow push-button input selection Oct 2016 
167 MOSFET Follower & Circuit Protection Many people like their valve (tube) preamps, but if connected to opamp circuits the voltage 'surge' at power-on may cause damage. A MOSFET follower and a muting circuit are also provided Sep 2016 
No.Crossovers & EffectsDescriptionDateFlags
082-Way Electronic Crossover  Conventional 3rd order electronic crossover1999
0924dB/Octave 2/3-Way Xover Linkwitz-Riley alignment and phase coherent !!  This is an extraordinarily nice crossover, and is suited to top of the line hi-fi or professional installations 2007pcb
18Simple Surround Sound Decoder Line-level active and passive versions of the 'Hafler matrix' decoder 1999
21Stereo Width Controllers Two to choose from. Expand or contract the stereo sound stage 1999
26Digital Delay Unit Digital delay, and all the info to construct a complete surround system (Note - The delay IC no longer available) 2012
26ADigital Delay Unit Digital delay, based on the popular PT2399 IC. A very flexible unit with many applications 2012pcb
28Parametric / Sub-Woofer Equaliser A simplified version, which performs surprisingly well and has more options than most of the more complicated circuits 2006
48Sub Woofer Processor Using the ELF™ "Extended Low Frequency" principle, this processor is designed to operate a sub-woofer driver below its resonant frequency.  This means that the box is small, resonance can be (comparatively) high, and the load is completely predictable 2004
48ASub Woofer Processor, Revision A Operates much like the original P48 (above), this new version of the P48 processor is designed to operate a sub-woofer driver below its resonant frequency.  The latest version is far more flexible than the original. (Created 12 Jan 2009) 2009pcb
63Multiple Feedback Bandpass Filter This is the basis of the expandable equaliser and analyser mentioned below as up and coming projects.  Marginally useful in its own right, it is the ideal building block for these projects, and can also be used to build a vocoder! 2000
67Fast Audio Peak Limiter This peak limiter is simple and very effective.  Using a discrete FET as the gain control element gives low distortion and very fast response times. 2000
71Linkwitz Transform Circuit The Linkwitz Transform circuit is an equaliser to provide extended bass response from any loudspeaker in a sealed enclosure.  The effect is similar to the EAS equaliser described in Project 48, but the range is no longer only below resonance, but encompasses the normal frequency range of the driver. 2000pcb
75Constant Q Graphic Equaliser This is a novel constant Q design, that allows the maximum boost and cut to be varied with a single pot.  This project can be made using as many or as few sections as you need. 2001
783-Way 12dB/ Octave Crossover This is a contributed project, and describes a simple high performance 12dB/ Octave crossover network 2001
8112dB/Octave 2-Way Xover Linkwitz-Riley alignment and phase coherent - another very nice crossover where 24dB/ octave is not needed (this uses the P09 PCB, with only a few additional wire links - no tracks to cut) 2007pcb
84Subwoofer Graphic Equaliser This is a constant Q design, with eight 1/3 octave bands covering 20Hz to 100Hz. With up to 14dB boost and cut, even the most recalcitrant subwoofer installation will be brought into line, ensuring the best possible performance. 2009pcb
103Subwoofer Phase Controller A standard phase control circuit. Nothing extraordinary about this project, but after many requests I have finally added it to the list. 12 Mar
12318dB/Octave Crossover A small collection of ideas for building an active 18dB/ Octave crossover network. Includes a scheme for a 'quick and dirty' version that gives a good result for the lowest cost 2009
1254-Way 24dB/Octave Crossover A complete 4-way Linkwitz-Riley crossover, with balanced input stage, individual level controls, on-board regulators and output buffers. 15 Oct 2009 2009pcb
148State Variable Crossover Perfect for loudspeaker system development, or can be used as part of a biamped or triamped system. 12dB/octave continuously variable filters. Aug 2014
155Variable High And Low Pass Filters These circuits are common in mixing consoles, but you might find them useful elsewhere as well. The frequency ranges can be adjusted to suit your needs. Apr 2015
28Parametric / Sub-Woofer Equaliser A simplified version, which performs surprisingly well and has more options than most of the more complicated circuits 2006
48Sub Woofer Processor Using the ELF™ "Extended Low Frequency" principle, this processor is designed to operate a sub-woofer driver below its resonant frequency.  This means that the box is small, resonance can be (comparatively) high, and the load is completely predictable 2004
63Multiple Feedback Bandpass Filter This is the basis of the expandable equaliser and analyser mentioned below as up and coming projects.  Marginally useful in its own right, it is the ideal building block for these projects, and can also be used to build a vocoder! 2000
64Instrument Graphic Equaliser Designed especially as a guitar / bass equaliser, this unit is expandable, and is really a multi-section (23 as shown) tone control.  Offering a wide tonal range and great flexibility, it can be adapted to any musical instrument. 2000
75Constant Q Graphic Equaliser This is a novel constant Q design, that allows the maximum boost and cut to be varied with a single pot.  This project can be made using as many or as few sections as you need. 2001
84Subwoofer Graphic Equaliser This is a constant Q design, with eight 1/3 octave bands covering 20Hz to 100Hz. With up to 14dB boost and cut, even the most recalcitrant subwoofer installation will be brought into line, ensuring the best possible performance. 2009pcb
149Musical Instrument Graphic EQ Guitar, Bass or Keyboard Equaliser. A greatly improved version of Project 64 Aug 2014
150Wien Bridge Based Parametric Equaliser A building block that can be used in mixers, preamps, guitar and bass amps, etc. Sep 2014
153Frequency 'Isolator' EQ 'Isolator' EQ is very common amongst the DJ fraternity, but they can be rather expensive. Now you can build your own, and with all the features you need Nov 2014
No.Power SuppliesDescriptionDateFlags
04Dual Power Supply A power supply that is suitable for most amps of 60W output. Can be adapted or modified to other voltages for more or less power MAINS!
05Preamplifier Power Supply Uses External AC Adapter. Safe and effective, and no hum! (PCB replaced by P05A) 1999
05AUpdated Preamplifier Power Supply All the features of the original P05, plus lower noise and much more versatile 2005
05CUpdated Preamplifier Power Supply All the features of the original P05A plus an improved muting circuit. 2007PCB
15Capacitance Multiplier Supply For Class-A Amps - Extremely low ripple power supply with much less power dissipation than a regulator 2001
38Signal Detecting Auto Power-On Unit When you have a sub-woofer or other equipment that needs to be turned on with the main amp, this is the answer. Detects signal and applies power. 1999Mains Wiring
39Soft Start Circuit Designed for power amps using (large) toroidal transformers, this will limit the inrush current to a sensible value. A PCB is now available for this project, using a new circuit (shown on the project page). 2006PCBMains Wiring
40Load Sensing Auto Switch How to apply power to the entire audio system by turning on one item (typically the preamp). Note that this version is superseded by Project 79. Mains Wiring
43Ultra Simple Split DC Supply When you need a +/- supply, and only have a DC adapter, this little project might just be what you need 1999
44Dual +/-25V Lab Supply Ideal for testing your latest creation, as the voltage can be advanced slowly to ensure that everything works as it should before "real" power is applied. Up to 800mA (typical) output current. Mains Wiring
6912V Switching Supply Ideal for low power applications (such as equalisers or crossovers) in cars, where a +/-12V supply is needed. This project is a perfect starting point for anyone thinking of building a high power switching supply, as it teaches the basics without the risk of expensive things blowing up. 2002
7713.8V Power Supply / Charger A power supply for testing and working on car amplifiers, this unit can be scaled up to about 500 Amps! Easy to build, and ideal for powering any car amplifier for test or service. 2003MAINS!
79Current Sense Auto Power Switch A current sensing switch allows you to turn on multiple devices, just by turning on one master. Use it to activate the entire Hi-Fi by turning on the preamp, or turn on all your PC peripherals when you turn on the computer. 2001MAINS!
89Car Switchmode Supply The little supply (P69) has been here for a while, and here's the big one. This supply is good for up to about 350 Watts, although I suggest that a more modest power of around 250 W is more appropriate for the most part. High current and fully configurable to do what you want. Do not attempt to build this without adequate test equipment or experience. 2002
95Low Power Switchmode Supply This little supply is designed to provide a negative voltage only, allowing you to use the car supply for the positive supply. Current is only about 20mA, but this will be enough to properly power many car audio projects 2002
98Automatic Charger for Battery Hi-Fi Quite a few people like to use a battery supply for preamps especially, since the DC is completely smooth, and batteries are essentially noise free. Unfortunately, they also need to be charged, and this project is designed to disconnect the charger automatically when the preamp is switched on, and re-connect it when the preamp is turned off. 2003
102Simple Pre-Regulator A great many constructors would like to be able to use P05 (Preamp Power Supply) from the main power amp supply, but the voltage is usually much too high. Resistors may be used to drop the voltage, but these must be calculated, and will not allow for any additional load. Using a pre-regulator allows you to reduce the voltage safely, and also provides a significant level of initial hum reduction. 2003
108Switchmode PSU Protection Switchmode supplies are common, but most have no form of protection - especially home made types or many of the cheaper car amplifiers. This contributed project will add protection for over-voltage, under-voltage or high temperatures, and is cheap and easy to build. 2004
118PC Peripheral Switch This ultra simple project uses only a modified power board and a small wiring loom in the PC. By using the PC's 12V supply, it is ultra reliable and cannot false trigger. 2006MAINS!
138Mains Under/ Over Voltage Protection This project senses if the mains voltage falls below or rises above a preset threshold. Designed to protect equipment from extreme mains voltage variations. 2012MAINS!
142Simple High Current Regulator There are some instances where 3-terminal regulators just can't do what you need. This can be due to higher than allowable input voltage or the need for more current than they can provide. This regulator doesn't come with great specifications, but will be more than acceptable for many tasks. 2013MAINS!
144Mains Power Sequencer If you need to turn on/off mains equipment in a preset sequence, this project will be just what you are looking for. Suitable for large PA systems, recording studios, lighting, etc.2013MAINS!
151High Voltage DC Supply If you want to experiment with valve ('tube') circuits, you need a power supply for the B+ and DC for the heaters. (Oct 2014) 0ct 14MAINS!
15612V Trigger Switches Many home theatre receivers (aka audio-visual receivers or 'AVRs') have a 12V trigger output, and the circuits shown can be used to switch on equipment when the trigger voltage is present Apr 15MAINS!
No.Musical InstrumentDescriptionDateFlags
27100 Watt Guitar Amp (Mk II) The new and improved version of the old Project 27 guitar amp. You still need the old one for the cabinet details and such, but the new description and schematics are all here. Preamp (P27B) has been revised, and is now Rev-A. 13 JanMains Wiring
27B100 Watt Guitar Amplifier The original of the unit above. Retained for posterity, and has the speaker box details (may still be needed for the new version). 04 JanMains Wiring
29Tremolo Unit A versatile guitar effect.  This is a simple circuit that gives very good results
34Guitar Spring Reverb Unit A spring reverb unit for guitar amps
45Simple Bass Guitar Compressor An ultra simple compressor, ideally suited for bass guitar. Very simple, but it works very well, and has that really "chunky" sound that many bassists like - one for the experimenter, and really easy to fool about with. Can be used with "ordinary" guitar, too.
47Vox AC30 Simulator Project withdrawn at author's request
49Guitar Vibrato Unit A reasonably simple circuit, with results similar to the famous Vox AC30 guitar amp.  Also has a unique Effect control, allowing some interesting sounds.
64Instrument Graphic Equaliser Designed especially as a guitar / bass equaliser, this unit is expandable, and is really a multi-section (23 as shown) tone control.  Offering a wide tonal range and great flexibility, it can be adapted to any musical instrument. 04Aug
92Guitar and Bass Sustain Unit A compressor/ Limiter for guitar, bass or recorded music. Uses a LED and LDR for low distortion control of the audio level. See Project 145 for details on how to build a linear optocoupler. Feb 07
145Silent Guitar Effects Switching How to use Vactrol® or DIY optocouplers to switch signals in guitar amplifiers. No contact bounce or clicks, just virtually silent switching without any noises. Includes details of how you can build your own LED/ LDR optocoupler. Jul 13
152-1Bass Guitar Preamplifier - Part 1 Part 1 of a very comprehensive bass preamp, with fully adjustable EQ, and all the bells and whistles! There is even the option to use a valve input stage for those who really think there's a difference. There are also overload detection circuits that can be used as and where needed. Mar 15
152-2Bass Guitar Preamplifier - Part 2 Part 2 covers the compression, effects send and return, tuner output and crossover networks for a biamplified bass rig, and a 'tweeter' crossover for those who want to add a horn to get a biting top end. Also describes the soft-clipping circuits. Mar 15
162Voltage Controlled Oscillator A voltage controlled oscillator (VCO) isn't something you need every day, and you may never have thought that you need one. You'd probably be right, but some things are just too interesting to ignore. Jan 16
No.Mixers, Meters etc.DescriptionDateFlags
30Stage and Recording Mixer Able to be built in modular form, allowing as many (or few) channels as desired. Includes effects sends, channel and master inserts, and 3-band EQ with tuneable mid.  This is the most ambitious project so far, in terms of overall complexity - not for the faint of heart ! 2000Mains Wiring
35Direct Injection (DI) Box An essential companion for the mixer for stage or recording work. Includes high and low level inputs. Two different versions to choose from - passive, or active 48V phantom / battery 2005
50Mic Circuit Tester This simple project was inspired by a reader, who needed a small oscillator to check mic circuits during sound setup. It is fixed frequency (tuned to A-440), and provides from 0 to 100mV into a typical microphone input.2000
55PPM and VU Meter A versatile and useful VU meter circuit, that can also operate as a Peak Programme Meter (PPM). See the average and peak output level from an amplifier or preamp.  Can also be used with any mixer. 2006
60LED VU Meter Nothing even remotely special about this LED VU meter, but it is a useful project nonetheless. Includes a simple rectifier circuit to allow full wave detection, and is suitable for line or speaker levels.Feb 08PCB
Universal Preamp/ Mixer
A small preamp and mixer, able to be expanded into 4 stereo input channels. Mic or phono preamps can be added to the front end to make a small and versatile home recording mixer. Includes tone controls. Dec 05pcb
Universal Preamp/ Mixer
Alternative wiring scheme to get more inputs from a single board. Includes tone controls.
05 Decpcb
Phantom Feed Supply
Extremely low ripple and noise were the design goals, and this supply is extraordinarily quiet. Using a simple discrete regulator means no hard-to-get high voltage regulators, and it uses a readily available power transformer as well. Also features a phantom power microphone feed, and a technique to match supply resistors Dec 05pcb
VU Meter Bridge
Build a stereo analogue VU meter to monitor recording or live PA mix levels. Uses the P87A PCB and is compatible with balanced and unbalanced systems.Jan 10pcb
Matrix Mixer
Now you can build a matrix mixer to suit your exact requirements. Uses the P94 Universal Preamp/Mixer PCB. Apr 10pcb
Phase Correlation Meter
More of an experimental circuit than anything else, it should help anyone trying to build a phase meter. Mar 11
Real-Time Analyser
This hardware based real-time audio analyser is a contributed project, based on the multiple feedback bandpass filter described in Project 63 May 11
146Overload/ Clipping Indicator Overload indicator for mixers, preamps or power amps. Simple opamp comparator circuit gives fast response. Nov 13
No.Digital AudioDescriptionDateFlags
85Simple S/PDIF DAC This is quite possibly the simplest possible S/PDIF receiver and DAC you will ever find. Includes audio switching using relays, and for reference, TTL to COAX and COAX to TTL converter schematics are also available. [Contributed Project] Parts now obsolete! 2002
No.Audio Test EquipmentDescriptionDateFlags
11Pink Noise Generator A very clean noise generator for loudspeaker and room acoustics testingFeb 11
16Audio Millivoltmeter For Testing Amplifiers (etc) - An analogue design, 3mV to 30V with dB scale2006
17A-Weighting filter For noise measurements. Ideal for use with the AC Millivoltmeter above2002
22Simple Audio Oscillator For use with the millivoltmeter, for testing amps and speakers2010
31Full Featured Transistor Tester Just the thing to check the transistors for any project 2005
41Opamp Design + Test Board This project will allow you to quickly assemble an opamp circuit for testing. It is very easy and intuitive to use, and an indispensable tool for experimenters (4 opamps)1999
52Distortion Analyser A simple distortion meter you can use with an oscilloscope or millivoltmeter, this project will allow reasonably accurate absolute measurements of THD + Noise (Total Harmonic Distortion), and very useful comparative measurements.2007
58Tone Burst Speaker Measurement Set This project is based on work done by Siegfried Linkwitz (and is reproduced with his kind permission). The project is in three parts - a cosine burst generator (don't worry, it will be explained), a microphone, and a calibrated peak detector. With a suitable audio oscillator, complex and accurate speaker measurements may be made.  This is a fairly complex project, and uses a combination of analogue and digital ICs. The much hoped-for updates have not yet materialised :-(2008
59Self Oscillating Amplifier Excuse me??  No, it is not April!  Based on a idea from a reader, this project allows you to make a power amp oscillate at a defined frequency, eliminating the need for a low distortion oscillator for distortion measurements. Includes a simplified distortion analyser circuit to suit.2000
74Simple RF Probe This simple circuit is indispensable for any RF work. Using just 4 passive components, it uses your multimeter as the measurement display. 2001
82Loudspeaker Test Box A very simple project that allows you to quickly and accurately determine the optimal impedance correction network across a loudspeaker, to ensure that the crossover actually works as you intended. It also allows you to measure impedance. 2001
86Miniature Test Oscillator MiniOsc - A high performance test oscillator, with both sine and square wave outputs. Ideal for bench or portable use, and has low distortion (<0.2%) and a battery drain of less than 2mA from a single 9V battery. Apr 10
106hFE Tester for Transistors An hFE tester with switched collector currents for the Device Under Test, covering a range suitable for the selection and matching of output transistors for amplifiers such as the JLH Class-A, ESP DoZ etc. (contributed project) 2004
119Component Signature Analyser Test components while still installed in a circuit - component signature analysis is an easy way to find faulty parts, especially if you have a working circuit for comparison. Features dual voltage and current ranges, and connects to your oscilloscope (in X-Y mode) to show a graphical indication of the circuit node. 2006
121Inductance Adapter Measure inductance for crossover coils using your multimeter or a frequency counter. Several variations for you to experiment with and end up with a useful tool. 2008
124High Power Dummy Load A dummy load for testing amplifiers (and optionally power supplies). In the full version, it offers impedances from 1 ohm to 16 ohms, with a free-air power rating of up to 360W. This can be extended easily by using cooling as described in the article. 2009
130Reverse A-Weighting This is an odd one - I'm convinced that there's a need for a filter/ amplifier that reverses the A-Weighting curve, but I can't actually figure out what that need might be. Still, if you need one, here it is. May 10
139Mains Current Monitor A versatile, safe and accurate way to measure (and view with an oscilloscope) the mains current drawn by mains powered equipment. This project would appear to be unique - you can't buy a device that does this, but you'll wonder how you survived without it after making one. Oct 12
140True RMS Adaptor The only way to measure non-sinusoidal waveforms is true RMS or errors can be significant. Use this adaptor to get true RMS readings. Dec 12
143Tone Burst Generator/ Gate There aren't many tone-burst generator projects on the Net, and sometimes no other piece of test gear will allow you to run the tests you need. Check amplifier overload recovery, perform non destructive high power speaker tests, plus many more. Apr 13
154PC Oscilloscope Interface PC sound card oscilloscopes can be handy, but you need this circuit to make sure that it doesn't get blown up if you connect it to more than a few volts Apr 15
158Low -Noise Test Preamplifier Every so often, you find that you need to listen to or measure signals that are well below the noise floor of your bench amp or 'scope. With 20, 40 & 60dB of gain, this is what you need.   Aug 15
164Signal Tracer for fault-finding A version of this project was shown in the troubleshooting pages, but it's now a project in its own right. The unit presented here is simple, cheap, and runs from a 9V battery so it can be used almost anywhere.   Jan 16
165Valve Tester for Service Techs If you service valve (tube) amplifiers, you need to be able to test valves under the conditions they are operated under in the amp being fixed. This tester is designed to do just that, but it is not a 'general purpose tester.   Feb 16
No.Microphones and Mic PreampsDescriptionDateFlags
13Low Noise Preamplifier Simple unbalanced design, suitable for microphones - very low noise 1999
66Low Noise Balanced Mic Preamp A discrete front end makes this balanced microphone preamp very quiet, and it has excellent noise rejection.  Since the SSM2017 has been discontinued (sad but true), and if you can't get the INA217 this may be the ideal replacement May 08
93Recording and Measurement Microphones
An introduction to microphones, as well as a variety of powering methods for electret capsules. Phantom powered mic preamps, and more.
May 08
112Dummy Head Recording Microphone Complete details on how to construct a dummy head recording mic. Using either P93 or (surprisingly perhaps) P88 as the mic preamp, the performance is something to surprise you. You will never know just how good a dummy head recording can be until you try it yourself. Dec 06
122Simple Balanced Mic Preamp This is a "utilitarian" preamp. Although not intended where lowest noise is needed, it is still quiet enough for most applications, and will almost certainly be all that's needed for adding a microphone input to an amplifier or powered speaker. Jan 08
1344mA Current Loop Microphone This type of powered mic is quite common for professional measurement microphones, but is not well known outside the noise measurement field. This project provides all the info you need to make your own 4mA current loop mic system. 04 Mar
No.Miscellaneous ProjectsDescriptionDateFlags
01A Better Volume Control A volume control using a linear pot that is much better than most log pots. Also a better balance control.
07Discrete Op-Amp Class-A Output. Intended as an experimental device, but it works extremely well
14Power Amp Bridge Adapter A conventional adapter for bridging power amplifiers Jan 07PCB
20Simplest Ever Bridge Adapter Use this simple method, and avoid external circuits
42Thermo-Fan For Amp Cooling Use a 12V computer fan to keep your amp cool. Uses a simple but very effective diode temperature sensor (Updated) Jan 02
46Thermal Shutdown + Amp Thermal Protection What happens if your amp gets too hot? It will probably self destruct, or at least reduce the life of the power devices. Add this circuit to either turn the amp off, or activate a cooling fan. This is similar to one I use on my own system Mains Wiring
54Low Power FM Transmitter Not really suited for "Bond, James Bond" spying activities, but will be useful to retransmit from the hi-fi to another FM receiver nearby, or use it as a wireless microphone or guitar link. Not in the same league as the commercial offerings, but much, much cheaper. Mar 02
57SIM - The Simple Version Ah!  The simple SIM must be a compromise, you say.  Well, actually the complex version is a compromise - this is the real thing. The smallest variation in amplifier performance will create a signal that the SIM (Sound Impairment Monitor) can react to with startlingly accurate reactions to even the smallest variations in an amplifier. Apr 00
73Hi-Fi PC Sound System A Hi-Fi PC Speaker system? You have never heard your MP3 collection, CD or games sound so good. If you could buy one, a system of this calibre would probably set you back more than the PC itself - The sound is very, very good! PCB
126PWM Dimmer/Speed Control This circuit is a versatile PWM controller for low voltage DC. It can be used to control 12V LED lighting, DC motors, heaters, or anything else that responds to PWM current control. The circuit uses readily available parts, and can even be controlled via C-BUS or other automation systems that support 0-10V control. Oct 09PCB
131Light Activated Switch This has very little to do with audio, but I suppose that you could use it to switch on your hi-fi (instead if a light) when it gets dark. A versatile and easily configured light (or temperature) activated switch. Jul 10
132Air Bearing Linear Tonearm This is a submitted project, and it must be emphasised that it is to be used as a source for ideas for people with machining experience and equipment. There is a considerable amount of work involved, and great scope for either wasting lots of bits of aluminium and other materials, or creating your own variation. If you have the machines - highly recommended. Jul 10
133PA-PC Audio Interfaces If you need to interface from the output of a PC to PA system, or take a recording from the PA when the only thing available is a speaker line, this project shows you how to connect the PC and PA without damaging either. Feb 11
147BJT Muting Switch A little known technique that doesn't look like it could ever work - using bipolar transistors. Dec 13
ABX Comparator
Building on the basic concept of Project X, this contributed project utilises the original techniques of a true ABX tester. It can be made as a simple AB tester, or build the random remote for full ABX testing.
Aug 02
XA-B Switch Box Yes folks, Project "X" has arrived (I just had to have one!). This is a contributed article / project, and might be confronting to some who steadfastly maintain they can hear minute differences between amplifiers. Now is your chance to prove it Aug 00
No.Lighting EquipmentDescriptionDateFlags
62LX-800 Lighting Controller Light is always needed for theatre and live music, and this is just the ticket.  This is an ambitious project, and requires considerable mains wiring - use extreme caution. (Note - opens in a new window) Major Update! 2005Mains Wiring
65Strobe Light Designed as a companion to the lighting controller, but can also be used by itself (or with any other lighting controller).  2006
90Dimmer Control Voltage Reversal Some older Strand dimmer units used a zero to -10V control signal, and the standard analogue control is zero to +10V.  This project allows the easy conversion from one standard to another 2002
1573-Wire Trailing-Edge Dimmer You can't buy these easily, so the only option is to build it yourself. This is the first (and only) fully tested and working design you'll find anywhere.   Jun 2015
1593-Wire Leading-Edge Dimmer You can't buy these easily either, so again the only option is to build it yourself. This is also the first (and only) fully tested and working design you'll find anywhere.   Nov 2015
No.Loudspeaker EQDescriptionDateFlags
48P48 EAS Subwoofer & Controller Although this project is covered elsewhere, it is worth adding it here for convenience. This has proven to be a very popular project since it was first introduced, and that interest has not waned. Using the ELF™ "Extended Low Frequency" principle, this processor is designed to operate a sub-woofer driver below its resonant frequency. This means that the box is small, resonance can be (comparatively) high, and the load is completely predictable. PCBs available
71Linkwitz Transform Circuit The Linkwitz Transform circuit is an equaliser to provide extended bass response from any loudspeaker in a sealed enclosure. The effect is similar to the EAS equaliser described in Project 48, but the range is no longer only below resonance, but encompasses the normal frequency range of the driver. Updated 06 AugPCBs available

Note Carefully

Although I am happy to provide assistance to prospective builders, I cannot (and will not) be drawn into prolonged e-mail exchanges if the project does not work as expected. I can say with complete confidence that all projects presented will work if properly constructed according to the published design. This is not to say that no help will be available - I will always help where I can.

It is inevitable that in some cases (due to component tolerances, for example), a project may require a different value resistor, capacitor (or whatever) to correct for an unexpected variation. Since I cannot control or predict the quality of components sourced by readers, nor the standard of workmanship in assembly, it is not possible to allow for every contingency.

Please do not attempt the construction of any project which you do not fully understand, or if you do not feel completely confident that you can build the project without further assistance. Do not expect me to be able to diagnose an obscure fault remotely, and especially if the project has been modified in any way whatsoever.

Under no circumstances should any reader construct any mains operated equipment unless absolutely sure of his/her abilities in this area. The author takes no responsibility for any injury or death resulting from, whether directly or indirectly, the reader's inability to appreciate the hazards of household mains voltages or other voltages as may be present within the circuitry of a project. Please read the disclaimer now if you have not done so already. Also read the warning on the main projects page. This is important!


Copyright Notice. All projects described herein, including but not limited to all text and diagrams, are the intellectual property of Rod Elliott unless otherwise stated, and are Copyright © 1999 - 2012 (see article for copyright details). Reproduction or re-publication by any means whatsoever, whether electronic, mechanical or electro-mechanical, is strictly prohibited under International Copyright laws. The author / editor (Rod Elliott) grants the reader the right to use this information for personal use only, and further allows that one (1) copy may be made for reference while constructing the project. Commercial use in whole or in part is prohibited without express written authorisation from Rod Elliott and the owner of the copyright in the case of submitted articles.
Page created August 2012 to replace individual pages.