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 Elliott Sound Products Audio Project Pages 

Numerical Index of Projects
Page Last Updated - July 2020

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Main IndexMain Index
Projects IndexProjects Index
Projects by CategoryProjects Sorted By Category

Troubleshooting - part 1Troubleshooting and Repair Guide - Part 1 ... introduction, general principles and power amps
Troubleshooting - part 2Troubleshooting and Repair Guide - Part 2 ... preamps, crossovers and other opamp circuits

Projects 1-9   10-19   20-29   30-39   40-49   50-59   60-69   70-79   80-89   90-99   100-109   110-119   120-129   130-139   140-149   150-159   160-169   170-179   180-189   190-200   200-

The Date column usually indicates the date of initial publication, and there have been updates to many of the projects that are not reflected by the date shown.  Where possible, the date of initial publication and the update are both shown.  Because there are so many projects, it's proved difficult to ensure that the last update is shown.  Many of the projects are 'timeless', and a very early publication date doesn't mean the project is obsolete.  Most are in chronological order, but there are a few exceptions.  Use 'CTRL-F' to search within the page.

There are currently two projects that will get PCBs (shown as Pending) once the COVID-19 pandemic has settled down.  At present, orders are almost nil, and I can't afford to have boards made that won't be sold in the current conditions.

No.Project DescriptionDatePCB
01A Better Volume Control A volume control using a linear pot that is much better than most log pots1999
02 Simple High Quality Hi-Fi PreampAs it says - simple, high quality preamp.  Has all the facilities normally expected1999
03 60W / 8 Ohm Power Amplifier(Updated) My old faithful power amp design. - See Project 3A1999PCB
04 Dual Power SupplyA power supply that is adaptable for most power amps1999
05 Preamplifier Power SupplyUses External AC Adapter.  Safe and effective (replaced by P05-Mini).1999 
05A Preamplifier Power SupplyAll the features of the P05, but much more versatile.  Includes 'Loss of AC' detector.2005 
05C Preamplifier Power SupplyAll the features of the original P05B plus an improved muting circuit.2007PCB
05-Mini Preamplifier Power SupplyFlexible, low-cost PSU for preamps or general test work.  This is a new PCB that replaces the original P05 board, because some builders just want a simple PSU. 2017PCB
06 Phono (RIAA) PreampVery high quality moving magnet phono preamp - few circuits will better this one.1999PCB
07 Discrete Op-AmpClass-A Output.  Intended as an experimental device - works extremely well1999
08 2-Way Electronic Crossover Conventional 3rd order electronic crossover1999
09 24dB/Octave 2/3-Way XoverLinkwitz-Riley alignment.  This is the optimum choice for any active system - Rev-B boards1999PCB
9a A Reader's XoverThis is well worth reading if you can't decide on biamping1999
10 20 Watt Class-A Power ampTrue Class-A power amp for low power systems or tri-amping1999
11Pink Noise Generator For loudspeaker and room acoustics testing1999
12Current Feedback Amp An updated version of a very old 60W / 8 Ohm design1999
12aEl-Cheapo This is the real El-Cheapo, presented in more or less original form1999
13Low Noise Preamplifier Simple unbalanced design, suitable for microphones - very low noise1999
14Power Amp Bridge Adapter A conventional adapter for bridging power amplifiers1999PCB
15Capacitance Multiplier Supply Extremely low ripple supply with less power dissipation than a regulator1999
16Audio Millivoltmeter For Testing Amplifiers (etc) - An analogue design, 3mV to 30V with dB scale1999
17A-Weighting filter For noise measurements.  Ideal for use with the AC Millivoltmeter above1999
18Simple Surround Sound Decoder A line-level version of the "Hafler matrix" decoder1999
19Single Chip 50W Power Amplifier Using the National Semiconductor LM3876/ LM3886 Power IC.1999PCB
20Simplest Ever Bridge Adapter Use this simple method, and avoid external circuits1999
21Stereo Width Controllers Two to choose from.  Expand or contract the stereo sound stage1999
22Simple Audio Oscillator For use with the millivoltmeter, for testing amps and speakers1999
23Power Amp Clipping Indicator A fast and accurate indicator to show an amp is clipping1999
24Hi-Fi Headphone Amplifier Contributed by a reader, this is a very nice circuit1999
25Phono Preamps For All Various circuits for moving coil and moving magnet pickups1999
26Digital Delay Digital delay  Retained for information only - The Mitsubishi delay IC is no longer available1999
26ADigital Delay Unit Digital delay using PT2399 - Note: PCB (with IC) available now1999PCB
27100 Watt Guitar Amp (Mk II) The new and improved version of the original Project 27 guitar amp (now 27b).1999PCB
27b100 Watt Guitar Amplifier The original of the unit above.  Retained for posterity, and has speaker box details1999
28Parametric / Sub-Woofer Equaliser A simplified version, which performs surprisingly well1999
29Tremolo Unit A versatile guitar effect.  This is a simple circuit that gives very good results1999
30Stage and Recording Mixer Able to be built in modular form, allowing as many (or few)  channels as desired.1999
31Full Featured Transistor Tester Just the thing to check the transistors for any project1999
32Car Audio Preamp + Artificial Earth Especially for car audio installations, can be used for any single supply system1999
33Loudspeaker Protection and Muting Protect speakers from turn-on and turn-off transients and amplifier faults1999PCB
34Guitar Spring Reverb Unit A high performance spring reverb unit for guitar amps1999
35Direct Injection (DI) Box An essential companion for the mixer for stage or recording work1999
36Death Of Zen (DoZ) An ultra simple, high performance Class-A power amp.  Revision-A boards now shipping1999PCB
37Death of Zen Preamp "Minimalist" preamp, designed to suit the DoZ (or any other) power amplifier1999PCB
37ADeath of Zen Preamp Updated "minimalist" preamp, designed to suit the DoZ (or any other) power amplifier1999PCB
38Signal Detecting Auto Power-On Unit For equipment to be turned on with the main amp.  Detects signal and applies power.1999
39Soft Start Circuit Designed for (large) toroidal transformers, limit the inrush current to a sensible value.1999PCB
3A60-100W Hi-Fi Power Amp 100W into 4 or 8 ohms.  Has excellent performance, and is easy to build.1999PCB
3B25W Class-A Hi-Fi Power Amp Up to 25W into 8 ohms.  Using the same PCB as P3A, the Class-A version is a good performer, and is easy to build.1999PCB
40Load Sensing Auto Switch Apply power to the system by turning on one item.  Superseded by Project 79.1999
41Opamp Design + Test Board Quickly assemble an opamp circuit for testing.  Very easy and intuitive to use1999
42Thermo-Fan For Amp Cooling Use a 12V computer fan to cool your amp.  Uses diode temperature sensor1999
43Ultra Simple Split DC Supply When you need a +/- supply, and only have a DC adapter1999
44Dual +/-25V Lab Supply Up to 800mA (typical) output current at +/-25V.2000
45Simple Bass Guitar Compressor An ultra simple compressor, ideally suited for bass guitar.2000
46Thermal Shutdown/ Protection Add this circuit to either turn the amp off or activate a cooling fan if it overheats2000
47WithdrawnDetails no longer available 
48Sub Woofer Processor Designed to operate a sub-woofer driver below its resonant frequency.2000
48ASub Woofer Processor (Rev-A) New version of the sub-woofer driver has far greater flexibility.2000PCB
49Guitar Vibrato Unit A reasonably simple circuit, with results similar to the Vox AC30 guitar amp2000
50Mic Circuit Tester Small oscillator to check mic & line circuits during sound setup2000
51Balanced Line Drivers Use these to eliminate hum for long signal leads2000
52Distortion Analyser A simple distortion meter you can use with an oscilloscope or millivoltmeter2000
53Output Power Limiter Just the thing if you want to limit amplifier power to something 'sensible'2000
54Low Power FM Transmitter Useful to retransmit the hi-fi to another FM receiver nearby, or as a wireless mic2000
55PPM and VU Meter A versatile and useful VU meter circuit, can also operate as a Peak Program Meter 2000
56Variable Impedance Modify the output impedance of an amplifier with these simple ideas (Updated) 2012
57SIM - The Simple Version The smallest variation in amplifier performance is shown with this simple circuit2000
58Tone Burst Speaker Measurement Set Based on work done by Siegfried Linkwitz (reproduced with his permission).  See Project 143 for a conventional Tone Burst generator2000
59Self Oscillating Amplifier Allows you to make a power amp oscillate at a defined frequency for testing2000
60LED VU Meter Standard LED VU meter, includes simple rectifier circuit for full wave detection2000PCB
61WithdrawnDetails no longer available 
62LX-800 Lighting Controller Light is always needed for theatre and live music, and this is just the ticket2000
63Multiple Feedback Bandpass Filter This is the basis of an expandable equaliser and analyser or vocoder2000
64Instrument Graphic Equaliser Designed especially as a guitar / bass equaliser, this unit is expandable2000
65Strobe Light Designed as a companion to the LX800, can also be used by itself 2000
66Low Noise Balanced Mic Preamp A discrete front end makes this balanced microphone preamp very quiet2000PCB
67Fast Audio Peak Limiter This peak limiter is simple and very effective.  Uses discrete FET gain control 2000
68300W Subwoofer Amplifier This amp is designed especially for subwoofers2000PCB
69Switchmode Car Power Supply Low power +/-12V supply for car preamps and equalisers (etc.)2000
70DoZ Headphone Amplifier The DoZ is ideally suited to headphone use.  Revision-A boards now shipping2000PCB
71Linkwitz Transform Circuit The Linkwitz Transform circuit - an equaliser to provide extended bass response2000PCB
7220W/Ch  Stereo IC amplifier Based on the versatile LM1875 from National Semiconductor2001PCB
73Hi-Fi PC Sound System You have never heard your MP3 collection, CD or games sound so good2001PCB
74Simple RF Probe Indispensable for any RF work.  Uses just 4 passive components2001
75Constant Q Graphic Equaliser Constant Q design.  Can be made using as many or as few sections as needed.2001
76Opamp Based Power Amplifier This is a contributed project, and has some interest as a learning exercise2001
7713.8V Power Supply / Charger A supply for testing and working on car amplifiers - up to about 500 Amps!2001
783-Way 12dB/ Octave Crossover Contributed project, simple 12dB/ Octave crossover network.2001
79Current Sense Auto Power Switch A current sensing switch turns on multiple devices from one master2001
80Reverse RIAA Equaliser Test phono preamps for correct equalisation, or convert unused phono inputs.2001
8112dB/Octave 2-Way Xover Linkwitz-Riley alignment and phase coherent (uses the P09 Rev-B PCB)2001PCB
82Loudspeaker Test Box Quickly and accurately determine the optimal impedance correction network2001
83MOSFET Follower Power Amplifier Another contributed project that may be of great interest2001
84Subwoofer Graphic Equaliser This is a constant Q design, eight 1/3 octave bands covering 20Hz to 100Hz.2001PCB
85Simple S/PDIF DAC Quite possibly the simplest possible S/PDIF receiver and DAC you will ever find2001
86Miniature Audio Oscillator The Miniosc - low distortion battery powered audio oscillator2002PCB
87Balanced Transmitter / Receiver Updated and upmarket versions of the Project 51 balanced circuits2002PCB
88High Quality Audio Preamp An audiophile quality preamp, with full switching and programmable gain2002PCB
89Switchmode Power Amp Supply A high power (350W typical) car power amplifier supply2002
90Dimmer Control Polarity changer Convert old dimmer units using a 0 to -10V control signal2002
9178 RPM and RIAA Phono Equaliser Multi Standard 78 RPM and RIAA Phono Equaliser handles all 'standards'2002PCB
92Guitar and Bass Sustain A simple, low distortion limiter for musical instruments2002
93Recording & Measurement Microphone A selection of projects for making your own mics for recording and/ or measurement (includes PCB Version of P93)2002PCB
94Universal Preamp/ Mixer A small and versatile mixer and preamp, suitable for many uses.2002PCB
94AUniversal Preamp/ Mixer Alternative wiring for the versatile mixer/ preamp, suitable for many uses.2002PCB
95Low Power -Ve Supply Low power -ve supply for car audio preamps and crossovers2002
9648V Phantom Supply Low noise 48V regulator and phantom mic supply circuits.2002PCB
97Hi-Fi Preamp Another preamp, but this one has tone controls, and all pots are PCB mounted2002PCB
98Battery Charger Automatic Charger for Battery Operated Hi-Fi Preamps2003
99Subsonic/ Rumble Filter A 36dB/octave 17 Hz high pass filter to remove ultra low frequencies (Published 2003)  Rev-B PCB2009PCB
100Headphone Adaptor A simple adaptor to provide a headphone output to an existing power amplifier2003
101MOSFET Power Amp 200W MOSFET Hi-Fi Power amplifier (Published 2003)2012PCB
102Simple Pre-Regulator Use this to adapt P05 to a power amp supply for your preamp   (Published 2003) - added 'enhanced' version 2016
103Subwoofer Phase Control A standard phase control for use with subwoofers.2004
104Preamp/ Crossover Muting Circuit Muting circuit suitable for all line-level applications.2004 
105WithdrawnDetails no longer available  
106hFE Tester An hFE tester with switched collector currents for the Device Under Test2004 
107Polarity Reversal Switch Switch the absolute polarity (180° phase shift) of signals with this simple circuit2004 
108Switchmode PSU Protection This contributed circuit can help prevent failure of your switching power supply.2004 
109Portable Headphone Amp Another contributed circuit, this is a complete portable headphone amp that features crossfeed.2004 
110IR Remote Control Volume and mute are provided by this simple but functional circuit.  Suitable for all preamps.2004PCB
111PIC Speaker Protection This doesn't replace P33, but it is possibly the ultimate speaker protection.2005
112Dummy Head Recording Microphone Surprise yourself with one of the most realistic recording processes known.2005PCB
113Hi-Fi Headphone Amp Yet another headphone amplifier, but this one has PCBs available2005PCB
114PWM Power Amplifier Based on the ColdAmp BP4078 400W module, Class-D is here.  Definitely worth looking at!2005PCB
115GainClone Amplifier Complete GainClone amplifier, including full chassis details (2 part article)2006PCB
116PWM Subwoofer Amplifier Using a ColdAmp BP4078 module, this article has complete construction details2006PCB
1171.5kW Power Amplifier Just the thing for those for whom no amount of power is enough grin2006 
118PC Power Switch Simplest ever PC switching unit - turn on peripherals with the PC2006 
119Signature Analyser A component signature analyser that allows in-circuit parts tests2006 
120 Crowbar Speaker ProtectionThe final answer to speaker protection.  Comes with many cautions and warnings!2007
121 Reading InductanceUse your DC voltmeter or frequency counter to measure crossover coils.2008
122 Ultra-Simple Mic PreampA single low cost IC and tiny PCB make a great utility microphone preamp.2008PCB
123 18dB/Octave Crossover A selection of 18dB/octave (3rd order) crossover filters.2009
124 Dummy LoadHigh power dummy load for amplifier testing.2009
125 4W-LRX4-Way Linkwitz Riley Crossover2009PCB
126 PWM DimmerPWM LED Dimmer/ Motor Speed Controller.2009PCB
127 TDA7293 AmplifierDual power amplifier, using the TDA7293 power opamp IC.2009PCB
128VU Meter Bridge Build a pair of VU meters to monitor your recording or PA level.2010PCB
129Matrix Mixer Now you can build a matrix mixer to suit your exact requirements.2010PCB
130 Inverse A-WeightingUndo the rolloff caused by the A-Weighting filter2010
131 Light Activated SwitchLittle to do with audio, but a useful project that can be adapted to other uses.  Includes sound activation (added Oct 2018)2010
132 Air Bearing TonearmMore of a proliferation of ideas and techniques than a "real" project, the vinyl lovers should look at this2010
133PA-PC Audio Interfaces Interfaces from the headphone output of a PC to PA mic input, and PA speaker line to PC recorder 2011
134 4mA Current Loop MicrophoneCommon for professional measurement microphones, but not well known outside the noise measurement field.2011
135 Phase Correlation MeterMore of an experimental circuit than anything else, it should help anyone trying to build a phase meter. (Published 2011)  2020
136 Hardware Based RTAA real-time audio analyser - contributed project, based on the multiple feedback bandpass filter described in Project 63.2011
137 Powered Box AmplifierComplete Preamp, crossover & power amps, designed for powered PA speakers, Leslie cabinets, 'party' systems, etc.  Set of 3 PCBs.2019PCB
138 Mains Under/ Over Voltage ProtectionSome equipment is vulnerable to under or over-voltage.  Use this protection unit to prevent damage (Aug 2012).  Now includes 3-phase detectors 2016
139 Mains Current MonitorA versatile, safe & accurate way to measure (and view with a 'scope) the current drawn by mains powered equipment2012
139a Simple Current MonitorMuch like P139 (versatile & safe), but a much simpler way to measure the current drawn by mains equipment2012
140 True RMS AdaptorThe only way to measure non-sinusoidal waveforms is true RMS or errors can be significant.  Use this adaptor to get true RMS readings 2012
141VCA Based Preamplifier If you need a multiple channel preamp with a single volume control for all, this might be just what you're looking for.  Ideal for home theatre! Uses the THAT2180 VCA. 2013PCB
142 Simple High Current RegulatorNeed higher than allowable input voltage or the need for more current than IC regulators can provide.  This basic design will be more than acceptable for many tasks.2013
143 Tone Burst Generator/ GateSometimes 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. 2013
144 Mains Power SequencerIf 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. 2013
145 Silent Guitar Effects SwitchingHow to use Vactrol® or DIY optocouplers to switch signals in guitar amplifiers.  No contact bounce or clicks, just virtually silent switching without any noises. 2013
146 Overload/ Clipping IndicatorOverload indicator for mixers, preamps or power amps.  Simple opamp comparator circuit gives fast response. 2013
147 BJT Muting SwitchA little known technique that doesn't look like it could ever work - using bipolar transistors. 2013
148 State Variable CrossoverPerfect for loudspeaker system development, or can be used as part of a biamped or triamped system.  12dB/octave continuously variable filters. 2014PCB
149 Musical Instrument Graphic EQGuitar, Bass or Keyboard Equaliser.  A greatly improved version of Project 64. 2014
150Wien Bridge based equaliser A functional building block that can be used in mixers, preamps, guitar and bass amps, etc. 2014
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. 2014
152-1Bass Guitar Amplifier (Part 1) First part of a project with the circuits for what might be one of the world's best DIY bass amps. 2015
152-2Bass Guitar Amplifier (Part 2) Part Two of the bass amp project describes the compressor, soft-clip and crossovers, and discusses power amp needs. 2015
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. 2014
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 2015
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. 2015
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 2015
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. 2015
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. 2015PCB
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. 2015
160LM386, LM380 & LM384 Power Amplifiers Sometimes, you only need a small amplifier to use as a signal tracer, or as a workshop monitor amp.  Nothing special, but useful. 2015
161High Impedance Input Stages This is a combination of a project and an article, so is listed as both.  When you need an input impedance of up to 1GΩ, this shows you how to get it. 2015
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 may be right, but some things are just too interesting to ignore. 2015
163Preamp Input Switching Using Relays How to use relays for input switching, including several designs for logic controls to allow push-button input selection 2016
164Signal Tracer 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. 2016
165Valve Tester for Service Techs If you service valve (tube) amplifiers, you need to be able to test output valves under the conditions used in the amp being fixed.  Note that it is not a 'general purpose tester. 2016
166Push-on, Push-off Mains Switch You can add a little 'bling' to your project with this simple design.  Instead of a toggle or rocker switch, you can use a momentary push-button to turn your gear on and off. 2016
167MOSFET 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.  2016
168Low Ohms Meter Most people don't need to be able to measure down to 10 milliohms or so, but sometimes there is a genuine need to do so.  This project shows how it's done. 2017
169Battery Powered Amplifier There seems to be some mystique about amplifiers that don't connect to the mains, and are therefore considered (at least by some) to be more 'pure'.  However, you don't need to shell out a fortune 2016
1706dB/ Octave Active Crossover Some people like the idea of 6dB crossover networks.  While first order networks provide little by way of driver isolation, there might be a few readers who'd like to experiment. 2016
171Infrasound Translator Infrasound (between 1Hz and 20Hz) is normally inaudible, but this project allows the sound to be heard using a voltage controlled oscillator to move the LF to the audible range   2017
172Wattmeter for AC Power Measurements For all service and development work, it's useful to know the current drawn by the system, and it's also now easy to measure the power consumed. (2019)2017
173Constant Directivity Horn Equalisation Constant directivity (CD) horns are unique amongst high frequency reproducers.  They need a 6dB/ octave boost for high frequencies, as provided by this project. 2017
174Ultra-Low Distortion Oscillator Ultra-Low Distortion Sinewave Oscillator, a contributed project with both exceptionally low distortion and lightning-fast settling time2017
175BTL Amp DC Protection Single Supply BTL (bridge tied load) amplifier speaker protection circuit, used when P33 cannot be used due to the amp's DC Offset.2017
176Fully Differential Amplifier P87A & B have been around for years, but sometimes you need the best possible common mode rejection ratio (CMRR).  This circuit does just that.2018
177Constant Current Transistor Tester Test transistors using constant collector (actually emitter) current.  Ideal for matching small signal and power transistors (Bipolar types only)2018
178Low Voltage Power Amplifier Techniques you can use to build a low-power, low voltage power amplifier.  Ideally, it should have much better performance than the common LM386 and its ilk2018
179Sinewave Oscillator A Filament Lamp Stabilised Wien Bridge Oscillator  2018
180Amplifier 'Power Meter' Add this meter to your power amplifier for some bling that (unlike most) is not simple 'eye candy', but actually shows how close you are to clipping   2018
181Accelerometer Audio Accelerometer For Speaker Box Testing (amongst other things)2018
182Pseudo-Random Noise Generator A maximum length sequence (MLS) noise generator with much better noise than a reverse-biased transistor junction (includes pink noise filter)2019
183Signal Detecting Audio Ducking Unit Ducking is a common application for PA systems, video production or anywhere you need to reduce the level of a background signal in the presence of speech2019
184Li-Ion Battery Cutoff Li-Ion batteries are ideal for many projects (especially test equipment), and this under voltage cutoff lets you ensure that the battery is not over-discharged if/ when you forget to turn it off 2019
185Polarity Tester Speaker, Microphone & Circuit Polarity Tester. Ideal for checking that everything in a system is properly phased to prevent sound anomalies. 2019
186Workbench Amplifier Single Chip 25 Watt/ 8 Ohm Workbench Power Amplifier.  Ideal for testing speakers, signal tracing, testing preamplifiers and a host of other uses. 2019PCB
187Moving Coil Head Amp Finally , a pair of moving coil head amplifier designs for MC phono cartridges.  Includes a discussion of noise and low noise circuitry. 2019
188Surround Sound Decoder (Mk. II) While Project 18 shows a surround sound decoder, this one is far more complete, and uses readily available PCBs supplied by ESP.  It's in operation, and works very well indeed. 2019PCB
189Audio Wattmeter Measure true power from an amplifier into a dummy load, or from an amplifier into a speaker.  Handles reactive loudspeaker loads and shows the actual power delivered. 2019
190Microphone Muting Circuit This simple project can be used to mute any microphone by the performer, including mics that are phantom powered. 2019
191Peak Voltage & Current Detector If you are unsure if your amplifier is way under or over-powered for your loudspeakers, this simple project can be used to monitor the peak voltage and current demanded while listening. 2019
19212V to ±12V Switchmode Supply If you use a single 12V DC wall supply, that's often not enough to run many projects.  This supply gives you ±12V from the single supply from the 'wall wart'   2019
19312V to P48 Phantom Power Supply Getting a suitable transformer for a P48 phantom supply isn't always easy, but this switchmode boost regulator can provide +48V from a single DC supply of 12-36V 2019
194Centre Channel Processor A Front Centre Channel Derived from the Pair of Signals of Conventional Stereo. This is a very interesting circuit, submitted by Peter Lehmann. 2019
195Guitar 'Talk Box' The guitar 'talk box' has been around for a long time, and it was made famous by many musicians in the 1970s.  It's still popular, and you can build your own. 2019
19612V Float-Charge Battery Supply This project is basically a 12V version of Project 98, and a 12V battery backup system is useful for electronic clock drives, or surveillance equipment. 2019
197Low Frequency Boost & High Pass Filter If you need to equalise a vented speaker enclosure, this low frequency boost and high pass filter circuit may be just what you need. 2019
198MOSFET Relay MOSFET relay using Si8751/2 MOSFET driver ICs.  Suitable for mains switching (with caveats) or for high voltage speaker protection where a relay will arc. 2019Pending
199ABC NYE EQ ABC New Years Eve Concert Equaliser (Specific To Australia, but ...)  End the muffled sound broadcast by the ABC! 2020
200DIY LDR Optocoupler Build your own 'Vactrol' using a LED and LDR (light dependent resistor).  This has been 'transplanted' from an article where it was shown as part of construction project. 2020
201Multi-Channel Trailing-Edge Dimmer This project came about from the MOSFET relay (P198) and is suitable for use in the Project 62 'LX-800' dimmer, or used as a stand-alone system. 2020
202Piezo Preamplifiers Piezo guitar/ violin/ double bass etc. pickups are common, and here are a few options.  Includes one of the lesser known types - a charge amplifier (includes ceramic phono cartridges).   2020
203Guitar/ Studio Spring Reverb Unit A complete spring reverb sub-system for guitar, keyboards or studio use.  Possibly the most complete reverb system currently available   2020Pending
204Frequency Shifter Used for acoustic feedback reduction.  There's a choice of two circuits, one being an updated version of the first published frequency shifter, plus a high-performance version.   2020Pending
2054-Channel Mixer For Microphones Or Instruments.  It's built using existing ESP boards (other than the clipping indicator which will be available at a later date)   2020PCB
ABXABX Comparator Full ABX testing unit, without microcontrollers or a PC
XA-B Switch Box Can you really hear the difference between amps or cables?

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!

Not all projects that involve mains wiring are so marked, because some mains wiring is required in most projects that include a power supply.  Appropriate warnings are generally placed within the article itself, and it is the reader's responsibility to ensure that all regulations that apply where you live are adhered to.  I cannot provide detailed information for each country, so you need to know the regulations, colour codes and any other requirements as necessary to ensure safety.


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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 - 2019 (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.