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Last Updated: June 02, 2021 01:44 PM

Links to electronic circuits, electronic schematics and designs for engineers, hobbyists, students & inventors:

"NuHybrid" headphone amp -  A low-voltage hybrid headphone amp using the Korg Nutube 6P1 __ Designed by Pete Millett

1 Transistor Theremin -  This design is from a magazine called "Divirta-se com a Eletrônica", which translates to "have fun with electronics", and, indeed, is very fun.  For those who don't know what a Theremin is, it's one of the first synths ever made and it's named after his inventor, Mr.  Leon Theremin   (a Russian guy).  It's perhaps the only instrument which you don't actually touch: there's an antenna, and as the musician moves his hand near it, the pitch changes.  That's the thing Page used in "Whole Lotta Love"   (he used it with an echo, to get even weirder).  This circuit is a very simplified version of a theremin, but is also very easy to build and really works!|

1.5V Headphone Amplifier -  This circuit stabilizes the quiescent voltage across the speaker at the exact level necessary to get the desired maximum available volume at minimum battery draw.  This more than doubles the battery life compared to just connecting a simple resistor betwee __ Designed by Andrew R. Morris

2 Input Mixer -  Sometimes there is need to combine the output of two line level audio sources to be fed to one input.  A standard way in professional audio is to use a mixing desk, but on home audio system you might want to look for a simpler and less expensive alternative.  Some people have suggested of combining two audio outputs with an "Y-adapter" which is ment to split one output.  Those adapters are just one male connector and two feamle connector directly wired to each other in the followin way: __ Designed by Tomi Engdahl

24 dB/Octave 2/3-Way Linkwitz-Riley electronic crossover -  Linkwitz-Riley alignment.  This is a very nice crossover, Rev-B boards now available __ Designed by Rod Elliott  ESP

2-Way Electronic Crossover -  Conventional 3rd order electronic crossover __ Designed by Rod Elliott  ESP

2X12 W HiFi Amplifier by TD2616 -  Here is the circuit of a 2X12 watt HiFi amplifier circuit using IC TDA 2616 from Phillips.  A quiet simple and robust circuit using very less components.  This makes the circuit ideal for a portable power amplifier.  The circuit delivers 12 W power on 8 Ohm speaker for each channel at +/- 12 V dual supply|

3 Channel-Color Organ -  An old ideabut I've had numerous requests for a good design for this __ Designed by G.L. Chemelec

3 Level Audio Power Indicator -  Battery-operated3 LED display that connect it to loudspeaker output __ Contact: Flavio Dellepiane, fladello @ tin.it

300 Watt Subwoofer Power Amplifier -  There are some important updates to this project, as shown below.  Recent testing has shown that with the new ON Semi transistors it is possible to obtain a lot more power than previously.  The original design was very conservative, and was initially intended to use 2SA1492 and 2SC3856 transistors   (rated at 130W)with 200W   (or 230W) devices, some of the original comments and warnings have been amended to suit. __ Designed by Rod Elliott  ESP

3-Way 12dB/ Octave Crossover -  Contributed project, simple 12dB/ Octave crossover network. __ Designed by Rod Elliott  ESP

4 Channel CAR Color Organ -  Back in the 1970's these were popular for use in homes and the colored bulbs were typically place in a box with a sheet of "rippled/bubbled" Plastic in front to break up the light patterns.  Some units gave very impressive light patterns. __ Designed by G.L. Chemelec

48V Phantom Supply -  Low noise 48V regulator and phantom mic supply circuits __ Designed by Rod Elliott  ESP

555-based class-D headphone driver makes great practice Amp -  07/28/14  EDN-Design Ideas This class-D audio amp “plays” to the 555’s strengths.  Design by Petre Petrov

7 band graphic eqalizer -  Audio graphic equalizers are very common as commercial products (for Hi-fi, car audio and stage use) but circuits for them are very rarely published.  I didn't design this one but it's really very simple.  The details shown are for a 7 band but the principle can be extended to almost any number of bandsif you can find accurate enough components. __ Designed by Richard Torrens

A Musical Distortion Primer -  This is an introduction to the basic means of distorting a signal in a musically useful way.  The approach is as non-technical as possible.    I use the simplest signal waveform, a sine wave, to illustrate all these, although a guitar is much more like a sawtooth than a sine wave.  The clipped waveforms will be shown in their raw state __ Designed by R.G. Keen

A Reader's Xover -  This is well worth reading if you can't decide on biamping __ Designed by J. L. Linsley Hood, M.I.E.E.

A Weighting Filter for Audio Measurements -  For noise measurements.  Ideal for use with the AC Millivoltmeter above __ Designed by Rod Elliott  ESP

A-B Switch Box -  Can you really hear the difference between amps or cables? __ Designed by Rod Elliott  ESP

ABX Comparator -  Full ABX testing unit, without microcontrollers or a PC __ Designed by Rod Elliott  ESP

AC Power Line Power Load Sensing Automatic Switch -  WARNING:  This circuit requires experience with mains wiring.  Do not attempt construction unless experienced and capable.  Death or serious injury may result from incorrect wiring. __ Designed by Rod Elliott  ESP

Active Subwoofer & Controller -  Designed to operate a sub-woofer driver below its resonant frequency __ Designed by Rod Elliott  ESP

Add Headphones to a Class D Amplifier -  9-Jul-09 EDN-Design Ideas Connect headphones to the MAX9704 and make a quieter lab or office Design by Hiroshi Fukushima, Technical Research Center, D&M Holdings Inc, Kawasaki City, Kanagawa, Japan

Add on Stereo Channel Selector -  The add-on circuit presented here is useful for stereo systems.  This circuit has provision for connecting stereo outputs from four different sources/channels as inputs and only one of them is selected/ connected to the output at any one time __ Designed by PRABHASH K.P.

Amplifier Thermal Protection -  The thermal protection of amplifiers is always a concern, since overheating is a sure way to reduce the life of semiconductors and other components.    Where you don't want to use a fan   (such as in Project 42Thermo-Fan for Amplifier Cooling), then a complete shutdown can be performed. __ Designed by Rod Elliott  ESP

Arc welder sound simulator -  Detailed workshops and maintenance yards can be the highlight of many model railways or dioramas.  Unfortunately they usually suffer from one common problem.  They are static.  At the scale involved, it is not an easy problem to overcome either.  Moving parts at this size present quite a challenge __ Designed by Collin Mitchell

Atmega48/88/168 Development Board -  This is versatile development board for AVR microcontrollers ATmega48/88/168.  It is good for testing and debugging embedded programs.  It has many built-in peripheries connected to microcontroller __ Designed by Radio LocMan

Audio Activated Recorder -  ScanMate connects between your scanner and tape recorders (via the recorder's microphone or auxiliary input and its remote start jack). __ Designed by Tony van Roon  VA3AVR

Audio Amp Output Power Limiter -  If you hire out audio equipment, or just don't want the kids to blow up your speakers when you are not home, this is the project for you.  It is a very simple little project, but will protect the speakers from being overdriven.  Any attempt at overdrive will simply cut the amp gain backthe more overdrive, the more the input signal is reduced. __ Designed by Rod Elliott  ESP

Audio Amp Timer -  Turns-off your amplifier when idle for15 minutes Fed by amplifier tape-output __ Contact: Flavio Dellepiane, fladello @ tin.it

Audio Amplifier Output Relay Delay -  This is a simple circuit which I built to one of my audio amplifier projects to control  speaker output relay.  The purpose of this circuit is to control  relay which turns on  speaker output relay in  audio amplifier.  The idea of  circuit is wait around 5 seconds after  power up until  speakers are switched to  amplifiers __ Designed by Tomi Engdahl

Audio Detector -  Someone asked, a couple weeks ago, for a circuit to do audio detection. 
This is what I used.  Here is one that uses a single IC   (LM324 quad op amp)
and a handful of parts.  This circuit is for detecting one of those 3.6khz
  (approx) beepers from Radio Shack. __ Designed by Larry Barello

Audio Graphic Equaliser -  Audio graphic equalizers are very common as commercial products (for Hi-fi, car audio and stage use) but circuits for them are very rarely published.  I didn't design this one but it's really very simple.  The details shown are for a 7 band but the principle can be extended to almost any number of bandsif you can find accurate enough components. __ Designed by Richard Torrens

Audio Level Meter -  Audio levels can be monitored using a small panel meter with this circuit built from discrete components.  The circuit has a flat frequency response from about 20Hz to well over 50Khz.  Input sensitivity is 100mV for a full scale deflection on a 100uA meter.  Built on two common emitter amplifiers, the first stage has a preset resistor which may be adjusted for a FSD.  The last stage is biased to operate at roughly half the supply voltage for maximum ac voltage swing.  Audio frequencies are passed through the 10u dc blocking capacitor and the full wave bridge rectifier converts the signal to a varying dc voltage __ Designed by Andy Collison

Audio line isolator -  If you want to do the ground loop elimination in audio path, you have to cut the galvanic connection but pass the whole audio range.  The simplest and most common way to do the isolation is use audio transformer which is ment for audio use.  Transformers for audio use have some problems like distorted bass response and attenuating in high-frequency response.  Basically a transformer slows down upper frequencies and allow the low frequencies to pass first, creating what we perceive as a "fat/warm" tone. __ Designed by Tomi Engdahl

Audio Peak Reading Meters -  Peak reading meters, popular in Europe for years, are just now coming into greater favor in America, and for good reason.  The main purpose for having a VU meter is obviously to monitor signal levels going to a tape recorder, reverb unit, or some other level-sensitive device, to help optimize the signal to noise ratio of the audio sent to the device.  Too much level will produce distortion, and too little results in the inherent noise of the medium becoming a problem.  Unfortunately, a conventional VU meter responds to the average level of the program material and not to the peaks; yet it is these momentary bursts of higher level that become distorted first. __ Designed by Ethan Winer-This article first appeared in the April 1981 issue of Recording-engineer/producer magazine.

Audio Signal Source -  This is a lovely project for home constructors keen on building their own test and measurement   (T&M) equipment.  It makes use of the ICL8038 signal generator chip, manufactured by Intersil.  An improved version, made by Exar corp.  is available   (XR8038A).  It can be used to produce three types of waveforms, sine, square and triangle.  The frequency, amplitude and duty cycle can be varied, and selection of waveform is done digitally. __ Designed by Tony and Wilfred of Mixed Fruit Jam

Audio Speech Processor -  Although most modern HF rigs have built in speech processors, a lot of the low power SSB rigs and kits do not have any real speech processor circuitry.  When one operates at low power on SSB, speech processing becomes almost essential to get through the QRM.  The circuit in figure 1 is a low cost speech processor that will perform well with a minimum of construction effort.  The circuit even includes the microphone element so that a complete speech processor microphone can be assembled in an old defunct desk mike __ Designed by Radio Amateur Society of Norwich

Audio Sweep Oscilator -  This circuit was designed for a sound effect, but may serve other useful purposes when a basic, swept-frequency audio source is required.  It produces both square and triangular wave outputs that ascend from about 80 to 730 Hertz in a repeating cycle of about 12 seconds.  Appropriate component-value substitutions will yield variations in these parameters.  Operation is as follows:Operational amplifier U2B and its associated components form an astable multivibrator with __ Designed by Arthur Harrison

Audio Test Oscillator -  As a piece of test equipment, an audio oscillator has to be considered essential for anyone working in with hi-fi gear.  Together with an audio millivoltmeter   (as described in Project 16) , and even better if you have access to an oscilloscope, you will be able to make proper measurements on everything from preamps, RIAA equalisation stages   (for vinyl disks) , tone controls, crossover networks, etc __ Designed by Rod Elliott  ESP

Audio Voice-Over -  This is a circuit where a microphone and preamp circuit   (voice circuit) have priority over any other audio signal.  You can think of this as a one way intercom, if the main amplifier is used for listening to music, then when the push to talk switch is pressed, the amplifier is switched to the voice signal. __ Designed by Andy Collinson

Audio VU Meter -  LM324, This circuit uses two quad op-amps to form an eight LED audio level meter.  The op-amp used in this particular circuit is the LM324 __ Designed by Matthew Hewson

Audio-test accessory isolates & matches loads -  03/16/06  EDN-Design Ideas This low-cost, switchable, dual-impedance transformation circuit comprises a single conventional transformer and two minimum-loss pads Design by Richard M Kurzrok, RMK Consultants, Queens Village, NY

Auto volume control -  Schematic only, no circuit description included __ Contact: IQ Technologies

Automatic Charger for Battery Operated Hi-Fi Preamps -  For those who want the cleanest possible DC for sensitive preamps, battery power is ideal.  At last, remembering to turn the charger back on is no longer a problem!  This project is one for the experimenter, but as shown will work extremely well.  The sensing circuit can be made so sensitive that a load of only 2.5mA is enough for the circuit to detect, and disconnect the charger. __ Designed by Rod Elliott  ESP

Automatic Loudness Control -  Simple add-on module Switchable "Control-flat" option __ Contact: Flavio Dellepiane, fladello @ tin.it

Audio Accessories:   #-A       B - D       E - H       I - P        R - S       T - Z

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