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Last Updated: June 02, 2021 01:44 PM

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I.R. Headphone SystE - M -  The 555 forms on oscillator generating pulses at a frequency of about 100kHz.  Pin 5 on the 555 is the "control voltage" pin.  A voltage applied to this pin will vary the frequency of the oscillations.  If the input is an audio frequency alternating voltage, it will modulate the frequency of the oscillator.  We therefore have a frequency modulated (f.  m.) infra-red beam. __ Designed by © David Hoult

Infrared Audio Headphone Link for TV -  Do you have trouble understanding what's being said on the TV? Do you need the volume cranked up too loud for everyone else? Do you have a hearing aid as well? If you said yes to any other these questions, here is your answer: an infrared transmitter and receiver to let you listen to the TV sound via headphones.  That way, you can listen as loudly as you like, without disturbing anyone else.__ SiliconChip

Infrared cordless Headphone Amplifier -  Using this low cost Project one can reproduce AUDIO from TV without disturbing anyone.  It does not use any wire between TV and HEADPHONE.  In place of pair of wires it uses invisible Infrared light to transmit audio signals from TV to Headphone.  Without using any lens a range of up to 6 meters is possible.  Range can be extended by using Lenses and Reflectors with IR sensors comprising transmitters and receivers.  IR transmitter uses two-stage transistor amplifier to drive two IR LEDs connected in series. __ Designed by YMYA electronics-IZHAR FAREED

Infrared Theremin Musical Instrument -  The constituents of the electronic circuitry in the invention are represented in the following figure, "Block Diagram of the Optical Theremin.  " Note that the interconnecting lines and arrows in the figure are representative of the signal process sequence, and not representative of specific electrical connections __ Designed by Arthur Harrison

Light Organ for Car -  flashes3 low voltage Light, operates at10-25-Volt voltage, in PDF format, text in Finnish|

Line level Signal to microphone input adapter -  Sometimes there is need to convert line level signals to such signal that it can be connected to microphone input.  Because the line level signals are typically in range of 0.5.2V and the microphone signals are in millivolt range, quite much attenuation is needed to match the signal levels.  This means that typically you will need 40-50 dB of attenuation __ Designed by Tomi Engdahl

Linkwitz Cosine Burst Generator -  Based on work done by Siegfried Linkwitz (reproduced with his permission) __ Designed by Rod Elliott  ESP

LM358 preamp -  Another very simple audio preamp to build.  all parts should be available at your very local electronics shop. __ Designed by Andy Wilson

Loud Speaker Protection & Muting -  Protect speakers from turn-on and turn-off transients and amplifier faults __ Designed by Rod Elliott  ESP

Loudspeaker Test Box -  Quickly and accurately determine the optimal impedance correction network __ Designed by Rod Elliott  ESP

Low Frequency Sine Wave Generator -  The two circuits below illustrate generating low frequency sine waves by shifting the phase of the signal through an RC network so that oscillation occurs where the total phase shift is360 degrees. __ Designed by Bill Bowden

Low Noise Balanced Microphone Preamp -  A discrete front end makes this balanced microphone preamp very quiet __ Designed by Rod Elliott  ESP

Low Noise Microphone PreAmplifier -  This is a design for a low noise microphone preamplifier, which is ideally suited to low impedance (600 Ohm nominal) microphones.  One limitation is that it is not balanced, which is not a problem in a home recording environment, but will allow the mic lead (and case) to pick up noise with long cable runs or in a hostile environment. __ Designed by Rod Elliott  ESP

Low Power Op-Amp-Audio Amp Intercom -  The example below illustrates using an op-amp as an audio amplifier for a simple intercom.  A small 8 ohm speaker is used as a microphone which is coupled to the op-amp input through a 0.1uF capacitor.  The speaker is sensitive to low frequencies and the small value capacitor serves to attenuate the lower tones and produce a better overall response.  You can experiment with different value capacitors to improve the response for various speakers.  The op-amp voltage gain is determined by the ratio of the feedback resistor to the series input resistor which is around one thousand in this case __ Designed by Bill Bowden

Magnetic Cartridge Amplifier -  Schematic Only __ Designed by Andy Wilson

Mains 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

Making Differential Probes -  For sensing audio signal voltages across devices that are not ground referenced__ Liberty Instruments, Inc

Making Your Own HeadBanger -  After the euphoria over receiving my new Sony Minidisc bundle had partially subsided, I noticed that the portable unit, the MZ-E40, has a rather weak output.  Measurements showed that it can only manage 80mV rms output and only about 74dB SPL output from the phones.  This is when recording at average level with 8dB of headroom.  In contrast, an orchestra__ Stephen H. Lafferty

Microphone from a Speaker -  A circuit to Impedance Match a Speaker as a Mike.    Speakers can make a Good Microphone for some applications.    Bigger Speakers may also have a Good Low Frequency Response.     Ever seen a 15 Inch Microphonethis Circuit will do it __ Designed by G.L. Chemelec

Microphone Mixer -  Designed for 3-dynamic microphonesThis relatively simple mixer was designed for three dynamic microphones, but can be re-designed for more or less.  Level and tone controls are available to tailor the sound to your needs. __ Designed by Aaron Cake

Microphone phantom power supply -  This is a very simple design for a phantom supply.  This design will work with microphones that have no problem with the phantom supply being only 15V.  It also has to be noted that, at high SPL, distortion can become intolerable (totally depending on microphone design).  In that case, the phantom supply voltage has to be increased.__ NewLine

Microphone Test Oscillator -  This unit would be mounted in a small plastic or preferably metal box, with a 9V battery, level control, a male XLR connector (same as on a mic) and a switch.  Current drain is low, since the circuit only uses one dual opamp.  There is no need for a high quality device, and a 1458 (or 4558 which is somewhat better but still cheap) is all that is needed __ Designed by Rod Elliott  ESP

Midibox 64 -  Schematic Only|

MIDITester -  Sometimes when experimenting with different soundcards and MIDI interfaces it is useful to see if there is some data going in MIDI interface.  This can be easily tested with this adapter, which converts the midi signals to visible light pulses.  Just the circuit and plug it to the MIDI output of your computer.  When computer sends any midi data out, you see the LED flashing.  I found this tester very useful in testing homebuilt soundcard MIDI interface. __ Designed by Tomi Engdahl

mini Theremin Mk.2; Pt 2 -  Last month, we described the features of our new Theremin and gave the full circuit details.  This month, we show you how to build it and describe the adjustment procedures.__ SiliconChip

Mini Theremin Mk.2; Pt.1 -  Just move your fingers near the antennas of this theremin to create your own electronic music or eerie science fiction sounds.  It's easy to build, easy to set up and easy to play.__ SiliconChip

Mini-Box 2 Watt Amplifier -  This amplifier was designed to be self-contained in a small loudspeaker box.  It can be feed by Walkman, Mini-Disc, iPod and CD players, computers and similar devices fitted with line or headphone output.  Of course, in most cases you will have to make two boxes to obtain stereo __ Contact: Flavio Dellepiane, fladello @ tin.it

Minimalist Discrete Hi-Fi Preamp -  Note that the project described here has been superceeded by the new Revision A version.  The new circuit uses a dual supply, and does not include the power supply.  P05 is ideally suited for this new version.  A preamp designed for the minimalist, and having no frills at all is the design goal for this project.  It is designed as a preamp for the Death of Zen (DoZ) Class-A power amp (Project 36), and has very low levels of noise and distortion, in a minimum component count, fully discrete circuit. __ Designed by Rod Elliott  ESP

Minimum Theremin Kit Schematic -  Two identical integrated circuits, U1 and U2, known as "hex inverters" are used for the theremin's primary functions.  They are CMOS (Complimentary Symmetry Metal Oxide Semiconductor) devices, typically used in digital circuits to perform a logic function called "inversion.  " Each IC contains six identical sections; thus the term "hex inverter.  "

Modular Headphone Amplifier -  140mW into 32 Ohm loads; Ultra-low Distortion __ Contact: Flavio Dellepiane, fladello @ tin.it

New, Improved Theremin Mk.2 -  This design is an upgrade of our most popular Theremin which was featured in the August 2000 issue.  We have added a voicing control, incorporated a larger loudspeaker and increased the power output.  We've also changed the power supply to avoid problems with switchmode DC plugpacks.__ SiliconChip

One 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!|

Parametric & Sub-Woofer Equaliser -  The unit is simple to build, and does not need really low noise opamps, since they only act as a modulator oscillator.  I used 1458 dual types in the prototype, and they are more than good enough.  The transistors can be any low noise NPN type, and they are simply buffers, ensuring a high input impedance and low output impedance.  You can use opamps as buffers instead of the transistors Q1 & Q2 if you prefer.  A single TL072 with both halves wired as unity-gain non-inverting buffers will work fine, and may allow you to eliminate C1, C2 and C3. __ Designed by Rod Elliott  ESP

Peak Level Indicator -  Dot-mode three-LED display.9V battery powered portable unit __ Contact: Flavio Dellepiane, fladello @ tin.it

Peak Reading Audio Level Meter -  indicates peak audio response on an analogue meter, similar to a tape recorder recording level meter __ Designed by Andy Collison

Phono Preamps for All -  Various circuits for moving coil and moving magnet pickups __ Designed by Rod Elliott  ESP

Portable E-field Receiver -  Here is a tiny receiver built into an Altoids tin suitable for use with a laptop computer or portable tape recorder.  The prototype antenna is only 1 foot long when fully extended and the receiver fits into a shirt pocket __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Portable Headphone Amp -  Another contributed circuit, this is a complete portable headphone amp that features crossfeed. __ Designed by Rod Elliott  ESP

Portable Headphone Amplifier -  3V Battery powered High Performance unit __ Contact: Flavio Dellepiane, fladello @ tin.it

Portable Headphone Amplifier for MP3 Players -  Fixing Transformer Buzz In The Class-A Amplifier__ SiliconChip

Precision Audio MilliVoltmeter -  Measures10mV to 50Volt RMS in eight ranges Simply connect to your Avo-meter setAT 50µA range __ Contact: Flavio Dellepiane, fladello @ tin.it

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