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Amplifiers: Audio Circuits
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Last Updated: June 02, 2021 01:44 PM

Circuits Designed by Dave Johnson, P.E. :
Improve the quality of standard TV images  -  I designed this circuit many years ago, based on the claims that the technique would improve the quality of standard TV images.  The circuit adds information to the edges of the objects and was reported to bring out more detail.  After building and testing . . . Hobby Circuit designed by David A. Johnson P.E.-July 08, 2000

Infrared TV/VCR Remote Booster  -  This circuit will boost the signal from any infrared TV or VCR remote, extending the range by a factor of 3X.   . . . Circuit by Dave Johnson P.E.-October 05, 2005

IR TV/VCR Remote Booster  -  This circuit will boost the signal from any infrared TV or VCR remote, extending the range by a factor of 3X.   . . . Hobby Circuit designed by David Johnson P.E.-October 05, 2005

Low Pass Filter, 3Khz, with an Audio Amp  -  This circuit uses a switched capacitor filter IC from National Semiconductor to filter signals with frequencies higher than the 3KHz needed for voice audio.  The schematic includes an audio amplifier that is designed to drive a standard audio head phone . . . Hobby Circuit designed by Dave Johnson P.E.-June 04, 2000

Microphone On/Off Switch Circuit is Pop Free  -  This circuit uses a simple technique to eliminate the usual “pop” sound when an electret type microphone is switched on or off.  The circuit is completely passive and will work on dynamic and electret type microphones . . . Hobby Circuit designed by Dave Johnson P.E.-February 15, 2002

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

Echo Tone Oscillator -  This simple circuit amplitude-modulates a single tone in such a manner to approximate the echo effect one might obtain, for instance, with sonar apparatus.  Any reader who has been on a sonar-equipped vessel will realize that some imagination is required to appreciate the similarities among this simple scheme and the "real thing.  " However, this circuit might adjunct a small model (of a submarine, perhaps) to add the dimension of sound __ Designed by Arthur Harrison

ECM Mic Preamplifier -  A microphone amplifier that may be used with either Electret Condenser Microphone (ECM) inserts or dynamic inserts, made with discrete components. __ Designed by Andy Collison

Eight-watt Audio Amp -  Here is the schematic for an 8 watt audio amp.  This amp can be used as a simple booster, the heart of a more complicated amplifier or used as a guitar amp. __ Designed by Aaron Cake

Electret mic Amplifier -  The Elecraft XG2 is a crystal oscillator with accurate 1 µV and 50 µV output levels.  It's ideal for receiver test and alignment.  The 1-µV output can be used to measure a receiver's sensitivity, while the 50-µV output is useful for S-meter calibration.  Switch-selected output frequencies of 3579, 7040, and 14060 kHz provide convenient test signals on 80, 40, and 20 meters; harmonics of these frequencies can be used for measurements on higher bands __ Designed by Andy Wilson

Electret Microphone Connection -  how to connect electret microphone __ Designed by Tomi Engdahl

Electret Microphone Powering -  This document is a collection of information and circuits for powering electret microphone capsules.  This document is written for people who understand the basics of microhone circuits. __ Designed by Tomi Engdahl

Electrete Condenser Microphone Line Level Preamplifer Powered by USB  -  This preamp lets a condenser microphone work with line level inputs such as those found on Macintosh computers. __ Designed by Dick Cappels

Electric Guitar Preamplifier -  This is a circuit for a guitar preamplifier that can capture mechanical vibrations (any standard guitar pickup) and then convert them into an electrical signal.  The signal is then amplified by an audio amplifier. __ Electronics Projects for You

ElectricPickup -  I have an unused 900 MHz antenna sticking out of my chimney that has an ungrounded vertical element.  I replaced the 12 inch element with a two yard aluminum rod (see photo).  The antenna isonly 75 feet from the power lines so I didn't have much hope for this antenna to work.  The lead-in coax is long so its capacitance (about 1, 500 pF) forms a voltage divider with the capacitance of the antenna so the signal is significantly __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Electronic attenuator -  This electronic astrologer answers in either YES or NO.  For this reason it is a good idea to put this circuit in a box, and mark one LED as YES, and another as NO.  Electronic astrologer can played like this :- You ask such question whose answer can be either YES or NO, e.g Is it going to rain today ?.  Now, press and release push-button(S1) to get the answer.  After release, the glowing LED is electronic astrologer's answer.

Electronic Bicycle Horn -  This simple electronic bicycle horn circuit uses only one gate of a 4093 quad 2-input NAND Schmitt trigger, U1, conected in a simple, low frequency, square-wave oscillator circuit.  The oscillator’s output, at pin 3, drives the gate of Q1.  The drain of that FET drives a small horn speaker.  Potentiometer R1 can be adjusted __ Designed by D Mohankumar

Electronic Canary Sound Effects -  An electronic version of a chirping canary.  May be used as an alarm, a sound effects generator or perhaps a replacement doorbell __ Designed by Andy Collinson

Electronic Church Bell Controller -  This circuit is a church bell controller.  Basic component is an ATmega32 microcontroller.  At the circuit 2 24LC32 eeprom memories is being used, the 1st for internal standard melodies and the 2nd one is for user's compositions.  This feature will be provided in the future __ Designed by Antonis Pontikakis © 03.10.2007

Electronic Metronome -  A metronome is used by musicians for practice in maintaining a consistent tempo, or rubato, around a fixed beat.  This circuit produces a regular beat at the rate of 40 to __ Electronics Projects for You

Electronic Metronome -  A Universal Power supply based on the L200 regulator, which includes an outboard pass transistor to boost output currents up to 4 amps. __ Designed by Volker Jeschkeit

Electronic Metronome with 555 -  This metronome circuit is not modern but is cheap and reliable.  The well known 555 is connected as an astable multivibrator in this electronic metronome and produces a regular train of impulses which can be heard with a speaker.  The metronome frequency can be adjusted with P1.  The power supply is a 9V battery and if you use a __ Designed by Popescu Marian

Electronics attenuator -  Two low voltage, low power zeners are used to control electronically the level of an audio signal.  The attenuation range is from 6 to 58dB for an input current from 0.042 to 77 mA corresponding to a control voltage from 2.7 to 7.5V.  If control voltage is limited to 5V, the attenuation is around 30dB at a control current of 2mA.  This is not an HiFi attenuator but might come useful as a general purpose audio attenuator. __ Contact: IQ Technologies

Emulate Mechanical Metronome -  08/19/99 EDN-Design Ideas The circuit in Figure 1 produces timing signals with a sound like that of a mechanical metronome. IC 1 is a 555 timer that oscillates at approximately 3200 Hz.  The two 3-kW resistors and the 0.047-µF capacitor set the frequency. IC 2 divIdeas the frequency of IC 1 's output by 2. IC 2 produces a square wave with an exact 50% duty cycle. Design by Jim Kocsis

Envelope generator ADSR -  This envelope generator is based on a classical monostable configuration of the 555.  I improved this circuit and I provided two versions, the old one and a new improved one. __ Designed by Örley Gŕbor

ESP SIM Sound Impairment Monitor -  The smallest variation in amplifier performance is shown with this simple circuit __ Designed by Rod Elliott  ESP

Faraday’s Guitar -  Experimenting with the fundamentals of electrical and electronics is always interesting.  Presented here is an electronic circuit that demonstrates Faraday’s law of electromagnetic induction and gives musical output.  The law talks __ Electronics Projects for You

Fast Audio Peak Limiter -  This peak limiter is simple and very effective.    Uses discrete FET gain control __ Designed by Rod Elliott  ESP

Faux-phaser with LFO & manual (wah pedal) Modes. Schematic & & PCB layout. -  The original Phozer was a sound idea, but was hindered by its mashed-up development.  The circuit didn't really exceed the sum of its parts, namely Tim Escobedo's Idiot Wah and the LFO from the EA Tremolo.  The faux phase shifting effect was reasonably convincing at faster speeds, but the LFO failed to produce a true sweep at slower speeds.  Rather than ramp up and down, at slow speeds the LFO simply spent more time in the darker heel-down position between quick pulses of toe-down mode.  Also, we saw that using op-amps rather than discrete components would probably allow for a more complex effect with fewer parts. __ Contact: holler @ runoffgroove.Com

Fender Princeton adapted for use as a distortion stompbox -  One of the often overlooked Fender amps is the tweed-era Princeton.  They are excellent guitar amps, especially for blues playing.  The major drawback was the 4.5 watt output wasn't enough to keep up with a band.  Again, using the technique pioneered by Doug Hammond, we decided to try to capture some of the sound of this little amp in pedal form so it can be used with a band. __ Contact: holler @ runoffgroove.Com

FET Audio Mixer This simple circuit mixes two or more channels into one channel   (eg.  stereo into mono).  The circuit can mix as many or as few channels as you like and consumes very little power.  The mixer is shown with two inputs, but you can add as many as you want by just duplicating the "sections" which are clearly visible on the schematic. __ Designed by Aaron Cake

FET Preamplifier -  Field Effect Transistor is an amplifying device in which the output current depends on the input voltage.  The FET Pre Amplifier described here is a sensitive and stable Preamp circuit using an N-Channel FET and a PNP Bipolar transistor.  This combination gives high input impedance and low output impedance with stabilized gain. __ Designed by D Mohankumar

Fetzer Valve -  In the two years since the Fetzer Valve was first published in the midst of our adaptation of tube amps for use as distortion pedals, the circuit has enjoyed popularity as a standalone booster and as a building block in larger circuits.  While the circuit has its merits, we decided to further explore it to determine if it was a truly faithful solid-state version of the familiar input stage used in many tube amps. __ Contact: holler @ runoffgroove.Com

Filter-Active High Pass -  active filter sallen key design.  Ideal for tone controls, tweeter/midrange drivers and demodulating __ Contact: P. Townshend EduTek Ltd

Fitting a Wireless Microphone to the PortaPAL -  Here's how to fit a pro-quality wireless mic to the PortaPAL to make it truly portable. __ SiliconChip

Five band graphic equalizer -  This circuit uses a single chip, IC BA3812L for realizing a 5 band graphic equalizer for use in hi-fi audio systems.  The BA3812L is a five-point graphic equalizer that has all the required functions integrated onto one IC.  The IC is comprised of the five tone control circuits and input and output buffer amplifiers.  The BA3812L features low distortion, .  

Five-Band Graphic Equalizer -  This complete high quality, low noise 5-BAND GRAPHIC EQUALIZER circuit is based around Monolithic Linear integrated circuit LA3600 manufactured by SANYO.  This circuit is very easy to build and has good Quality.  You can use it with Portable component stereos, tape-recorders, radio-cassette recorders, car stereos etc
It is On-chip one operational amplifier. __ Designed by YMYA electronics-IZHAR FAREED

Flipster -  When one thinks of classic bass amps, the brand name "Ampeg" often comes to mind.  Their SVT models were very popular and still are today.  Slightly less known Ampeg combo-type models were also made, called "Portaflex" amps.  In "travel" form, these appeared to be simple closed back speaker cabs with a pair of chrome latches on either side of the top panel.  When one released the latches, the top panel could be removed and flipped over to reveal a tube head unit.  One simply plugged in the attached speaker cable and the amp was ready to go.  The unique design led to the nickname of "Flip Tops." __ Contact: holler @ runoffgroove.Com

FM Bug -  This FM bug transmitter circuit will let you spy on people.  The transmitter can be placed in the desired room and the conversation heard from a place far away just using __ Electronics Projects for You

FM Microphone -  A micro-transmitter is so small and sensitive, it have only 8 easy-to-get parts and can be assembled in one hour. __ Designed by Jose Pino

FM Radio Microphone with Internal Loop Antenna (Area 50) -  This article began as a design guide for hyper cranial erogenic field generators, however, your primitive earth brains are completely unable to respond to erogenic fields in the 100MHz region.  I personally had a brain upgrade (for purely medical purposes of course) so I am able to respond __ Contact: Charles Wenzel of Wenzel Associates, Inc.

FM transmitter for MP3 & MP4 Player, computer, Mobile Phone-high power transistor 2n2218 & 741 opamp -  Evolution FM transmitter with 2n2218 with audio amplification step using LM741 op amp with audio input for MP3, MP4, mobile, computer and other audio sources, beyond the traditional electret microphone.  With great sensitivity to the input signal.  Using fewer components and easy assembly makes it ideal for those who want even without much experience assembling __ Designed by Antonio Rodrigues

FM Transmitter-Miniature -  This miniature transmitter is easy to construct and it's transmissions can be picked up on any standard FM receiver.  It has a range of up to 1/4 of a mile or more.  It is great for room monitoring, baby listening, nature research, etc.  L1 is 8 to 10 turns of 22 gauge hookup wire close wound around a non-conductive 1/4 inch diameter form __ Designed by Andy Wilson

FM Voice Transmitter -  This miniature transmitter is easy to construct and it's transmissions can be picked up on any standard FM radio.  It has a range of up to 1/4-mile (Tony van Roon's 400 meters) or more, depending on the line-of-sight, obstructions by large buildings, etc.  It is great for room monitoring, baby listening, nature research, __ Designed by Tony van Roon  VA3AVR

FM Wireless Mike -  Low power frequency modulated transmitter using two transistors.  The circuit works with 9v power supply

Foldback Loudspeaker System for Musicians -  It uses readily available drivers and can be built using basic hand and power tools. __ SiliconChip

Four channel power Amplifier with bi-amping & bridging options -  After building the Micro-Amp, I was not only impressed with the performance of the LM4780, but also felt ready to tackle a more ambitious metalwork project.  This is the result: four channels, with options for bi-amping and bridging. __ Designed by Mark Hennessy

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