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Amplifiers: Audio Circuits
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Audio Amplifiers:   #'s       A - D        E - M        N - R      S - U     
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Last Updated: December 30, 2017 02:09 PM

Circuits Designed by Dave Johnson, P.E. :
Audio Amp + 3Khz Filter  -  This circuit is the audio amp section for a complete optical transmitter.  The circuit amplifies and filters the voice audio signals from an electret microphone.  The circuit is described in more detail in . . . Circuit by David Johnson P.E.-June 04, 2000

Band Drummerís Microphone Switch  -  I received an email from guy who plays drums for a small band.  He wanted a simple way to turn on and off his microphone with just a tap of his drum stick onto a small box.  The circuit below performs this task with the aid of a piezo device as a shock sensor and a small dual coil latching relay with two sets of contacts.  The contacts can be wired any number of ways to a microphone circuit . . . Hobby Circuit designed by David A. Johnson P.E.-October 16, 2011

Boost Infrared TV/VCR Remote Signal  -  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 Dave Johnson P.E.-October 05, 2005

DVD Recorder + TV Camera Make Cheap Data Logger  -  Sometimes recording the results of a test requires as much ingenuity as designing the product.  Consider a situation which requires the collection of many different variables over a long period of time . . . Hobby Circuit designed by David A. Johnson P.E.-April 01, 2005

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

Audio Filter Suppresses Noise andHum -  03/02/06 EDN-Design Ideas Passive filter requires no dc powerThe low-cost composite passive filter in this Design Idea requires no dc power and can enhance the performance of audio equipment and instrumentation by rejecting power-supply hum and spurious pickup from AM, FM, and low-band VHF transmissions   (Figure 1). __ Circuit Design by Richard Kurzrok

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. __ Designed by Richard Torrens

Audio Indicator -  This circuit can be used to remotely monitor a loudspeaker, alarm, or audio source for presence of an audio waveform.  It can also be directly connected across loudspeaker terminals used as a peak indicator. __ Designed by Andy Collison

Audio Level Control Device -  Controlling the level of an audio signal by means of an applied voltage or current has always been problematical but often desirable, particularly when it is necessary to control a circuit from a computer.  This App Note deals with voltage or current controlled attenuators using optocouplers, primarily in relatively static situations   (as opposed to the dynamic control that occurs in compressors, limiters and noise gates __ Designed by Solines, a Cassio Company

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 Light Modulator -  Audio light modulations add to  enjoyment of music during functions organised at home or outdoors.  Presented here is one such simple circuit in which light is modulated using a small fraction of  audio output from  speaker terminals of  audio amplifier.  The output from  speaker terminals of audio amplifier is connected to a transformer

Audio Limiter for NBFM -  This image is of a hard audio limiter used to limit the amount of deviation in an exciter.  After the "knee" the compression ratio is infinite to 1   (hard limiter.)  Smaller amounts of compression ratio can be achieved by inserting resistance between the output of the rectifier, and the DC input of the FET   (gate.)  This circuit can be used ahead of the processing in a standard exciter to add compression, or hard limiting. 
The "R" and "G" are red and green led's.  The op amp can be a 5532, LF-353, or TLO82. __ Designed by Kevin K. Custer  W3KKC

Audio Line Driver -  A stereo line driver for feeding long cables or buffering an audio source. __ 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 mixer (ASCII) -  ASCII drawing __ Designed by John Lundgren

Audio Mixer based JFET 2N3819 -  This is the audio mixer circuit based Junction FET   (JFET) of 2N3819. __ Designed by Aaron Cake

Audio Mixer with Multiple Controls -  When recording sound from several orchestral instruments being played by different musicians using a single microphone, the only way to adjust the sound balance is to change the position of the __ Electronics Projects for You

Audio Notch Filter with Frequencies 100Hz-10kHz -  A variable notch filter with both high and low pass filters. __ Designed by Andy Collison

Audio Panner-Voltage Controlled  -  This circuit is used to convert a mono audio signal into a stereo signal that can be panned between the left and right channel by a 0-10V control signal, it is intended for analog synthesizer systems.  The circuit is mainly here for historical reasons, a higher quality panner may be built with the National Semiconductor LM13700 dual transconductance amplifier set up as a pair of voltage controlled amplifiers. __ Designed by G. Forrest Cook

Audio Phase-Shift Oscillator with Amplitude Stabilization -  Here is a phase-shift audio oscillator with excellent distortion characteristics thanks to "softened" diode limiting provided by the 1N914 and resistor divider and degenerated gain provided by the 68 ohm emitter resistor.  For minimum distortion. __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Audio Power Amplifiers -  with: TDA2005, TDA1013B, LM386, TDA2040 and TDA2003. __ hobbyteam @ hobby-hour.com

Audio Preamplifier -  A 2 stage audio pre-amplifier with very good performance.  This preamplifier has two direct-coupled common emitter stages and uses series-voltage feedback.  The circuit has high input impedance, low output impedance, voltage gain can be set independently and has low noise levels and good signal noise ratio. __ Designed by Andy Collison

Audio Pre-Amplifier -  Circuit Only __ Designed by Tony van Roon  VA3AVR

Audio Refinement Complete integrated Amplifier -  The Complete' is made to Design by Yves-Bernard Andre   (YBA).  My unit s/n is an early 00026, probably later copies are different from the first batch.  I used the amp for two years, and the only reason to dig inside it, apart from 'how they did it' curiosity, was to disconnect the volume pot motor.  It returns to zero at each power down __ Contact: klausmobile @ yahoo.Com

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 Spectrum Analyzer & Equalizer Designs -  A spectrum analyzer can be a powerful tool for keeping your studio well tuned.  Besides its obvious usesfor adjusting octave or one-third octave room equalizersa spectrum analyzer can also be used to check the response of a tape recorder, or even help identify the rumble frequencies in an air conditioner.  Unfortunately for many studios, the high price of a commercial spectrum analyzer presents a major problem __ Designed by Ethan Winer

Audio spectrum analyzer on PIC32 -  This simple audio spectrum analyzer is based on PIC32 proto board on PIC32MX360F512L with 320◊240px colour LCD   (LVC75Z779 Eval Board).  The analyzer can be connected to unamplified audio source like PCís sound card, MP3 player and so

Audio Spectrum Monitor -  A digital audio signal processing experiment of real-time FFT   (Fast Fourier Transform) analysis. __ Designed by The Electronic Lives Manufacturing-presented Chan

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 Visual Indicator for Telephones -  Many a times one needs an extra telephone ringer in an ad joining room to know if re is an incoming call.  For example, if  telephone is installed in  drawing room you may need an extra ringer in  bedroom.  All that needs to be done is to connect  given circuit in parallel with  existing telephone lines using twin flexible wires.  This circuit does not require any external power source

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 Volume Relay Attenuator with IR Control -  The circuit provides both audio volume and input channel selection.  A stepwise volume control is implemented with a set of small relays and resistors.  In a high-end audio system, a noticable sound improvement over potentiomeneters can be obtained, also over 'audio grade'

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

Audison LR604XR Amplifier (Car Audio) -  Of the few car amplifiers I tested, gutted, decyphered and fixed, this one seems to be the best in design quality.  Too many car amps   (although solidly built) are apparently designed by computer class students, too many traces, too many vias, absolutely wrong component placement etc.  And on schematic level __ Contact: klausmobile @ yahoo.Com

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

Automatic Mike Muter for Singing Guitarists -  The average musical Do-It-Yourselfer starts building guitar effects by making a distortion pedal of some sort.  It's a good introduction to musical electronics, and pretty simple as well, since getting a circuit NOT to be linear has never been hard.  But there comes a time when you have to stop thrashing the strings in your bedroom, get up on stage and *play*.  When you get to there, you run into all kinds of little problems that you never encountered back in your room. __ Designed by R.G. Keen

Automation Comes to the Harmonica -  11-Mar-11 -Design News:   Advanced Automation has been edging into our working lives for decades.  While most of the inroads made by automation have been in manufacturing, these technologies are being increasingly applied in entertainment.  Jon Sorkin has created a gadget that plays programmed songs with a harmonica.  The __   Gadget Freak-Case #182

Awfully Antique Audio Amplifier  -  A funny retro project, and a new standard for schematic symbols! __ Designed by Manfred Mornhinweg

Azabache -  An original overdrive inspired by classic Fender amps. __ Contact: holler @ runoffgroove.Com

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Audio Amplifiers:   #'s       A - D        E - M        N - R      S - U        V _ Z

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