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Amplifiers: Audio Circuits
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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 Drummer’s 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:

Digimodes improvement for the TS-450/690 -  Fix that nasty distortion on the packet connector audio output! __ Designed by Manfred Mornhinweg

Digital Delay Unit for Surround Sound -  The Mitsubishi M65830 Delay IC has been discontinued (for reasons beyond my comprehension) , and so far a suitable replacement device has not been found.  This means (of course) that you will be unable to build this delay circuit.  I have left the project in place as reference, and the overall connection schematic is still valid if (when?) a replacement for the M65830 is located.  The project will be updated at that time.  In the meantime, just ignore the delay circuit __ Designed by Rod Elliott  ESP

Digital Voice Recorder ISD2560 -  This project is based on ISD2560P IC which allows us to record 60 seconds voice and playback it with very high quality.  As shown in the schematic, we input the voice by using an electret microphone.  If a dynamic microphone is used, R2, R3, R4

Digital volume control -  The Tiny Audio Amplifier kit is a good choice for battery operation.  It is based on LM386 IC.

Digital Volume Control -  This circuit could be used for replacing your manual volume control in a stereo amplifier.  In this circuit, push-to-on switch S1 controls the forward (volume increase) operation of both channels while a similar switch S2 controls __ Contact: IQ Technologies

Direct Injection Box for Musicians -  Don't put up with hum.  This versatile DI box converts an unbalanced input to a balanced output signal and includes a 3-band equaliser. __ SiliconChip

Direct Injection Box for Recording & Psystems -  An essential companion for the mixer for stage or recording work __ Designed by Rod Elliott  ESP

Directional Microphone -  With the possible exception of sophisticated shotgun microphones or microphone arrays, effective directional microphones usually employ parabolic reflectors or horns.  Parabolic reflectors about the size of a modern satellite receiver antenna, perhaps 2 feet across, perform quite well but are a bit obtrusive.  These are commonly seen on the sidelines at football games.  But it turns out that simple horns or cones work very well as directional sound collectors, are easier to handle, and don't look like microphones.  They do look a bit like megaphones, witches' hats, or traffic cones, all of which might make great microphones! In fact, a pair of cheerleader megaphones might make a great two-way communications system __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Discrete JFET Bass Preamp -  I wanted a warm, tube-like sound with as few stages as possible.  I believe that part of the clarity and directness of a tube amp comes from the fact that there are so few phase invertions compared to a normal solid state (not to mention the different kinds of unpleasant distortions made by op-amps).  So I came up with the absolute minimum setup: Two (inverting) gain stages and one source follower/impedance converter.  JFETs, because they behave similar to tubes at overload conditions (of course, nothing but a tube really sounds like a tube...)   The EQ Section was originally planned to be like an Ampeg SVT filter.  It sounded good, but I could not get rid of the hum (used a small transformer for the filter coil), also it was rather noisy compared to the rest of the preamp.  So I had to make a compromise (op-amps!), but this circuit really works fine, and most important, it can be bypassed.  In fact I rarely need it, just use the "Ultra High"- and "Ultra-Low"-switches. __ Designed by Albert Kreuzer

Distance Sensing-devices for wireless distance & position Determination -  Since the early seventies we did build sonar devices to control our self made analog electronic music synthesizers.  In those years, simple to use transducers were not readily available on the electronic component market and so, we had to make our own, based on designs used for underwater hydrophones.  (Quarz crystals, inductive devices, self made condensor microphones etc...).  Although the focus of our research later on became doppler based sonar and radar movement detection and gesture analysis __ Designed by Dr.Godfried-Willem Raes

Distortion effects using an LM386 Audio Amplifier IC -  A few months ago, Aron Nelson released the Smash Drive.  The circuit ingeniously used an LM386 audio power amp chip to produce great distortion sounds.  Aron based his work on that of Tim Escobedo.  Tim's Stupidity Box was another great sounding unit and beautifully simplistic.  The Smokey Amp by Bruce Zinky was another design that used a 386 for some great sounds. __ Contact: holler @ runoffgroove.Com

DIY 50W Amplifier based on ICL8063 -  This is a handy, easy to build general purpose 50 watt amp.  The amp has an input for a radio, TV, stereo or other line level device.  It also has a phono input for a record player, guitar, microphone. __ Designed by Aaron Cake

DIY Bias Probe -  DIY Bias Probe __ Designed by Guitar Effect RC Keen

DIY Serial MIDI Interface 80C51/80C31 Version -  Run out of ISA card slots in your PC? Want a real MIDI interface instead of the toy interface that is built-into your sound card? Got a COM port handy? Then build the Serial MIDI Interface.  This page describes how to build this full-bandwidth single-port (one input and one output) MIDI interface.  The interface is buffered (that is, if the PC gets behind you won't lose data) and it works in Windows 3.1 and Windows 95 using a special (and very well-behaved) device driver.  A simpler version, using an Atmel AT89C2051 microprocessor, __ Designed by Paul Messick

Dog Repellent Project -  The electronic dog repellent circuit diagram below is a high output ultrasonic transmitter which is primarily intended to act as a dog and cat repeller, which can be used individuals to act as a deterrent against some animals.  It should NOT be relied upon as a defence against aggressive dogs but it may help distract them or __ Designed by Popescu Marian

Door Phone Intercom -  A simple 2 way Intercom based on the LM386386 using 8 ohm speakers __ Designed by Laurier Gendron & Andy Collison

Double D -  Two channels of buxom distortion. __ Contact: holler @ runoffgroove.Com

DPA 220 Amplifier schematic -  T1 to T6 create the input differential stage.  The D7 and D8 zener diodes stabilize at 5V.  These are just the simplest low-power zeners, only they have to be coupled in tolerance of 200 milivolts, which should not be a problem.  T1 to T6 are common all-purpose low-power transistors with high Hfe.  These six and maybe the next four have to be coupled in tolerance of 25%. __ Designed by Rysanek Frantisek

DPA 330 : 170 W in 4 ohms-FET's. -  Now we're getting to the best stuff.  Let's discuss some parts: As you can see, the input stage is quite similar to the previous typesit was originally developed for this one.  There's only one new thingthe servo feedback amp OA1.  It subdues the DC voltage on the output below 1 mV.  The real news come in the power stage.  The fets are completely different than bipolars.  A problem is how to eliminate the gap causing crossover distortion. __ Designed by Rysanek Frantisek

DPA 440 Amplifier schematic -  Audio power amplifier circuit diagrams / circuit schematics __ Designed by Rysanek Frantisek

DPA 880 : 400 W in 4 ohms-bipolar -  Again, this one is similar to the above ones, only it uses serial connection in the power stage to allow a higher voltage:  The bias current is 110 mA; The output coil is 14 turns of 1.8mm wire on an 11mm diameter;
The trafo should be about 2*57 Volts and 20 to 25 amps !!! __ Designed by Rysanek Frantisek

Dracula MOSFET Power Amplifier -  Simple Class-A power amp that uses complementary pair of IRFP240 and IRFP9240 MOSFET transistors.  The intention of this project was to build simple, but high quality amplifier.  The aim was reached by integrating the whole input driver in one IC and adding high power transistor output stage.  As you can see on the schematic the amplifier has very simple structure.  At the input there is high quality and relative high power TI IC OPA552.  It drives a complementary pair od MOSFET transistors IRFP240 and IRFP9240.  The gain of the whole circut is set to 40x.  The TL431 is to set the operation point of output transistors.  The idle current is set to 80mA, so the amplifier works in A class for it's first few watts.  The more current the longer it stays in A class, but the more power to be dissipated.  With 80mA and these heatsinks it still goes very hot after long playing.  

Drum percussion sensor Schematics -  The signals produced by most percussion sensors will require some processing before they're useful as triggers.  Usually this means converting an oscillatory signal into a single unambiguous pulse that is appropriately scaled to carry the widest possible range of velocity information to the circuit being controlled.  The circuitry in the diagram below performs this function. __ Designed by John Simonton

Drum Tone Oscillators -  The circuit shown is the most interesting of several drum oscillators on an analog sound board that appeared as part of an article in the June 1993 issue of Electronics Now.   Like most drum tone oscillators, the circuit is a very high Q resonant filter that is only slightly overdamped and on the verge of oscillating.  Triggering pulses (coupled through C5 and R5 in the circuit above) provide an excitation signal that "rings" the oscillatoran analog of the rapidly decaying envelope of percussion sounds __ Designed by John Simonton

DS1669 Digital Potentiometer -  The DS1669 Dallastat™ is a single digital rheostat or potentiometer with access to all three potentiometer terminals.  The potentiometer has 64 wiper positions with equal or linear resistive step sizes.  This device has both positive and negative 8V (max) supply inputs for maximum wiper outputs __ Maxim Integrated

DSP Musicolour Light Show; Pt.2 -  In last month's first part, we described the circuit operation of the DSP Musicolour.  In this instalment, we guide you through the construction.  The operation of the firmware and troubleshooting tips will be described next month.  In this issue there are also notes and errata for the schematic published last month. __ SiliconChip

DSP Musicolour Light Show; Pt.3 -  In last month's article, we detailed the construction of the DSP Musicolour.  In this month's article, we guide you through the final testing of the DSP Musicolour and give troubleshooting tips.  We also explain the operation of the firmware in more detail as well as discussing possible accessories. __ SiliconChip

DSP Musicolour Pt.1 -  This DSP Musicolour accepts audio input signals and drives coloured lights "in tune" with the music.  Its four output channels respond to different audio frequency bands and the brightness of the lights is in direct proportion to the amplitude of the frequency components.  A dot-matrix LED menu display is featured on the front panel and this also functions as a spectrum analyser or VU meter. __ SiliconChip

DSP Musicolour Pt.4 -  With a small and low-cost add-on PC board, the DSP Musicolour can be operated via an infrared remote controlvery handy if you want to use it in hard-to-reach places. __ SiliconChip

Dual Amp PCB -  containing schematic and gerber files.  For Use with Opto Compressor Project __ Contact: info @ forsselltech . com

Dual Analogue Frequency Shifter -  An audio effects frequency shifter similar to the famous Bode/Moog design from the 1970s. __ Designed by Henry 

Dual JFET-992/993 PCB -  containing schematic and gerber files.  For Use with Opto Compressor Project __ Contact: info @ forsselltech . com

Dual Microphones Separate Voice From Noise -  06/23/94 EDN-Design Ideas The circuit in Fig 1 uses a pair of microphones to extract a voice from a noisy background.  You must mount electret microphones X1 and X2 on the left and right sIdeas of the user's chest.  Sound sources not equidistant from the microphones experience a phase shift.  Because sound travels at 1120 ft/sec, the maximum phase shift for this design's/ __ Circuit Design by Samuel Kerem, Infrared Fiber Systems, Silver Spring, MD

Dual parallel buffered effect loops with blend control. Schematic & perfboard/PCB layouts -  The Splitter-Blend provides two buffered parallel effects loops with a Blend control.  Also, a phase polarity switch is included to allow phase matching of the effect loops.  Possible uses are blending two sets of effects placed in the loops, a signal splitter, a simple mixer, or to blend an effect with the dry signal.  The phase inverter can be used for interesting results when mixing dry and effected signal. __ Contact: holler @ runoffgroove.Com

Dual Phantom Power Pre-Amp -  Schematic only, no circuit description __ Designed by John Simonton

Dual Transformerless Class a Discrete Mike Preamp -  Uses JMP-1 Modules __ Contact: info @ forsselltech . com

Dual Voltage Controlled Oscillator w/Modulator -  Schematic only, no circuit description __ Designed by John Simonton

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, 2005

Dynamic Microphone Amplifier -  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

Dynamic Microphone Preamplifier -  A low noise pre-amplifier suitable for amplifying dynamic microphones with 200 to 600 ohm output impedance. __ Designed by Andy Collison

Dynamic microphone to electret microphone input -  Circuit which works as an preamplifier which allows you to replace an electret microphone with a dynamic microphone. __ Designed by Tomi Engdahl

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