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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: November 30, 2017 10:27 AM

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:


Class A2 SE SV572-160 Stereo Amp -  This amp uses a 6BM8 drive stage similar to the big 833A amp below, except it utilizes CATHODE drive.  I presently have this amplifier set up so i can adjust the grid bias from about +2V to +30V.  There is also a switch that connects the output tube grids to ground (0 Bias) instead of the grid bias supply.  This way i can experiment with various output tubes, including 811A, 812A, SV572-10, SV572-30, SV811-10, etc.  So far, i think the SV572-160 sounds best in this amp.  I think it is because of the cathode drive (also called grounded grid) topology.  I think i like the medium mu transmiting tubes, like 812A, 826, SV572-30 in grid drive amplifiers better.  But in this amp, the 572-160 can be "dialed in" to a nice sweet-spot that sounds great! __ Designed by Bob Danielak

Class A2 SE826 power supply -  The schematic for the power supply __ Designed by Bob Danielak

Class AB inverting Amp uses two floating Amplifier cells -  03/19/09  EDN-Design Ideas Transistors often find use as three-pin amplifier devices, in which the input and the output share one pin.  Thus, the input and the output must have the same voltage at this pin.  On the other hand, a four-pin amplifier could isolate the circuit's input and output.  Using optoisolators, you can design a four-pin Class AB amplifier.  Although the output voltage of an optoisolator curtails its usefulness, you can add discrete transistors to form an isolated amplifier. __ Circuit Design by Joseph Wee Ting, Institute of Atomic and Molecular Sciences, Sinica Academy, Taipei, Taiwan

Class B Amplifier Has Automatic Bias -  22-Oct-09 EDN-Design Ideas Biased transistors minimize distortion __ Circuit Design by Pierre Corbeil, Paradox Innovation, Montreal, PQ, Canada

Class-A Audio Amplifiers -  A class-A audio amplifier is pretty wasteful of power but when plenty of power is available the simplicity is attractive.  Here is a simple darlington transistor example intended for use with a 5 volt power supply __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Class-A MOSFET Amplifier -  I am using this Class A Amplifier with a 12AU7 based valve preamp.  It produces the most purest sound.  I have no idea of distortion levels etc.  but it has a very fine grain and delicately textured quality.  With only one watt of output efficient speakers must be used.  Bass is better than the design predicts and the amp drives my 12" 63L based 3-way speakers with ease.  

Classroom Microphone SystE - M -  This audio amplifier circuit is useful in classrooms to reduce the strain of lecturing , if the surrounding environment is noisy.  It uses the power amplifier IC LM380 that gives 2 watts output which is sufficient in a confined area.  The amplifier is portable and the whole circuit and the battery can be enclosed in the Speaker __ Designed by D Mohankumar

Closer look at the FET booster based on a vintage Fender 12AX7 input stage. -  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

CMOS IC 1 kHz Audio Oscillator -  This circuit consists of a CMOS square wave oscillator on a frequency of approximately 1 kHz.  The RC filter, which has a roll-off frequency of 500 Hz, filters the harmonics, providing a sine-wave output.  The oscillator has many uses; sidetone circuits in transmitters and signal injectors for audio tests are just two __ Designed by Peter Parker VK3YE

CMOS Inverter VCO tunes octave to UHF -  11/19/98 EDN-Design Ideas NOTE :  File contain several designs.  Scroll to find this one.  A robust and versatile vco provIdeas a stable output to 300 MHz (Figure 1).  The circuit's simplicity, unconditional stability, and consistent high-drive capability over an octave make the oscillator ideal for many applications, such as synthesized sources, local oscillators, and transmitters.  The AHC logic family (Texas Instruments, www.ti.com) makes the circuit's performance possible.  AHC is a relatively new line of CMOS logic whose high speeds and good noise performance allow oscillator operation into regions in which bipolar-junction-transistor and FET designs prevail. __ Circuit Design by Shawn Stafford, AM Communications Inc, Quakertown, PA  

CMoy pocket headphone Amplifier -  Chu Moy designed a very popular headphone amplifier that’s easy to build, and it can be built small enough to fit in a pocket, power supply and all.  It’s powerful enough to drive very inefficient headphones to thunderous volumes from even weak sources, and it sounds excellent considering that you can build a bare-bones CMoy amp for just US$20, and a pretty nice amp for under $50.  Considering that the cheapest of the worthy commercial amps is $100 and most of them are in the $200+ range, this is a very worthwhile cost difference. __ Designed by contactme2016 @ tangentsoft . com

Collection of Audio Amplifiers -  Collection of audio amp circuits. __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Colour Organ -  Three Lamp-Channels OutputBuilt-in Electret Microphone __ Contact: Flavio Dellepiane, fladello @ tin.it

Colour Organ based on a PIC16F84 microcontroller including Schematics & source code -  PIC Project  This unit uses a PIC16F84 with an 8 bit A/D.    The signal from both stereo channels is combined and digitized.    Each of 5 frequency bands is processed using a 16 point FFT.    Then the level of each channel is output as PWM (pulse width modulation) to a set of solid state relays __ Designed by Luhan MonatMesa Arizona

Combine Power Supply & Audio Amplifier -  12/20/01  EDN-Design Ideas The circuit in Figure 1 can help if you must transfer dc power and audio over a pair of copper wires.  One application for such a circuit is a low-cost door-opening system with speech input.  The circuit uses only one IC, the well-kn __ Circuit Design by Susanne Nell, Breitenfurt, Austria

Compact 3W BTL Audio Power Amplifier TDA7056 -  Bridge-tied-load (BTL) configuration in an amplifier is basically a H-network  with the loud-speaker as the “bridge” between two active valve or switcher.  This configuration allow a full alternating current signal to be produced at the load (loudspeaker) without a transformer or a symmetric power supply.  

Compact DJ station -  Two Phono/Line switchable inputs; Powered by 9V Battery or external supply Adaptor __ Contact: Flavio Dellepiane, fladello @ tin.it

Compressor/Limiter/Clipper for FM Broadcasting -  Audio signals as music or speech have big dynamic ranges.  There are silent and loud sections.  These audio signals aren't too good for a transmitter, which requires audio signal with constant level on the input.  Limiter is a device, __   Jan Kolar

Computer Audio Booster -  Here is a simple amplifier for boosting the audio level from low-power sound cards or other audio sources driving small speakers like toys or small transistor radios.  The circuit will deliver about 2 watts __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Computer Microphone -  This circuit was submitted by Lazar Pancic from Yugoslavia.  The sound card for a PC generally has a microphone input, speaker output and sometimes line inputs and outputs.  The mic input is designed for dynamic microphones only in impedance range of 200 to 600 ohms.  Lazar has adapted the sound card to use a common electret microphone using this circuit __ Designed by Andy Collison

Condenser Mic Audio Amplifier -  The compact, low-cost condenser mic audio amplifier described here provides good-quality audio of 0.5 watts at 4.5 volts.  It can be used as part of intercoms, walkie-talkies, low-power transmitters, and packet radio receivers.  Transistors T1 and T2 form the mic preamplifier. __ Designed by D. Prabakaran -  c Electronics For You Mag

Condenser Microphone Uses Dc-Coupled Impedance Converter -  03/15/12  EDN-Design Ideas Eliminate transformers and coupling capacitors in this self-balancing microphone interface.  The diaphragm of a condenser microphone is the movable plate of a capacitor.  With a polarized capacitor, the vibration of the diaphragm in relation to the back plate produces an ac audio-output voltage.  The condenser capsule has a capacitance of 10 to 60 pF; thus, you should connect it to an impedance converter with extremely high input impedance for a flat frequency response. __ Circuit Design by Dimitri Danyuk, Miami, FL

Condor CAB Sim -  A professional-quality 4x10 open-back speaker cabinet simulator. __ Contact: holler @ runoffgroove.Com

Constant Q Expandable Graphic Equaliser -  Constant Q design.  Can be made using as many or as few sections as needed __ Designed by Rod Elliott  ESP

Convertible Single Ended SV572-30/3 Stereo Amp -  This project makes use of at least two of the new SV572 series audio power triodes from Svetlana.  This series includes the SV572-3 , SV572-10 , SV572-30 , and SV572-160.  The circuit topology is easily re-configurable ("convertible") to use either the -30 (in Class A2Zero Bias operation) or -3 (in Class A1 operation).  In addition, the -30 can be configured for two different drive schemes (standard grid driven configuration or Cathode Driven.  A set of switches are used to reconfigure (with power off).  But for clarity, the schematics are re-drawn for each mode as shown below __ Designed by Bob Danielak

Converting the Stereo Audio Distribution Buffer Into Stereo Audio Distribution Amplifier -  The stereo audio distribution buffer published on page 94 of July 2013 Edition of EFY can be converted easily into stereo audio distribution amplifier.That will add gain and will give new __ Electronics Projects for You

CPLD automatically powers itself off -  04/13/06  EDN-Design Ideas Add a few discrete components to a CPLD to implement a battery-powered system's power-down circuit __ Circuit Design by Rafael Camarota, Altera Corp, San Jose, CA

CPLD autonomously powers battery-powered systE - M -  12-Apr-07 EDN-Design Ideas CPLD controls power-on and off of intermittent-battery-powered system __ Circuit Design by Rafael Camarota, Altera Corp, San Jose, CA

Crest Audio LT Series LT100 LT1500 & LT2000 SchematIC Set -  A commercial Class D Amplifier, complete schematics in PDF format

Crystal Radio (and other purpose) Audio Amplifier -  Here is a simple audio amplifier using a TL431 shunt regulator.  The amplifier will provide room-filling volume from an ordinary crystal radio outfitted with a long-wire antenna and good ground.  The circuitry of such a radio is similar in complexity to a simple one-transistor radio but the performance is superior (with the exception of the amazing one-transistor reflex).  The TL431 is available in a TO-92 package and it looks like an ordinary transistor so your hobbyist friends will be impressed by the volume you are getting with only one transistor and the amplifier may be used for other projects, too.  Higher impedance headphones and speakers may also be used. __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Cuckoo-song Generator -  This circuit generates a two-tone effect very much alike the cuckoo song.  It can be used for door-bells or other purposes thanks to a built-in audio amplifier and loudspeaker
Used as a sound effect generator it can be connected to external amplifiers, tape recorders etc.  In this case, the built-in audio amplifier and loudspeaker may be omitted and the output taken across C8 and ground. __ Contact: Flavio Dellepiane, fladello @ tin.it

Curiously Low Noise Amplifier -  The Curiously Low Noise Amplifier takes advantage of the wonderful noise characteristics of the 2SK117 JFET that boasts a noise voltage below 1 nV/root-Hz and virtually no noise current.  The noise voltage of the amplifier is only 1.4 nV/root-Hz at 1 kHz, increasing to only 2.7 nV/root-Hz at 10 Hz.  The noise current is difficult to measure, so this simple utility amplifier can see the noise from a 50 ohm resistor and a 100k resistor, too.  (The 1.4 nV input-referred noise will increase to about 1.7 nV with a 50 ohm resistor, instead of a short, and a 100k resistor will give an input-referred noise near 40 nV, with very little contribution from the amplifier.) __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Current Feedback Amp -  The amplifier shown here was previously incorrectly referred to as 'El-Cheapo'.  Thanks to a reader who had a copy of the original 1964 article, it was immediately obvious that my recollection was flawed in the extreme. __ Designed by Rod Elliott  ESP

CW filters -  Two projects are described here, both of which may be used to enhance simple receivers of the types already described.  These two circuits may be built on the same circuit board and the OP-AMP IC, (LM324), has sufficient capacity to accomodate both circuits. __ Designed by Harry Lythall-SM0VPO

Daisy MP3 player project -  The Daisy is a multipurpose sound player for embedded applications.  It can be used as a standalone personal music player,as the sound for an art project, in a kiosk, as a museum tour guide, in a toy, or anywhere that high quality embedded audio is desired.

Darling & DC Darling SE 1626 Amps -  This has become a very popular set of amp designs.  They are all based upon the 1626 Triode output tube and the philosophy to keep things SIMPLE.  I am continually amazed how good these amps sound for what they are.  The name "Darling" came from a good friend's description of my original design.  It looked like a miniature version of "full-sized" SE 300B.  The name stuck  Click  HERE  to find out more __ Designed by Bob Danielak

DC Coupled Phono Preamp -  Schematic, Only     Using 6SL7 instead, and DC-coupling of the two stages.  RIAA Preamp based upon the classic RCA 12AX7 design. __ Designed by Bob Danielak

DC Fault Protection for Audio Amplifiers -  Circuit ideas how to replace traditional CD protection relays with MOSFETs __ Designed by R.G. Keen

Dead-Simple Circuit Masthead Amplifier -  Decided to take the plunge and get into digital TV? For most people, it's simplejust plug the new TV or set-top-box into your existing antenna.  But for many, the old TV antenna and cable just won't be up to it.  Here?s a new kit from Oatley Electronics which could solve your digital woes__ SiliconChip

Death of Zen DoZa New Class a Power Amp -  An ultra simple, high performance Class-A power amp.  Revision-A boards now shipping __ Designed by Rod Elliott  ESP

Defeating SCMS on DAY recorders using a Sony CXD2601 chip -  For this modification you have to things to your DAT recorder that surely void your warranty, and can possibly ruin it.  Use at your own risk!  By the way, this circuit could be illegal in your country.  Please consider it "for educational purposes only" :-).  I modified a Sony DTC790 DAT recorder using a circuit designed for recorders with a CXD2601 chip. __ Designed by F.J. Kraan

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

Diff Amp with Current Mirror -  In an audio input differential stage, you often see the simple collector resistor replaced with a current mirror.  Why bother? The payoff is two fold.  First, you get twice the gain and current output, typically a good thing for an audio amp.  And second (spice design) 

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


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