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Amplifiers: Audio Circuits
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Last Updated: November 30, 2017 10:27 AM

Circuits Designed by Dave Johnson, P.E. :

Pop Free Microphone On/Off Switch Circuit  -  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 . . . Circuit by David A. Johnson P.E.-February 15, 2002

Remote Range Extender TV/VCR  -  I often get frustrated by how poor some infrared remotes in many new electronic devices operate.  I used to be able to turn on the TV from 30 feet away.  Now, it seems that I have to get within 15 feet.  To address this issue, I designed the circuit shown below.  The circuit taps into the TV remote’s existing infrared LED and drives 8 more efficient devices.  The result is a communications range some 4 to 5 times longer.   . . . Hobby Circuit designed by David Johnson P.E.-December 14, 2009

Remote TV Camera Power  -  A while back I received an email from a company with a problem.  They needed a security camera installed at some remote location.  The camera was a high quality color camera sending out standard NTSC video through a long 500 foot 50 ohm coax cable.  With some difficulty they got the coax strung.  They were told that there would be AC power near the camera location to power that device.  But, they then learned that in fact, there was no power available.  They thought about using a solar panel and a battery but they decided to call me for help instead.  Was there some way to power the camera without stringing another cable? . . . Hobby Circuit designed by David Johnson P.E.-July 03, 2011


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


Natural Radio Reception -  "Natural Radio" is a fancy name for radio noise with natural origins, mainly lightning.  At first, you might think that listening to lightning crackles is pretty uninteresting but as it turns out, electromagnetic radiation from lightning can travel great distances and undergo strange modifications along the way __ Contact: Charles Wenzel of Wenzel Associates, Inc.

NE555 drives a speakes: Pulse Width Modulation Amplifier -  NOTE :  Hand Drawn Circuit.  This idea is used in old days.  Old engineers could not get the good audio transistors.  Therefore , they tried to construct an audio power amplifier with a chap switching transistor.  ***
I tried to use this method with a favorite 555 type IC. __ Designed by Sunamura Kazuhiro

Negative AIR Ioniser with Rotating Ion Thrust Emitters -  A fun way to show that an air ioniser is really working, using a self-propelled spinning emitter. __ Designed by Henry 

Negative feedback Design for Amplifiers -  how to modify a small class AB amplifier for low distortion and minimal power drain __ Designed by Lazar Pancic

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

NICAM Tuner -  I built this back in 1991 when NICAM was an extremely expensive option on AV equipment.  It was used in the same way as a modern "set top box", and features a Scart socket which could be used as an input or output. __ Designed by Mark Hennessy

Nine Volt Battery Eliminator -  for guitar pedals, radios etc __ Designed by G. Forrest Cook

No-CA3080 Guitar Compressor -  The TDA7052A is a readily available amplifier chip (Farnell # 526198) that has a DC controlled volume input.  Here, the IC is used as the variable gain amplifier in a guitar compressor, so the effect can be accomplished without the hard to obtain CA3080 operational transconductance amplifier (OTA).  Note that the suffix-less TDA7052 does not have DC volume controlmust register on this site __ Designed by Published in Elecktor July/Aug, 2010

Noise Canceling Electret Microphones-WB9YBM -  Schematic only __ Designed by va3iul

Notch Filter Autotunes for Audio Applications -  24-Jun-10 EDN-Design Ideas Tracking notch filters find use in harmonic-distortion analyzers; they also can remove heterodyne noise from ham-radio systems.  A conventional tracking switched-capacitor notch filter relies on a bandpass filter, a voltage-to-frequency converter, and a notch filter to track the incoming signal and remove undesired tones.  The bandpass filter in these circuits sometimes adjusts to the wrong frequency, meaning that the undesired tone would have no attenuation __ Circuit Design by John R Ambrose, Mixed Signal Integration, San Jose, CA

Novel buzzer using a relay & transformer -  This novel buzzer circuit uses a relay in series with a small audio transformer and speaker.  When the switch is pressed, the relay will operate via the transformer primary and closed relay contact.  As soon as the relay operates the normally closed contact will open, removing power from the relay, the contacts close and the sequence repeats, all very quickly __ Designed by Tom XxTomxx14 @ ao l. com

OCTAL Phono Preamp -  This preamp design started out as a conventional three stage cascade with feedback RIAA equalization.  I decided on 6SL7's running into 6SN7's.  I figured it would be a good match (electrically and asthetically) for my 2A3 Amp.  After thinking it through I thought I might just try passive RIAA.  (Even a better matchno feedback!!!) I noticed a neat RIAA preamp circuit in the back of the RCA Tube Manual RC-19 that used a single 7025 per channel __ Designed by Bob Danielak

Octave Screamer -  Note that the octave module consists of only five parts – input capacitor, transformer, two germanium diodes, and an output volume pot.  The logical extension of this idea would be to add a DPDT switch so the signal could be routed to either the octave circuit or the TS tone controls.  Each path ends with a volume control and the switch __ Designed by Scott Swartz

Omega -  A versatile FET booster engine. __ Contact: holler @ runoffgroove.Com

On/off buffer switches analog or digital signals -  30-Mar-06 EDN-Design Ideas Use an op amp and a dual SPST to switch signals under digital control __ Circuit Design by Liviu Pascu, Kepco, Flushing, NY

Onboard JFET Preamp -  After the unexpectedly big success of my JFET bass preamp I decided to build an onboard version.  For a Jazz Bass-like instrument, I had to get along with three controls, maybe some switches if I used push-pull pots.  Further, I wanted the functions of the knobs unchanged (volvoltone) and, if possible, use the original pots.   This preamp features independent buffer stages for both pickups, a "Big Muff" style tone control with switchable mid cut and a gain/buffer stage for the output. __ Designed by Albert Kreuzer

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!

One Watt 2.3 GHz RF Amplifier using a MRF2001 -  Simplicity and repeatability are featured in this 1-watt S-band amplifier design.  The design uses an MRF2001 transistor as a common base __ Designed by Michael Micili

One Watt 2.45 GHz Linear Amplifier -  Schematic: Reversed PCB pattern: BOM: Schematic Reference Value Package Capacitors C1 1 µF electrolytic, 10%, 16V SMT or leaded C2, C3 1000 pF ceramic, X7R, 50V 0603 SMT C4 22 pF Johanson ceramic 5%, 100V 0504 SMT C5 3.3  pF __ Designed by www.gbppr.org

One Watt Audio Amp using a TDA7052 -  Ham RadioSchematic __ Designed by Guy Roels ON6MU

One Watt Audio Amplifier Project (Using the TAA300) -  I built this audio amplifier with the TAA 300 Integrated Circuit   (IC) to have on the work bench an independent amplifier to test audio signals coming from radio receivers or audio oscillators.  It is an excellent amplifier to drive an eight ohm loudspeaker.  You can use it, for example, as an audio amplifier for the FM one transistor receiver known as the Radio Shack Special and/or the TDA 7000 FM receiver; also to test the workings of a pulse oscillator or any other kind of audio oscillators. __ Designed by braincambre500 @ yahoo.com

One Watt Class-C Amplifier -  schematic only, no circuit description __ Contact: Charles Wenzel of Wenzel Associates, Inc.

One-capacitor powers audio mixer -  03/14/97 EDN-Design Ideas Micro power and low-voltage op amps allow you to build high-performance analog-signal processors that require no batteries or wall transformers, this simple mixer is powered using one large capacitor such as a Supercap or Dynacap for some Time __ Circuit Design by Aleksandr Belousov, Rego Park, NY

Op-Amp Audio Amplifier -  The above circuit is a versatile audio amplifier employing a low cost LM358 op-amp.  The differential inputs give the amplifier excellent immunity to common-mode signals which are a common cause of amplifier instability.  The dotted ground connection represents the wiring in a typical project illustrating how the ground sensing input can be connected to the ground at the source of the audio instead of at the amplifier where high currents are present. __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Op-Amp Microphone Preamplifier -  A high quality microphone preamplifier using a single power supply, suitable for dynamic or electret microphones.  The op-amp used can be any low noise, high performance type, e.  g.  NE5534, TL071, OPA 371 etc __ Designed by Andy Collison

Optical string-tuning tool -  This tool assists you in tuning your string instrument to a given tone.  It utilizes the stroboscopic effect to give feedback about the adjustment of your instrument.  The two LEDs on the board blink with the frequency that the chosen tone has.  When

Opto Compressor/Limiter Side Chain with Gain Reduction Metering -  Circuit Diagram Only __ Contact: info @ forsselltech . com

Opto Gerbers -  Circuit Diagram Only __ Contact: info @ forsselltech . com

Optp Stereo Link -  Circuit Diagram Only __ Contact: info @ forsselltech . com

Oscillator or Joystick Controlled AM bisonic Pan-Rotate -  A system that rotates mono or B-format soundstage signals by joystick control or spins them continually with an oscillator.  Also creates some attractive lissajous curves as a fortunate by-product. __ Designed by Henry 

OTP µC controls Boomer Amplifier -  03/18/99 EDN-Design Ideas NOTE :  Page includes several designs.  Scroll to find this one.  Figure 1 shows a circuit that uses a one-time-programmable (OTP) µC in an unusual way.  A COP8SGR7 µC uses digital signals to "bit-bang" an LM4835 (dubbed "Boomer" by National) amplifier.  Although the amplifier is designed for potentiometer control, you can modify it to make it a fully digitally controlled part.  Figure 2 shows the flow chart for the control process. __ Circuit Design by Wallace Ly, National Semiconductor Corp, Santa Clara, CA

Output Current Limiter -  (spice design) __ Designed by Rick 

Output Current Limiting -  (spice design) __ Designed by Rick 

Output Stage -  (spice design) __ Designed by Rick 

Output Voltage Limiter -  (spice design) __ Designed by Rick 

Output Voltage Limiting -  (spice design) __ Designed by Rick 

Panner Waveform Generator -  analog synth CV source for the Voltage Controlled Panner __ Designed by G. Forrest Cook

Parabolic Microphone -  Whether you want a Parabolic Dish or a Shot Gun Type of Mic, the electronics is Basically the same.  My Experience with Shotgun Mic's is not that good.  I prefer the Parabolic __ Designed by G.L. Chemelec

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


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


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