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A 50mW Class-A Headphone Amplifier - The gain of this voltage-feedback design can be set by changing the values of two resistors. The authors presents versions optimized for low and high impedance headphones as well as one that performs well with a wide range of loads.  Designed by Rohit Balkishan  (circuit design added 04/05/06)

A Collection of Amp Applications - AN-106 Analog Devices Application Notes  (app note added 2/06) Examines Some of  Numerous and Widely Used Applications of  Operational Amplifier

A Current-Domain Electrostatic Amplifier for Stax Omega II Headphones - The amplifier operates primarily in the current domain. The first stage is a voltage controlled current sink. The second stage is a current-controlled voltage source. The fourth stage is a constant current sink. The main advantage of current domain amplifiers is speed..... designed by Kevin Gilmore (circuit design added 04/05/06)

A DC-Coupled Tube Amplifier With Futterman Output Stage for Dynamic Headphones - The Futterman output stage in this tube amp offers the choice of DC- and AC-coupled outputs. The class AB design can output up to 24mW into a 30-Ohm load or nearly 500mW into a 600-Ohm load.  Designed by Rudy van Stratum  (circuit design added 04/05/06)

A Digitally Programmable Gain & Attenuation Amplifier Design - AN-137 Analog Devices Application Notes  (app note added 2/06)

A Fender-Tone Tube Headphone Amplifier - This tube amplifier with sonic controls has a paralleled White cathode follower output stage for driving low impedance headphones. The sonic controls consist of a Fender tone stack (bass, mid and treble), and ambience and blend controls. Includes simulation files for use with OrCAD Lite software.  Designed by Alex Cavalli  (circuit design added 04/05/06)

A Gainclone for the PC Age - Audio input comes from either the Line-Out of the PC or an external sound card (described later). A small filter consisting of 680Ω/47pF excludes any RF signals from entering the case. 470nF input capacitor should have a high voltage rating since it protects against line voltages being connected to the amplifier, since it is in the signal path it should be a high quality type....(circuit added 07/08/09)  designed by Malcolm Rix

A Good IR Detector - Some of the companies put two transmitters, one on each side of the detector, to get a good field of coverage for the front of the 'bot and to detect left and right. 'Robots, Inspiration to Implementation has a great schematic that you can use to build one of these. I used all Radio Shack parts for the one I made and it cost about $10 to build. This detector will NOT detect black flower pots nor the bottom of boots (grin)....(electronic Circuit added 03/06)

A HiFi Preamp - The PGA2310 is a pretty neat chip. It's capable of attenuating a stereo source over a 127dB range (-95.5dB to +31.5dB) with 0.5dB steps. It has a maximum gain error of +/-0.05dB, and THD of 0.0004% at 1KHz. The sweet spot between THD and noise appears to be between 3V RMS and about 8V RMS...(circuit added 04/05/06)

A JFET-MOSFET Headphone Driver - This amplifier is based on the MOSFET headphone driver by Greg Szekeres. It has a JFET impedance buffer front-end and a choke-input power supply. The sound characteristic of the amplifier can be tuned by adjusting the low pass filter formed with the input capacitance of the MOSFET.  Designed by Richard Murdey  (circuit design added 04/05/06)

A Low-Voltage Class-A Tube Headphone Amplifier - This OTL design features a high-voltage power supply that is less than half of the one used in the author's first amp and most other tube amps, but without compromising performance.  Designed by Helmut Ahammer  (circuit design added 04/05/06)

A Musical Distortion Primer - This is an introduction to the basic means of distorting a signal in a musically useful way. The approach is as non-technical as possible.  I use the simplest signal waveform, a sine wave, to illustrate all these, although a guitar is much more like a sawtooth than a sine wave. The clipped waveforms will be shown in their raw state....(circuit design added 04/05/06)

A Non-Complementary Audio Noise Reduction System - National Semiconductor Application Note   (app note added 2/06)

A Pocket Headphone Amplifier - This is a Chu Moy headphone amp I made. I got the PCB design from Guzzler from Head-Fi and the original design is very popular and is here. I changed Guzzler's layout so I could use a Taiwan Alpha pot on the PCB. These pots a high quality (some say better than ALPS blue velvet) and are available from Jaycar. You can see the thread here. I also made a DIY Brown dog adapter so I could use two OPA627 single opamps in a dual opamp socket.

A Pure Class A Dynamic Headphone Amplifier - A high-current output amplifier for low-impedance dynamic headphones such as the Grados. The amplifier features an new servo biasing circuit which operates entirely outside the audio feedback loop. The author includes a balanced-bridge version of the amp for headphones that are wired in dual-mono as well as instructions for converting a Grado SR80 to dual-mono operation.... Designed by Kevin Gilmore  (circuit design added 04/05/06)

A Simple Capacitance Multiplier Power Supply For Class-A Amplifiers - A basic circuit is provided in the article, but it is assumed that the builder knows all the pitfalls. The supplied schematic is in fact for a capacitance multiplier filter (not a regulator), but is somewhat lacking (I feel) and can be improved dramatically....(added 04/05/06)

A Single-Ended OTL Amplifier for Dynamic Headphones - A simple OTL design that uses just two tubes (dual triodes) for stereo. It has a common cathode input stage direct-coupled to a cathode follower output stage.  Designed by Aren van Waarde  (circuit design added 04/05/06)

A SRPP-Input Tube Amplifier For Headphones & Loudspeakers - This transformer-coupled design uses a series regulated push-pull input stage and a parallel-triode cathode bias output stage. The audio output transformer is hand-wound from a kit. The amp will drive both headphones and speakers.  Designed by Tony Frazer  (circuit design added 04/05/06)

A Tube Headphone Amplifier/Preamp with Relay-Based Input & Power Switching - A tube headphone amplifier inspired by the "Top-Level" and "No-Compromise" amps of Andrea Ciuffoli, except that the output stage uses a triode-connected pentode. Because this amp also serves as a preamp, the author has put in a sophisticated relay-based switching system (both input source selection and power supply). The power supplies also feature slow-on and stepped delayed turn-on. The power-on LED doubles as a warm-up status indicator.  Designed by Helmut Ahammer  (circuit design added 04/05/06)

A Weighting Filter for Audio Measurements - For noise measurements. Ideal for use with the AC Millivoltmeter above  (electronic circuit added 4/05)

A Zero-Feedback SRPP-Input Headphone Amplifier - Features a series regulated push-pull input stage and transformer-coupled output stage with an output impedance of about 2.5 ohms. It has zero global feedback for open, natural sound without any harshness.  Designed by Simon Busbridge  (circuit design added 04/05/06)

A/V Sender - This circuit provides you with wireless audio and visual transmission to a TV. The TV acts as a receiver, eliminating the need to buy a separate monitor. You can also hook it up to a VCR or CCD Camera, and even set up a remote CCTV security system!....Circuit design (added 02/05)

A4 Power Amplifier - Circuits are shown beginning on page 2.  As the stunningly original (!) name suggests, the A4 contains 4 separate power amplifiers. This unit offers great flexibility, …(schematic added 04/05/06)

AB-3: Digital Nulling of Precision Op Amps - AB-3 Analog Devices App Notes  (app note added 2/06)

Active Bass & Treble Controller - Amplifiers would be nothing without tone controls. They allow us to boost or cut the low and high ends of the audio spectrum. Nobody would buy an amplifier or preamp that did not have them. Because these controls are so important designers spend a lot of time and effort on these circuits.....(circuit design added 09/08)

Active filter circuit & oscilloscope inspect a Class D Amplifier's output - 12/01/06 EDN-Design Ideas: Ease debugging of bridge-output pulse-width-modulated audio amplifiers with this circuit.....(design idea added 12/06

Active Load in Gain Stage - Instead of a resistor at the transistor's collector, you might have seen a current source (active component) substituted in an audio amp's gain stage. Why go through the trouble of the added components? You'll find the active loading of a current source packs ...(spice design added 02/09)

Active Subwoofer & Controller - (electronic circuit added 7/03)

Active Subwoofer (Analog) - Analog Devices Application Notes  (app note added 2/06)

Active Subwoofer (Intersil) - Intersil Application Block Diagram  (app note added 3/06)

Advanced Audio Amplifier - This is roughly the minimum number of components that represents the classic audio amplifier topology. You can clearly see the three stages found in many audio amps (and op amps today). However, looking at actual audio designs, you'll find the basic topology has been tweaked and enhanced in a few key locations....(spice design added 02/09)

All About Audio Amplifiers - Amplifiers would be nothing without tone controls. They allow us to boost or cut the low and high ends of the audio spectrum. Nobody would buy an amplifier or preamp that did not have them. Because these controls are so important designers spend a lot of time and effort on these circuits.....(circuit design added 09/08)

All-Triode Direct-Drive Tube Amps for Electrostatic & Electret Headphones  - Two electrostatic headphone driver designs: the second is DC-coupled and uses high voltage Apex op-amps as DC regulators. They will drive Stax and Sennheiser electrostatic phones, and the author includes directions for adapting the designs to other models. These are "the best electrostatic headphone amplifiers currently available, anywhere in the world." Will also drive electret headphones. Recommended only....Designed by Kevin Gilmore  (circuit design added 04/05/06)

Altec 1566A:Vacuum Tube Preamp & Direct Box Project - There are all sorts of tube circuits, some of which actually deliver The Sound people associate with Vacuum Tubes.  Did you know, for example, that asymmetrical distortion generates even-order harmonics while symmetrical distortion produces odd-order harmonics?  Neither vacuum tubes nor transistors are exclusively responsible for either type of distortion, it’s really about circuit design. (added 4/02)

Amp with Tone Controls & Soft Switching - Built around an LM380, this amplifier includes tone controls and electronic "soft switching". The soft switching circuitry ensures power is built up gradually eliminating the dc thump…(added 07/07/07)

Amplified Ear - Useful to listen in faint sounds.  1.5V Battery operation.   (electronic circuit added 06/07/08)

Amplified Ear (drawn by R. Kollman) - This circuit, connected to 32 Ohm impedance mini-earphones, can detect very remote sounds. Useful for theatre, cinema and lecture goers: every word will be clearly heard. You can also listen to your television set at a very low volume, avoiding to bother relatives and neighbors. Even if you have a faultless hearing, you may discover unexpected sounds using this device: a remote bird twittering will seem very close to you. ….(electronic schematic added 11/08)

Amplifier (LM3886) - So what the heck is a Gainclone? Originally, the term Gainclone meant a clone of the 47 Laboratory Gaincard. The 47 Laboratory Model 4706 Gaincard is understood to have the following general features ...(electronic design added 7/08)

Amplifier 2x30W with STK465 - ….(circuit design added 03/08)

Amplifier Considerations in Ceramic Speaker Applications - Maxim App Note 4164  -- 2/05/2008 --  (app note add 5/08)

Amplifier of acoustic frequencies with preamplifier - Minimal signal of entry: 94mVp-p with preamplifier, 0,65Vp-p without the preamplifier….(circuit design added 08/08)

Amplifier removes common mode noise on RGB differential video transmission line - 04/13/06 EDN-Design Ideas: Use a single operational amplifier to minimize common-mode signals' effects on differential-component-video receivers.....(design idea added 10/06)

Amplifier Timer - Turns-off your amplifier when idle for 15 minutes.  Fed by amplifier tape-output.   (electronic circuit added 06/07/08)

AN Integrating CobraNet into Audio Products - (app note added 5/08)

An Outboard Digital-to-Analog Converter for Digital Audio Sources - AN-394 Analog Devices Application Notes  (app note added 7/06)

AN-106: A Collection of Amp Applications - AN-106 Analog Devices App Notes  (app note added 2/06) Examines Some of  Numerous and Widely Used Applications of  Operational Amplifier

AN-11 LX1720: High-Efficiency Class-D, Stereo Audio Amplifier Controller IC. Summary - Application Note Microsemi 1501 (added 2/07)

AN-137: A Digitally Programmable Gain & Attenuation Amplifier Design - AN-137 Analog Devices Application Notes  (app note added 2/06)

AN-16 AudioMAX Design Resource - Application Note Microsemi 1502 (added 2/07)

AN-211: The Alexander Current-Feedback Audio Power Amplifier - AN-211 Analog Devices Application Notes  (app note added 2/06)

AN213: CS4201/CS4202 Two Channel Audio Design - (app note added 6/07)

AN214: CS4201/CS4202 Six Channel Audio Design - (app note added 6/07)

AN-299: Audio Applications of Linear Integrated Circuits - National Semiconductor Application Note   (app note added 2/06)

AN-320B: CMOS Multiplying DACs & Op Amps Combine to Build Programmable Gain Amplifiers, Part 2 - AN-320B Analog Devices Application Notes  (app note added 2/06)

AN-345: Grounding for Low-and-High-Frequency Circuits - AN-345 Analog Devices Application Notes  (app note added 2/06) Know Your Ground and Signal Paths for Effective Designs. Current Flow Seeks Path of Least Impedance-Not Just Resistance....

AN-346:High-Performance Audio Applications of the LM833 - National Semiconductor Application Note   (app note added 2/06)

AN-347: Shielding & Guarding - AN-347 Analog Devices Application Notes  (app note added 2/06) How to Exclude Interference-Type Noise. What to do and Why to do it-A Rational Approach

AN-349: Keys to Longer Life for CMOS - AN-349 Analog Devices Application Notes  (app note added 09/08) Here's How CMOS Can be Protected Against Abuse

AN-35 LX1725 15W X 2 30W BTL Class-D Audio Amplifier - Application Note Microsemi 1504 (added 2/07)

AN-358: Noise & Operational Amplifier Circuits - AN-358 Analog Devices Application Notes  (app note added 2/06)

AN-359: Settling Time of Operational Amplifiers - AN-359 Analog Devices Application Notes  (app note added 2/06)

AN-384: Audio Noise Reduction & Masking - National Semiconductor Application Note   (app note added 2/06)

AN-386: A Non-Complementary Audio Noise Reduction System - National Semiconductor Application Note   (app note added 2/06)

AN-581: Biasing & Decoupling Op Amps in Single Supply Applications - AN-581 Analog Devices Application Notes  (app note added 2/06)

AN-583: Using the SSM2167 Evaluation Board - AN-583 Analog Devices Application Notes  (app note added 2/06) This document explains how  evaluation board is set up and how to use it to evaluate  SSM-2167.

AN-649: Using the Analog Devices Active Filter Design Tool - AN-649 Analog Devices Application Notes  (app note added 2/06)

AN-772: A Design & Manufacturing Guide for the Lead Frame Chip Scale Package - AN-772 Analog Devices Application Notes  (app note added 2/06)

AN-898: Audio Amplifiers Utilizing: SPICE Protection - National Semiconductor Application Note   (app note added 2/06)

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 the receiver section of Dave Johnson's Handbook of Optical Through the Air Communications.  (this link is off-site.) ….(designed by David A. Johnson)

Audio Amp Based on LM383 8 Watts (Aaron Cake) - (circuit added 7/02)

Audio amp makes efficient fan Controller - 11/09/00 EDN-Design Ideas: /.....(design idea added 12/00)

Audio Amp Output Power Limiter - (circuit / schematic added 6/03)

Audio Amplifier - This simple amplifier shows the LM386 in a high-gain configuration (A = 200). For a maximum gain of only 20, leave out the 10 uF connected from pin 1 to pin 8. Maximum gains between 20 and 200 may be realized by ...(electronic design added 7/08)

Audio Amplifier for PC - This is an audio Amplifier that it has MULTIinputs for MULTImedia use :-)  (added 10/05)

Audio Amplifier Output Relay Delay - This is a simple circuit which I built to one of my audio amplifier projects to control  speaker output relay. The purpose of this circuit is to control  relay which turns on  speaker output relay in  audio amplifier. The idea of  circuit is wait around 5 seconds after  power up until  speakers are switched to  amplifiers ....  (added 11/05)

Audio Applications of Linear Integrated Circuits - National Semiconductor Application Note   (app note added 2/06)

Audio Compressor - A circuit for a single-channel audio compressor using a JFET to control  gain of a virtual earth Amplifier. (added 4/02)

Audio equalizer features transimpedance Q enhancement topology - 03/06/08 EDN-Design Ideas: A novel op-amp configuration enables a graphic equalizer with a minimal number of amplifiers.....(design idea added 09/08)

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.

Audio Level Control Device - An automatic controlling device for sound levels implements the steps of: installing a 10 digit 7-segment on the noise measurement machine; controlling the Micom profit amplifier if an audio key was input into the Micom (added 6/07)

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....(schematic design added 6/07)

Audio level meter VU Meter - This circuit uses just one IC and a very few number of external components. It displays  audio level in terms of 10 LEDs. The input voltage can vary from 12V to 20V, but suggested voltage is 12V. The LM3915 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs  providing a logarithmic 3 dB/step analog display. LED current drive is regulated and programmable, eliminating  need for current limiting resistors….  (added 10/05)

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....  (added 10/05)

Audio Line Driver - (electronic schematic / circuit added 6/07)

Audio Noise Reduction & Masking - National Semiconductor Application Note   (app note added 2/06)

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….(added 05/05/05)

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...(added 04/05/06

Audio Spectrum Monitor - A digital audio signal processing experiment of real-time FFT (Fast Fourier Transform) analysis.  (added 10/05)

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....  (added 10/05)

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'....(circuit added 07/07/07)

AudioMAX Design Resource AN-16 - Application Note 16 from Microsem  (app note added 3/06)

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...(added 04/05/06)

Auto volume control - ….(electronic schematic added 08/08)

Automatic Loudness Control - Simple add-on module Switchable "Control-flat" option  (added 3/05)

Balanced Floating Output Stage Circuit  - A great output topology based on a design by George D Pontis  (circuit design added 08/08/08)

Balanced Low Noise Microphone Preamp - very low noise, close to  oretical minimum, high hum rejection and variable gain with a single rotary pot, similar to that used in many professional grade mixing desks (added 8/03)

Battery Powered Electret Microphone - Note: scroll down to this this circuit.  This circuit can be used with normal tape recorders and sound cards which usually are designed for dynamic microphones. When you build this circuit inside  microphone case (or to small external box) you can make yourself an universal microphone out of an electret capsule. (added 11/05)

Biasing & Decoupling Op Amps in Single Supply Applications - AN-581 Analog Devices Application Notes  (app note added 2/06)

Bidirectional 2.4 GHz One Watt Amplifier - (circuit / schematic added 6/03)

Bidirectional 900MHz One Watt Amplifier - This device is a stereo amplifier for a high sensitivity stereo parabolic microphone. It can be used for listening to distant sounds. Typical parabolic microphones are monophonic, this unit has a stereo audio path that helps produce more realistic sounding audio. The Big-E can be used with headphones or as an audio source for a stereo tape recorder....   (added 10/05)

Bidirectional 900MHz One Watt Amplifier qsl - (circuit / schematic added 6/03)

Binaural Mics - (electronic schematic added 8/02)

BJT Current Source - ...(spice design added 02/09)

Boost 3.3V to 5V with Tiny Audio Amplifier - 09/05/02 EDN-Design Ideas: This charge-pump circuit quietly converts a 3.3V source to 5V at 500 mA (figures 1 and 2). National's (www.national.com)LM4871LD power amplifier makes this design idea both possible and practical, thanks to its low output resistance, low cost, compact size, and high dissipation capability. Its output resistance has an average value of 0.....(design idea added 12/04)

Boundary Layer Dish Microphone - ideas for a directional microphone assembly (added 4/06)

Brute Force In A Line Stage (100% Tube!) - An OTL mu follower design. "One, often forgotten, purpose of the preamp is to drive headphones. I listen with a pair of AKG K240s, which is a relatively easy load to drive. This all-tube line stage and driver can power them, without resorting to output transformers."  Designed by Eric Barbour  (circuit design added 08/08/08)

Charging batteries with Solar energy 4 - Depending on the application, charging batteries can be complex process. Charging methods range from constant voltage to pulsed and random charging. Once power is being delivered back into the battery, you have to know when to stop charging!…(added 6/07)

Cheap 100 to 150 Watt Amp - Here is a simple and cheap amp to make. ….(circuit design added 11/08)

Cheap Audio Booster - ….(electronic schematic added 08/08)

Cheap DSP Experiments - Digital signal processing experiments with only a cheap 8bit microcontroller. This project experiments on Delay, Echo, Pitch Conversion, Filter and etc.  (added 10/05)

Chu Moy Headphone Amp - This is a Chu Moy headphone amp I made. I got the PCB design from Guzzler from Head-Fi and the original design is very popular and is here. I changed Guzzler's layout so I could use a Taiwan Alpha pot on the PCB. These pots a high quality (some say better than ALPS blue velvet) and are available from Jaycar. You can see the thread here. I also made a DIY Brown dog adapter so I could use two OPA627 single opamps in a dual opamp socket. ….(electronic schematic added 11/08)

Circuit Combines 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-known LM317, a low-cost power-supply regulator. Using this chip, you..../.....(design idea added 10/03)

Class A JFET Opamp Circuit - First Generation design... that means it is not our latest design.  (circuit design added 08/08/08)

Class A MOSFET Headphone Driver - You can't get much simpler than this classic class-A MOSFET driver. It's a single-ended design that is ideal for the electronics beginner, as well as for the audiophile who wants class-A MOSFET sound without the fuss. Build it in an evening and enjoy!  Designed by Greg J. Szekeres  (circuit design added 04/05/06)

Class A Power Amplifier Notes - These notes have evolved as a result of my long-time interest in both Hi-Fi music equipment and modern electronics. I am a keen audiophile, electronics DIYer and perfectionist, this mix constantly keeps me going. The page serves mostly as a memo that holds my working notes. However...(added 07/07/07)

Class A//A-B 100W Amplifier - A Class A // Class AB amplifier rated 100 Watts when driving a 4 ohm loudspeaker. (added 10/05)

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…(added 05/05/05)

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. ….(design added 11/08)

Class-D Audio Amplifier ICs - MicroNote 1503 from Microsem  (app note added 3/06)

CMOS IC Audio Oscillator - (electronic schematic / circuit added 2/07)

CMOS Multiplying DACs & Op Amps Combine to Build Programmable Gain Amplifier, Part 1 - AN-320B Analog Devices Application Notes  (app note added 2/06)

Collection of Amp Applications - AN-106 Analog Devices Application Notes  (app note added 2/06) Examines Some of  Numerous and Widely Used Applications of  Operational Amplifier

Computer Microphone - circuit by Lazar Pancic  -  adapting electret microphone to soundcards with dynamic microphone inputs(electronic design added 6/07)

Condenser MIC Audio Amplifier - (electronic Circuit / Schematic added 10/04)

Condenser Microphone Hookup - ASCII format (circuit added 7/02)

Crest Audio LT Series LT100 LT1500 & LT2000 SchematIC Set - A commercial Class D Amplifier, complete schematics in PDF format. (added 4/02)

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….  (circuit / schematic added 6/03)

Current vs. Voltage Feedback Amplifiers - National Semiconductor Application Note   (app note added 2/06)

Current-Feedback Myths Debunked - National Semiconductor Application Note   (app note added 2/06)

Death of Zen Doz a New Class a Power Amp - An ultra simple, high performance Class-A power amp. Revision-A boards now shipping  (circuit / schematic added 6/03)

Death of Zen Preamp - "Minimalist" preamp, designed to suit the DoZ (or any other) power amplifier  (schematic added 6/07)

Designing A Limiter For Headphone Amplifiers - Design principles and circuits for building opamp-based headphone amplifiers. This article reviews selection criteria, feedback configurations, capacitor coupling, RF shielding, output stage topology, short circuit protection, equalization, acoustic simulation, headphone distribution amplifiers and power supply options. Also discusses design with tube amp-blocks (AC feedback amplifiers and....  Designed by HeadWize  (circuit design added 04/05/06)

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 added 02/09)

Digital Nulling of Precision Op Amps - AB-3 Analog Devices Application Notes  (app note added 2/06)

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…(circuit added 6/07)

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…(circuit added 6/07)

Digitally Programmable Gain & Attenuation Amplifier Design - AN-137 Analog Devices Application Notes  (app note added 2/06)

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 reverse (volume decrease) operation of both channels.….(design added 08/08)

DN0001-MP7720-Using Split Supplies - Monolithic Power Systems, Inc Design Note (added 3/06)

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. ….(electronic schematic added 11/08)

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 .....(circuit added 07/07/07)

Dual Amp For Use with Opto Compressor Project - PCB.ZIP containing schematic and gerber files.   (circuit added 08/08/08)

Dual JFET-992/993 PCB schematic - (electronic circuit added 08/08/08)

Dual JT-MB-C Microphone Combining Circuit - AS053 Jenson Transformer Application Note  (app note 6/07)

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 sides 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..../.....(design idea added 4/02)

Dual Mike Preamp power supply Gerber - (electronic circuit added 08/08/08)

Dual Transformerless Class A Discrete Mike Preamp  - Uses JMP-1 Modules  (circuit design added 08/08/08)

Dynamic Microphone Amplifier - (circuit / schematic added 6/03)

Dynamic microphone to electret microphone input - Circuit which works as an preamplifier which allows you to replace an electret microphone with a dynamic microphone…..(electronic schematic added 8/02)

Electret Condenser Microphone Amplifier - microphone pre-amplifier for an Electret Condenser Microphone, pdf file

Electret Microphone Connection - how to connect electret microphone (added 4/02)

Electret Microphone Powering - (electronic schematic added 8/02)

ESP SIM Sound Impairment Monitor - a method of determining just how much your amplifier modifies the original signal (added 4/02)

Fender-Tone Tube Headphone Amplifier - This tube amplifier with sonic controls has a paralleled White cathode follower output stage for driving low impedance headphones. The sonic controls consist of a Fender tone stack (bass, mid and treble), and ambience and blend controls. Includes simulation files for use with OrCAD Lite software.  Designed by Alex Cavalli  (circuit design added 04/05/06)

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,....(Tony van Roon's electronic design added 6/07)

FXBus-an Effects Experimenter's Delight! - Like to build guitar effects? Want a cleaner way to experiment than perfboarding each new one? You'll love FXBus.….(circuit design added 04/05/06)

GAINCLONE - Gainclone is a single integrated circuit based on an operational amplifier (op amp) on a single substrate of silicon. The LM3875 is the "weapon of choice". This great chip, is a little larger than the size of a thumbnail and can deliver up to 56W RMS continuous with 100W ....(added 07/07/07)

Gainclone 2x68 Watt Full Amplifier - In this application, we are building a gaincard like amplifier. This application type is named gainclone in audio world. To take a satisfactory audio response, we are adding a Linkwitz equaliser to the feedback line and adding bass compensation also. We are using LM3886....(circuit design added 07/07/07)

Gainclone Amp - You read where the subjective reviewer tells of the equipment vanishing and revealing the music unfettered. Well for the first time with any of mine or anyone else's gear that this is what I hear. There are no speakers there is just the music. A soundstage projecting from the wall behind....(07/07/07)

Gainclone Amplifier - GainClones have VERY few components and this one is based on the National Semiconductor LM3875 IC. The PCBs and components are very simple and quick to make, only took about 20 mins to assemble both amps and rectifier board. DC offset was about 80mV on one channel and about 40mV...(added 07/07/07)

GainClone Amplifier 1 - The amp is based on the Project 19 PCB, so uses a pair of LM3876 (or LM3886) power opamps, run from a ±35V supply. I used a cut-down P88 preamp PCB because I only wanted one preamplifier stage, but the entire board can also be used. Alternatively,….(added 07/07/07)

Gainclone for the PC Age - Audio input comes from either the Line-Out of the PC or an external sound card (described later). A small filter consisting of 680Ω/47pF excludes any RF signals from entering the case. 470nF input capacitor should have a high voltage rating since it protects against line voltages being connected to the amplifier, since it is in the signal path it should be a high quality type....(circuit added 07/08/09)  designed by Malcolm Rix

General purpose 2 x 2 Watts power Amplifier - If you are a real electronics amateur, than you'll need a good audio power amplifier to be used in your endless experiments. Contents: Schematics, PCB's and photos.….(circuit design added 08/08)

Guitar Amplifier - ….(design added 08/08)

Guitar Amplifier 10 Watt - Old-Style ultra-compact Combo2-inputs-Overdrive-Treble-enhancement (added 9/04)

Guitar Fuzz Box - This circuit was designed to obtain a valve-like distorted sound from an electric guitar or other musical instrument. For this purpose a very high gain, three-FET amplifier circuit, was used. The output square wave shows marked rounded corners, typical of valve-circuits when driven into saturation. Therefore, the distorted sound obtained from such a device has a peculiar tone, much loved by most leading guitarists. ….(electronic schematic added 11/08)

Gyrator Filter Design Info for Single Amp EQ - The gyrator is used in place of the inductor in a LC filter. (circuit added 08/08/08)

Headphone (headbanger) Amplifier - After the euphoria over receiving my new Sony Minidisc bundle had partially subsided, I noticed that the portable unit, the MZ-E40, has a rather weak output. Measurements showed that it can only manage 80mV rms output and only about 74dB SPL output from the phones.....(electronic circuit added 1/03)

Headphone Amplifier - High Quality unit.  No need for a preamplifier.   (electronic circuit added 06/07/08)

Headphone Amplifier (Andy Collinson) - An amplifier to drive low to medium impedance headphones built using discrete components…(added 07/07/07)

Headphone Amplifier (PAGE 30) - Can be directly connected to CD players, tuners and tape recorders….(circuit added 9/04)

Headphone Listening Improver - The 'Super Stereo' effect of headphone listening is undoubtedly part of the experience for many of us, and adds to the listening enjoyment when listening is all we are doing. But when you just want background music to accompany, say the reading of a book, then the 'in your face' (or more accurately 'in your head') nature of full stereo is an unwanted distraction.…(electronic design add 6/07)

Headphone Monitor Amp - (circuit / schematic added 6/03)

Hi-End Transformer-Coupled Headphone Amplifier With Digital Input - A 2-stage transformer-coupled tube headphone amplifier with a DAC front-end. The amplifier can drive headphones of 300, 600 ohms impedance. The DAC is from a Crystal Semiconductor CS4390 evaluation board.... Designed by Andrea Ciuffoli  (circuit design added 04/05/06)

Hi-Fi Headphone Amp - The intention is to permanently insert the headphone amp between pre and power amps, although it can be used as a stand-alone item. The input relay is operated by auxiliary contacts on the headphone sockets through a transistor driver (with a small delay) so as to mute the power amp input when listening on headphones. (diagram added 6/03)

Hi-Fi Headphone Amplifier - Can be directly connected to CD players, tuners and tape recorders. * Tested with several headphone models of different impedance: 32, 100, 245, 300, 600 & 2000 Ohm. * Old 8 Ohm impedance headphones can be also driven, but these obsolete devices are not recommended. * Schematic shows left channel and power supply (common to both channels). * Numbers in parentheses show IC1 right channel pin connections. * A correct grounding is very important to eliminate hum and ground loops. Connect to the same point the ground sides of J1, P1, C2, C3 & C4. Then connect separately the input and output grounds to the power supply ground. ….(electronic schematic added 11/08)

Hi-Fi Headphone Amplifier (Richard Crowley) - This design for a headphone amplifier arose after the purchase of commercial equipment with separate pre and power amplifiers without a headphone output….(electronic design added 02/03/04)

Hi-Fi PC Speaker System - Standard LED VU meter, includes simple rectifier circuit for full wave detection  (electronic circuit added 4/05)

HiFi Preamp - The PGA2310 is a pretty neat chip. It's capable of attenuating a stereo source over a 127dB range (-95.5dB to +31.5dB) with 0.5dB steps. It has a maximum gain error of +/-0.05dB, and THD of 0.0004% at 1KHzS...(circuit added 04/05/06)

Hi-Fi USB Audio DAC - Regulator: This board supplies DAC board with +/- 15V for analog section. MUR860 in rectifier bridge, LM317 and Lm337 as regulator IC's and BG-STD at the output. LM317, LM337 power supply PCM2702: A little modified version of ....(circuit added 07/07/07)

Hi-Fi USB Audio DAC with PCM2702  - The heart of this circuit is low-cost 16-bit Philips DAC. As a SPDIF decoder was chosen Cirrus Logic CS8412 IC with SN75179 as an input driver....(circuit added 07/07/07)

High-End Audio Volume Control 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' potentiometers. Clearly, the IR remote control provides convenience over solutions with stepped attenuator rotary switches. The sealed relays will maintain contact quality over a practically endless lifetime. ….(circuit design added 11/08)

High-Performance Audio Applications of the LM833 - National Semiconductor Application Note   (app note added 2/06)

Infrared cordless Headphone Amplifier - (schematic added 09/08)

Inside Story: 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, their different functional parts look like a newspaper clip collection. If the amp ….(circuit design added 03/08)

Interfacing Microphones to Computer Sound Cards - (electronic schematic / circuit added 4/02)

iPod Super Dock Project (Part 1) - This one goes out to everyone that has an iPod or two laying about and an itchy soldering iron and thinks that the standard USB or Firewire dock just isn't quite good enough. The tiny thirty pin dock connector on the bottom of later model iPods contains quite a ....(circuit added 07/07/07)

iPod Super Dock Project (Part 3) - This one goes out to everyone that has an iPod or two laying about and an itchy soldering iron and thinks that the standard USB or Firewire dock just isn't quite good enough. The tiny thirty pin dock connector on the bottom of later model iPods contains quite a ....(circuit added 07/07/07)

iPod Super Dock Project (Part 4) - This one goes out to everyone that has an iPod or two laying about and an itchy soldering iron and thinks that the standard USB or Firewire dock just isn't quite good enough. The tiny thirty pin dock connector on the bottom of later model iPods contains quite a ....(circuit added 07/07/07)

iPod Super Dock Project (Part2) - This one goes out to everyone that has an iPod or two laying about and an itchy soldering iron and thinks that the standard USB or Firewire dock just isn't quite good enough. The tiny thirty pin dock connector on the bottom of later model iPods contains quite a ....(circuit added 07/07/07)

Isolated Telephone Interface - This circuit allows you to record audio from a telephone line into a tape recorder or computer soundcard. Most of the parts for this circuit can be scrounged from an old modem, with some work, it is possible to rewire the modem circuitry and use the old modem case....(electronic design added 6/07)

Jericho Horns - …(electroninc design added 04/05/06)

JFET Double Balanced Mike Preamp - Based on a design by Graeme Cohen AES Preprint #2106  (circuit design added 08/08/08)

JFET Mike Preamp using Jensen JE16 Input Transformer - (electronic circuit added 08/08/08)

JFET992/3 Summing Amplifier Circuit  - Summing buss and amplifier circuit for an Audio Console design  (circuit design added 08/08/08)

JFET-MOSFET Headphone Driver - This amplifier is based on the MOSFET headphone driver by Greg Szekeres. It has a JFET impedance buffer front-end and a choke-input power supply. The sound characteristic of the amplifier can be tuned by adjusting the low pass filter formed with the input capacitance of the MOSFET.  Designed by Richard Murdey  (circuit design added 04/05/06)

Jitter Detector Input  Part #1 of a 2 part schematic - (electronic circuit added 08/08/08)

Jitter Detector Output Part #2 of a 2 part schematic - (electronic circuit added 08/08/08)

Jitter Modulator - (electronic circuit added 08/08/08)

JLH Class-A Amplifier - The 1996 version using the specified transistors with +/-22V supply rails and a quiescent current of 2A has an approximate rms power output, into a resistive load, of 10W into 16ohm, 20W into 8ohm, 15W into 4ohm and 10W into 2ohm. For minimum distortion, ....(circuit design 08/08/08)

JLH Class-A Update - Tim is a professional musician (a classical concert pianist) and so I trust his subjective judgement when it comes to assessing the accuracy and realism of sound reproduction. Before Tim first contacted me, he had built a kit version of the 1996 design, which he had ....(circuit added 08/08/08)

Kitchen DHT 28.11.2004 - ….(design added 03/08)

Klauskorrektor I - The first phono stage ….….(electronic schematic added 03/08)

Klauskorrektor II - This regulated power supply was built as a simplified outboard version of a PSU in my first phono stage. Replacing hexfreds with tube rectifier eliminates the need for power-on sequencing. Chassis (salvaged from a hospital laser PSU) size is 180W*240D*100H mm with a 125W double-C core...(electronic design added 6/07)

KRELL KMA160 Class-A Mono Block Amplifier - KRELL KMA160 Class-A mono block amplifier. The output power is 160 Watts for 8 Ohms and 320 Watts for 4 Ohms loudspeakers. ….(electronic schematic added 11/08)

La Petite Audiophile - …(schematic added 08/08/08)

Leach Amp 120 Watt Power Amplifier -

270-Watt Double Barreled Amplifier published in Audio magazine (added 4/02)

Leach Superamp - Latest update of the "Low Tim Amplifier"   One amplifier builder found that the 2N5416 PNP transistors that he purchased were NPN. I have tested them and verified this. Two of the transistors are shown in the linked photo. They are identified by the letters ON surrounded by a circle, signifying they are products of ON Semiconductor. You can check... (added 4/02)

Line level Signal to microphone input adapter - 270-Watt Double Barreled Amplifier published in Audio magazine (added 4/02)

LM1875-20-W Audio Power Amplifier  - Sometimes there is need to convert line level signals to such signal that it can be connected to microphone input. Because the line level signals are typically in range of 0.5..2V and the microphone signals are in millivolt range, quite much attenuation is needed to match the signal levels. This means that typically you will need 40-50 dB of attenuation.  (added 11/05)

LM1876-Overture Audio Power Amplifier Series Dual 20-Watt Audio Power Amplifier with Mute & Standby Modes  - The LM1875 is a monolithic power amplifier offering very low distortion and high quality performance for consumer audio applications...(added 04/2002)

LM380 Power Audio Amplifier - National Semiconductor Application Note 04-Nov-1995 (app note added 4/02)

LM386 0,325W Audio Amplifier - The LM386 is a power amplifier designed for use in low voltage consumer applications. The gain is internally set to 20 to keep external part count low, but the addition of an external resistor and capacitor between pins 1 and 8 will increase the gain to any value from 20 to 200. ….(electronic schematic added 11/08)

LM386 Audio Amplifier - This simple amplifier shows the LM386 in a high-gain configuration (A = 200). For a maximum gain of only 20, leave out the 10 uF connected from pin 1 to pin 8. Maximum gains between 20 and 200 may be realized by adding a selected resistor in series with the same 10 uF capacitor. The 10k potentiometer will give the amplifier a variable gain from zero up to the maximum. ….(electronic schematic added 11/08)

LM3875 GAINCLONE - Gainclone is a single integrated circuit based on an operational amplifier (op amp) on a single substrate of silicon. The LM3875 is the "weapon of choice". This great chip, is a little larger than the size of a thumbnail and can deliver up to 56W RMS continuous with 100W peaks and it can do this at 0.05% distortion! Because they are DC amplifiers (DC coupling right through the amp) they can go all the way to 400kHz! The first chipamp I built was a pair of monoblocks. Though these are a little industrial looking, they deliver big time. ….(circuit design added 11/08)

LM3875 Gainclone Amp - You read where the subjective reviewer tells of the equipment vanishing and revealing the music unfettered. Well for the first time with any of mine or anyone else's gear that this is what I hear. There are no speakers there is just the music. A soundstage projecting from the wall behind and from the sides fills the room (7 x 8 x 2.5 m) with clear detail and multilayer texture and complex timbres. The setup consists of a NAD C542 CD Player, DIY Cotton ConneX interconnects (similar to the DIY Silver Interconnect Cables but with cotton insulation), the Synergy LM3875 amp and small two-way bookshelf speakers. Speaker cables are twin runs of oxygen free copper cable. I expect the amp to improve over the next weeks but for now I am stunned!

LM3875 Gainclone Amplifier - GainClones have VERY few components and this one is based on the National Semiconductor LM3875 IC. The PCBs and components are very simple and quick to make, only took about 20 mins to assemble both amps and rectifier board. DC offset was about 80mV on one channel and about 40mV on the other. I used the optional Ci capacitor in the national datasheet for the IC which reduced it to between 0-4mV: This is the capacitor I chose, its an Elna Starget (expensive). The case was MUCH more time consuming and difficult to make though. I bought all the aluminium from a scrap metal yard including the heatsink. I got my aluminium panels cut at a sheet metal shop as I cant make straight cuts with a hack saw. ….(design added 11/08)

LM3875 Gainclone Power Amplifier - This is a basic design with a single LM3875TF chip per side, and one shared toroidal transformer. I will be making two of these amplifiers simultaneously but with a few critical component differences. One is based on standard components, and one on premium components. There was a lot of deliberation on the type of transformer to get, particularly the secondary voltages. The concern here is the target load as, generally speaking, the higher the voltage, the less suited it is to drive low impedance loads (4ohms). I settled on 20 volt secondaries which I think is a good compromise, feeling that 18v is perhaps a little too low and 22v a little too high to get the max with a 4 ohm load whilst minimising output loss if using 8 ohms. The ability to run stable at 4 ohms is paramount to me to keep it open to different applications, and output wattage is relatively unimportant for this design. ….(electronic schematic added 11/08)

LM3876 GainClone Amplifier - The amp is based on the Project 19 PCB, so uses a pair of LM3876 (or LM3886) power opamps, run from a ±35V supply. I used a cut-down P88 preamp PCB because I only wanted one preamplifier stage, but the entire board can also be used. Alternatively, the P19 amp can be run at higher gain than normal, alleviating the need for a preamp at all. The down side of this is that the noise level will be higher, and background noise may be audible with efficient speakers and/ or very quiet surroundings. ….(electronic schematic added 11/08)

LM3886 Amplifier - When I fired it up for the first time, I was immediately surprised with how much power was available, the level of detail and the nice bass response. It sounded much better than I was expecting and much better than it should considering the simplicity and low cost. Initially, I thought it sounded a little bright, but after about 12 hours the sound became more relaxed. ….(design added 11/08)

LM3886 Gainclone 2x68 Watt Full Amplifier - In this application, we are building a gaincard like amplifier. This application type is named gainclone in audio world. To take a satisfactory audio response, we are adding a Linkwitz equaliser to the feedback line and adding bass compensation also. We are using LM3886 which is the revised version of its brother LM3875. These are the parameters that we are intereted in. Honestly this values are much more better than many of HI-FI amplifiers sold in the market. Especially it is hard to find 110dB signal to noise ratio. And another property is, when there is no input, this amplifier is quite like a dead. It is nearly impossible to hear any noise when you stick your ear to the speakers. ….(design added 11/08)

LM3886 Monoblock Gainclone Amplifier - This is a monoblock Gainclone amp based on a LM3886 IC which is more suited to 4 ohm loads. It will output 70 Watts into 4 ohms. This version also uses a very high capacitance PSU and a snubber. The case is made entirely out of recycled aluminum bought from scrap metal yards. ….(circuit design added 11/08)

LM3886 Power Amp with DIY Chassis - This is a simple chassis using just 4 aluminum panels and 2 heatsinks. Designed around dimensions to tightly pack in a LM3886 chip amp kit. The top and bottom panels sit in ridges cut into the heatsinks with a table saw, and then the front and back panels just bolt into the end fins. Rear panel fixings are held with M3 nut and bolts, and panels that join to the heatsinks are held by M4 bolts tapped directly into the heatsinks so no additional brackets are required. Heatsinks are 75 x 160 x 50mm with a 10mm thick base. ….(electronic schematic added 11/08)

LM4780 Gainclone Amplifier - This is design is very similar to the National Semiconductor BPA-200 (Bridge/Parallel Amplifier) which uses 4x LM3886 per channel and an input buffer. This is design is very similar to the National Semiconductor BPA-200 (Bridge/Parallel Amplifier) which uses 4x LM3886 per channel and an input buffer ….(electronic schematic added 11/08)

LM4780 Micro-Amp - Having decided to build an ultra-compact design, using a spare LM4780 seemed like an obvious plan. Having said that, I might choose a different IC if I didn't already have one to hand. The LM4780 contains two LM3886 dies (reference) giving 60 watts per channel, which is rather more than required this application. National Semiconductor make an enormous range of IC's with differing power levels and configurations, and there are plenty of possible candidates for this application, after all, we only need a few watts as this amplifier will principally be driving small speakers on the computer desk. ….(design added 11/08)

Loud Speaker Protection & Muting - Protect speakers from turn-on and turn-off transients and amplifier faults    (electronic schematic / circuit added 4/02)

Loudspeaker Protection - Something you should use in any amplifier, especially in discrete amplifiers, is loudspeaker protection. The first part is the DC detector. This circuit will trigger the Off output if DC is present on the audio lines. The input goes through a low pass filter and then through the diodes. If there's any DC on the lines it will turn on the two transistors who will then turn on Q3, which triggers the Off signal. ….(design added 11/08)

Loudspeaker Protection & Muting - Many hi-fi amplifiers and professional power amps (and loudspeaker systems) provide some of protection, either to protect the speakers from an amp fault, and/or vice versa. Some of these are implemented at a very basic level, for example the use of a 'poly-switch'. The poly-switch is a non-linear resistor, having a low resistance ….(electronic schematic added 11/08)

Low cost audio filter suppresses noise & hum - 03/02/06 EDN-Design Ideas: Passive filter requires no dc power.....(design idea added 09/06)

Low Cost Audio VCA has High Performance - 01/19/95 EDN-Design Ideas: The inherent matching between the two transconductance amplifiers in IC1 (Fig 1)facilitates a voltage-controlled amplifier (VCA)that offers high performance and low cost. The circuit's maximum input voltage is +20 dBu (dBu=dB referred to 775 mV rms). THD measures less than0.015%; noise, -70 dBu; and control-voltage feedthrough, -70 dB.....(design idea added 3/06)

Low cost intercom using transistors - .... (added 10/05)

Low impedance microphone Amplifier - The circuit is a microphone amplifier for use with low impedance (~200 ohm) microphones. It will work with stabilized voltages between 6-30VDC. If you don't build the impedance adapter part with T1, you get a micamp for higher impedance microphones.....(electronic schematic / circuit added 2/05)

Low Noise Balanced Microphone Preamp - A discrete front end makes this balanced microphone preamp very quiet, and it has excellent noise rejection.  Since the SSM2017 has been discontinued (sad but true), and if you can't get the INA217 this may be the ideal replacement…(added 8/03)

Low Pass Filter For FM 88-108 MHz - Filter used for eliminate unwanted harmonic frequency at second and third. Notch filter, Band Pass Filter (BPF), and High Pass Filter (HPF) sometime combined in constructing LPF design. Schematic below for FM Broadcast Lowpass Filter 88-108 MHz….(added 08/08/08)

Low Pass Filter Subwoofer Circuit - ….(design added 08/08)

Low pass filter-subwoofer filter - ….(design added 08/08)

Low Power Audio Amplifier Based on LM386 - (schematic added 9/02)

Low Power Op Amp   Audio Amp Intercom - The example below illustrates using an op-amp as an audio amplifier for a simple intercom. A small 8 ohm speaker is used as a microphone which is coupled to the op-amp input through a 0.1uF capacitor. The speaker is sensitive to low frequencies and the small value capacitor serves to attenuate the lower tones and produce a better overall response. You can experiment with different value capacitors to improve the response for various speakers. The op-amp voltage gain is determined by the ratio of the feedback resistor to the series input resistor which is around one thousand in this case... (electronic circuit added 7/03)

Low-Voltage Class-Tube Headphone Amplifier - This OTL design features a high-voltage power supply that is less than half of the one used in the author's first amp and most other tube amps, but without compromising performance.  Designed by Helmut Ahammer  (circuit design added 01/08)

LX1725 15W X 2 30W BTL Class-D Audio Amplifier AN-35 - Application Note 35 from Microsem  (app note added 3/06)

Making a Rugged Connectorized Microphone from a Panasonic Microphone Capsule - (electronic schematic added 11/02)

Marshall Professional MKII Guitar Fuzz - This is probably one of the most legendary fuzz pedals that has ever existed, and for good reason too! This thing can produce some completely saturated fuzz that is capable of slipping into feedback easily if you crank it up loud enough. I just can't…(added 04/02)

MCP2030 3 Channel Analog Front-End DeviceOverview - Microchip Application Note Published 16-Dec-05   (app note added 2/06)

Micro Spy with FETs - (Tony van Roon's schematic / circuit added 10/02)

Micro Spy with TTL - (Tony van Roon's schematic / circuit added 10/02)

Micro Spy with USW - (Tony van Roon's schematic / circuit added 10/02)

Microphone Circuit Test Oscillator - This unit would be mounted in a small plastic or preferably metal box, with a 9V battery, level control, a male XLR connector (same as on a mic) and a switch.  Current drain is low, since the circuit only uses one dual opamp.  There is no need for a high quality device, and a 1458 is all that is needed....(schematic / circuit added 2/07)

Microphone from a Speaker - A circuit to Impedance Match a Speakeras a Mike.  Speakers can make a Good Microphone for some applications.  Bigger Speakers may also have a Good Low Frequency Response.   Ever seen a 15 Inch Microphonethis Circuit will do it....(design added 12/08)

Microphone Mixer (Aaron Cake) - Designed for 3-dynamic microphones (added 04/03/02)

Microphone Polarity Tester - (electronic schematic added 8/02)

Midi Passthrough Circuit - (electronic circuit added 1/03)

Mike Mute - Designed by R.G. Keen.   (added 05/08)

Mike Pads & Other Small Gadgets - Includes Active Direct Box circuit (added 4/02)

Mike Preamp Power Supply with Phantom Power - Uses a single 48 VAC center-tapped transformer  (circuit design added 08/08/08)

Minature FM 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,....(Tony van Roon's electronic design added 02/03/04)

Mini Bench Amplifier - This mini audio amplifier will test the audio stages in amplifiers such as the front end of FM bugs. You can also use it on lots of our other projects as well as the output stages of radios. It is a very handy piece of test equipment and will make a perfect addition to your collection.....(electronic circuit added 4/05)

Mini Portable Guitar Amplifier - Can be fitted into a packet of cigarettes.  Also suitable as Fuzz-box (added 3/05)

Miniature Class A Amplifier - The philosophy behind this minimalist design has been explained by Flavio Dellepiane on his highly interesting site 1. I have myself written an article about this fleapower amp from Italy in the American magazine AudioXpress 2.  All relevant details…(added 05/08)

Miniature FM Transmitter - (electronic diagram added 6/03)

Miniature FM Transmitter #2 - (Tony van Roon's electronic Circuit added 03/06)

Miniature FM Transmitter #3 - (Tony van Roon's electronic Circuit added 03/06)

Miniature FM Transmitter #4 - (Tony van Roon's electronic Circuit added 03/06)

Miniature FM Transmitter #5 - (Tony van Roon's diagram added 08/09)

Miniature FM Transmitter #6 - (Tony van Roon's electronic Circuit added 08/09)

Miniature FM Transmitter #7 - (Tony van Roon's electronic schematic / circuit added 08/09)

Mini-box 2W Amplifier - Designed for self-powered 8, 4 & 2 Ohm loudspeakers.  Bass-boost switch.   (electronic circuit added 06/07/08)

Modification of Panasonic Backelectret Capacitor Microphone WM GOAT Digikey P9967 ND - This drawing describes the conventional hookup and option where FET is connected as source follower with3 wires to preamp. (added 4/02)

Monoblock Gainclone Amplifier - This is a monoblock Gainclone amp based on a LM3886 IC which is more suited to 4 ohm loads. It will output 70 Watts into 4 ohms. This version also uses a very high capacitance PSU and a snubber. The case is made entirely…(added 08/08/08)

MOSFET Amplifier - This amplifier evolved from the previous 6 transistor mosfet amplifier. That design was already so good there seemed no reason to look for improvements, but the high open-loop distortion at 20kHz and the resulting triangular 'error voltage' extracted suggested that the non-linear mosfe....(schematic design added 08/08/08)

MOSFET  Power Amp - DIY high power MOSFET amplifier200 Wrms 8 ohms -350 Wrms4 ohms (added 4/02)

Motorola Hi-Fi power amp - This is a very simple, low cost, Hi-Fi quality power amplifier. You can build it 5 ways, like it's shown in the table (from 20 W to 80 W RMS). ….(circuit design added 11/08)

MP3 Player - This is my MP3/AAC player project. The difference to most other players is that decoding is not done on a specialized IC (like VS1001), but directly on the microcontroller. It can play MP3 (all bit rates) and AAC (up to ~256 kbps) from SD card in real time. The project is work in progress.  (circuit design added 07/07/07)

MP3 Player with IR Remote Control - This MP3 player similar to iPOD shuffle that is based on the latest innovative BU9432 chip from RHOM. It features USB 1.1 / 2.0 Controller, MP3 decoder, system controller for loading MP3 files from a USB flash drive, USB hard drive, USB CD-ROM or USB DVD-ROM drive all in one chip. Once USB flash drive is connected, BU9432 automatically ….(electronic schematic added 11/08)

Multimedia Speaker - …(circuit added 05/08)

Multiple Feedback Bandpass Filter - ….(electronic schematic added 06/09)

Negative feedback design for Amplifiers  - how to modify a small class AB amplifier for low distortion and minimal power drain…(added 07/07/07)

No-Compromise OTL Tube Headphone Amplifier - The author achieves his quest for the ultimate headphone amplifier that offers the best possible sound without any compromises. Based on the same circuit topology as his "Top-Level" amplifiers, this version uses a Raytheon 5842....Designed by Andrea Ciuffoli  (circuit design added 01/08)

Noise & Operational Amplifier Circuits - AN-358 Analog Devices Application Notes  (app note added 2/06)

Non Complementary Audio Noise Reduction System - National Semiconductor Application Note   (app note added 2/06)

Nulling of Precision Op Amps - AB-3 Analog Devices Application Notes  (app note added 2/06)

OA-15: OA-15 Frequent Faux Pas in Applying Wideband Current Feedback Amplifiers - National Semiconductor Application Note   (app note added 2/06)

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 ....(circuit added 7/02)

One Watt 2.3 GHz RF Amplifier using a MRF2001 - (diagram added 6/03)

One Watt Class C Amplifier - (electronic circuit added 7/03)

OTP µC Controls Boomer Amplifier - 03/18/99 EDN-Design Ideas: PDF contains multiple circuits, scroll to find this circuit.....(design idea added 7/03)

Output Current Limiter - ...(spice design added 02/09)

Output Current Limiting - ...(spice design added 02/09)

Output Stage - ...(spice design added 02/09)

Output Transformerless Tube Headphone Amplifier - This OTL mu-follower design uses paralleled tubes (2 per channel) to minimize noise. It also makes an excellent preamplifier.  Designed by Kurt Strain  (circuit design added 03/08)

Output Voltage Limiter - ...(spice design added 02/09)

Output Voltage Limiting - ...(spice design added 02/09)

Overture Audio Power Amplifier Series Dual 20-Watt Audio Power Amplifier with Mute & Standby Modes  - The LM1876 is a stereo audio amplifier capable of delivering typically 20W per channel of continuous average output power into a 4 or 8 load with less than 0.1% THD+N.….(added 05/08)