Index

Project link pages
Power amplifiers

Professional audio amplifier circuit diagrams
Car amplifiers

Power amplifier accessories
Headphone amplifiers
Instrument amplifiers
Preamplifiers

Tube amplifiers
Mixers circuits
Differential/balanced input and output circuits

DI-box circuits

Microphone preamplifiers
Building microphone
Microphone accessories
HiFi preamplifers
Phono preamplifiers
Other preamplifiers
Audio controlling circuits

Equalizers and filters
Crossovers
Compressor/limiter
Guitar effect boxes
Vocal elimination
Noise limiter / noise gate
Misc effects

Surround sound
Digital audio circuits

Audio recording/playback

Measuring

Special equipments
Design ideas
Audio chips

Other related links

Audio circuits to build

The following links to circuit diagrams and building projects I have found from other web sites. I have tested only very few of them so there is no guaratee that those circuit will work as expected. I don't have more info on those projects than what you can download from those sites which have the circuits. If you have more questions about those circuits then please mail the questions directly to the person who has designed the circuit or to the people responsible for those web pages.

Project link pages

Analog Music Zone Guitar Effects Schematics - guitar effects, compressors, microphones and effects Rate this link
Audio Electronic Design - hifi circuit page in French Rate this link
Elliot Sound Products Audio Projects - mixture of basic and not so basic designs Rate this link
Pro Audio Equipment Schematics Page - Alan Garren's excellent listing of vintage gear schematics including API, UREI, Altec, RCA and more Rate this link

Power amplifiers

Low power (<30W)

2 Watt Amplifier - low distortion amplifier using discrete components Rate this link
3 Transistor Audio Amp (50 milliwatt) - Here is a little audio amplifier similar to what you might find in a small transistor radio. Rate this link
8 Watt Audio Amp - based on LM383 Rate this link
A HIFI class D audio power amplifier - The purpose of this site is to share a pulse-width modulating class D audio power amplifier design with the world, in order to involve people that have an interest in this kind of technology. This is in effect an "open source project", i.e. the design is open and free, and those that have the interest and ability, are encouraged to feed back back into the project. Rate this link
Build a Class-A Amplifier - This is an amplifier design made by Nelson Pass publishes at 1977. This amplifier gives out 20 watts per channel into 8 ohms, 24 watts into 6 ohms, and 28 watts into 4 ohms. The amplifier is powered from 120V AC power. Rate this link
Cheap thingies to help you make some racket - small amplifier circuits using many amplifier ICs, from few watts to 200W Rate this link
Emitter-follower-power-amplifier - very low power (110 mW) expereimental simple design Rate this link
Hiraga Le Classe A 20W Rate this link
Lidstr??m Improved ZEN i - class A FET amplifier Rate this link
Low distortion audio amplifier - ultra-low distortion 30W power amp Rate this link
Low Power Audio Amplifier - based on LM386 Rate this link
Power amplifier has transient rail-to-rail swing - special common-drain MOSFET-based power op amp circuit Rate this link
"Quick and Dirty" Audio Amplifiers - For those of you who like to experiment with audio circuits and would like a "quick and dirty" amplifier that frees you from having to figure out the biasing resistors, this article has two for you (and they run off 9 Volts too!). One uses an opamp and the other used a transistor. Rate this link
Sanken Hybrid Audio Power Amplifier Data - technical data and application circuits for 10-50W amplifiers Rate this link
Simple Class A Amplifiers - a 10W design by J. L. Linsley Hood Rate this link
The Pass Zen Amplifier - 10 Watts of Single-Stage Single-Ended Class A Rate this link
Death of Zen (DoZ) - A New Class-A Power Amp Rate this link
DoZ Headphone Amp: A New Use For The Class-A Power Amp Rate this link
25W Class-A Hi-Fi Power Amplifier Rate this link

High power (>30W)

50 Watt Amplifier - easy to build general purpose 50 watt amp Rate this link
60 Watt Into 8 Ohms Power Amplifier - a simple amp to build, uses commonly available parts and is stable and reliable Rate this link
Ampli MOSFET - DIY high power MOSFET amplifier 200 Wrms 8 ohms - 350 Wrms 4 ohms Rate this link
Ampli MOSFET 360W - This is a circuit for 360 W rms 8 ohms or 550 Wrms 4 ohms powerful amplifier. The plans are available in English and French. Rate this link
Bridge/Parallel Amplifier (BPA-200) Documentation - This document provides a 200W audio amplifier solution using multiple LM336s and and design concept to reach even higher output power levels. Rate this link
El-Cheapo - A Really Simple 60W Power Amplifier Rate this link
Korkeallatuinen stereovahvistin 2 x 220W - This is a builging plan for an audio amplifier with 2 x 220W output power. Text is in Finnish. Rate this link
P400 hi-fi high end audio power amplifier - amplifier with 382W to 8 ohms power rating, can drive speakers at 2-16 ohms range Rate this link
SDS Labs Schematics - solid state class A amplifiers Rate this link
Simple 200W amplifier Rate this link
Single Chip 50 Watt / 8 Ohm Power Amplifier - uses LM3876 hifi amplifier IC from National Semiconductor Rate this link
The Leach Amp - 120W power amplifier, latest update of the "Low TIM Amplifier", claimed to be a very good sounding design Rate this link
The Leach SuperAmp - 270 watt Double Barreled Amplifier published in Audio magazine Rate this link
The LM12 - chip which can be uased ot make simple 80W amplifier Rate this link
Vahvistin National Semiconductorin LM3886 piirill?? - Amplifier circuit which uses LM3886 IC. Text of this document is in Finnish. The article includes circuit diagram and circuit board design. The LM3886 is a high-performance audio power amplifier capable of delivering 68W of continuous average power to a 4Ohm load and 38W into 8Ohm with 0.1% THD+N from 20Hz-20kHz. Rate this link
Gainclone - A LM3886 based Gainclone amplifier with input buffer and phase inverter for bridge connection. The LM3886 delivers around 68 watts and peak power of 120 watts. Rate this link
TDA7294 - The TDA7294 is a monolithic integrated circuit in Multiwatt15 package, intended for use as audio class AB amplifier in Hi-Fi field applications (Home Stereo, self powered loudspeakers,Topclass TV). This IC datasheet gives example circuit for up to 100W amplifier using this IC. Rate this link
Cheap 100 to 150 Watt Amp - Here is a simple and cheap amp to make Rate this link

Professional audio amplifier circuit diagrams

Brystom Power Amplifiers Circuit Diagrams Rate this link
Crest Audio LT Series LT100, LT1500 and LT2000 Schematic Set - A commercial Class D Amplifier, complete schematics in pdf format. Rate this link
PSS Amplifier Layouts - full circuit diagrams of some of their PA amplifiers in their Rate this link
QSC Audio has Rate this link
Renkus-Heinz Schematics Rate this link

Car amplifiers

20 Watt Power Amplifier - designed to be used as car amplifier Rate this link
Car amplifier information and schematics Rate this link
Car Audio Schematics - car amplifiers Rate this link
Car tube pre amplifier Rate this link
Do It Yourself Car Amplifier - This article is for those who wants to make their own car amplifier. The basics of calculation will be discussed below. If you have understand it you will be able to make car amplifier based on Rate this link

Power amplifier accessories

A DC Fault Protection Circuit for Audio Amplifiers - circuit ideas how to replace traditional CD protection relays with MOSFETs Rate this link
Bridging Adaptor For Power Amplifiers - The bridging adapter shown in this article can make an amplifier produce almost 4 times the power for the same impedance - but beware of the pitfalls. Rate this link
Loudspeaker Protection and Muting Rate this link
Loudspeaker Protection and Muting Rate this link
Power Follower with Dinamic Current Source by Reinhard Haffmann - less wasted power than true class A but not as good sound Rate this link
Power Amplifier Clipping Indicator Rate this link
Soft Power On Tester for Amplifiers Rate this link
Speaker protector Rate this link

Headphone amplifiers

A DIY Headphone-Amplifier with Natural Crossfeed - The in-head localization phenomenon of the headphones does not please many people. A "natural" crossfeed from the right (left) audio signal to the left (right) transducer, with an appropriate attenuation and delay, will reduce most of the adverse symptoms of headphone listening considerably. Rate this link
An Acoustic Simulator for Headphone Amplifiers - a simple RC filter that creates a more realistic sound image in headphones by electronically mimicking spatial hearing with "shaded" interchannel crossfeed Rate this link
Build These Noise-Canceling Headphones - plus Binaural Microphone Headset, Audio Probe, and Parabolic Microphone Rate this link
Designing an Opamp Headphone Amplifier - This article has design information and many circuit examples Rate this link
HeadBanger Headphone Amp Construction Kit Rate this link
Headphone Amplifier - designed for Sega Megadrive, but can be used with other line level signal sources, Originally published in ETI, December 1994 Rate this link
Headphone Amplifier from SDS Labs - uses a push-pull Class A MOSFET output stage, being driven by an op-amp Rate this link
HeadWize Projects - many headphone amplifiers and related circuits Rate this link
Kumisa Mk. II - DIY headphone amplifier project using AD844 and some special transistors Rate this link
Mapletree Audio Designs (MAD) Ear+ Stereo Headphone Amplifier Kit - This tube headphone amplifier kit manual has building instructions and full circuit diagram of this device. Rate this link
QRV-04 - The high performance SMD headphone amplifier - Cute SMD headphone amp designed especially for OPA134, OPA627 and AD8610 plus a buffer BUF634. Rate this link
SDS Labs Headphone Amp - solid state amplifier Rate this link
Top-Level OTL Tube Headphone Amplifier Rate this link
Ultra Simple Headphone Box - Here is a very simple passive headphone box that works really good and can drive many headphones. You have to rely on the power of your power amp or your headphone out of your amp or your mixer headphone out to power it. Because there are no active components, there is very little that can go wrong with it and it is very quick to make. Because there are no potentiometers, you are not able to adjust the individual volumes of each headphone. Rate this link

Headphone amplifier accessories

HJ-4P Professional headphone distribution box - drives up to 4 headphones from a single amplifier, has volume control and mono switch, product datasheet with circuit diagram in pdf format Rate this link
HJ-6 Standard headphone distribution box - drives up to 6 headphones from a single amplifier, product datasheet with circuit diagram in pdf format Rate this link

Instrument amplifiers

100W Guitar Amplifier - Guitar amplifiers are always an interesting challenge. The tone controls, gain and overload characteristics are very individual, and the ideal combination varies from one guitarist to the next, and from one guitar to the next. There is no amp that satisfies everyone's requirements, and this offering is not expected to be an exception. This amp is rated at 100W into a 4 Ohms load, as this is typical of a "combo" type amp with two 8 Ohm speakers in parallel. Rate this link

Preamplifiers

Historically, the job of a pre-amp was to boost incoming signal levels from your turntable or tuner to drive the the amp powering your speakers, and also to provide some switches and knobs for functions like volume control, source selection, and perhaps tone control. Nowadays you might sometimes see terms "passive preamplifier" or "passive linestage" and wonder what it means. Here is the description what they are: A passive linestage is an unpowered device typically located between the source components and the power amplifier/s. Because it is in the position which would otherwise be occupied by a preamplifier, and because it performs many of the same duties as a preamplifier, it is often referred to as a passive "preamp" although that term is not really accurate. Actually, the term "passive preamp" is slightly misleading. The word preamp or preamplifier is not supposed to be a passive device, as a passive device may not provide amplification. So a better term than passive preamp would be passive volume control or passive control center. The attenuator is enough for many uses, because with modern CD players and other sources providing sufficient output level to drive an amp to full output, a pre-amp doesn't necessarily need to provide gain anymore. Almost all modern audio source components (CD, DVD, tuner, DAT, etc.) will output a signal which is more than capable of driving a power amplifier. Volume control and source selection are still important, though. The passive preamplifier is a device that provides the gain control (variable attenuator controlled by potentiometer or switched resistor network) and source selection (set of switches). It may also include other features such as balance, muting, tape monitor selection, record out signal selection, channel switching, stereo/mono selection, channel reversing, headphone output, etc. Passive preamps have gained popularity in high-end audio circles. Provided that a high quality volume control is used, a passive preamp is often the easy and cheap way to reach high-end sound quality. Obvious advantage of parrive design is that there is no active or non-linear components no circuits, therefore no distortion! Unfortunately there tends to be a high output impedance and high capacitance.

ALL-FET MC phono preamp - phono preamp with 54 and 64 dB gain and RIAA accuracy is better than 0.2dB, from Rate this link
A Pocket Headphone Amplifier - This is a portable headphone amplifier for testing purposes using Burr-Brown OPA134 opamp in a non-inverting configuration, powered with 9V battery. Rate this link
A Transformer Coupled Linelevel preamplifier by Thorsten Loesch - This is a very simple tube based line stage. Rate this link
Audio Preamp - simple preamp for electric guitar or microphone Rate this link
Basic Passive Linestage - A passive linestage is simple to build and makes an excellent first audio project. Building one is a good way to practice soldering skills and construction techniques, and as no power supply or active components are required it is also a safe project for beginners. Rate this link
DACT Passive Preamp Document Rate this link
Driving The Power Amp: A simple line stage preamplifier project - Thos document describes one passive preamplifier design and some tube based preamplifier designs. Rate this link
Equalized Passive Preamplifier Rate this link
Hi-Fi Preamplifier Rate this link
High-Performance Audio Applications of The LM833 - RIAA phono preamplifier stages and active crossover networks Rate this link
High Performance Passive Linestage Rate this link
Hiraga MC -Moving Coil f?rst?rkare Rate this link
Kaneda Linjef?steg - includes phono and line inputs Rate this link
Mic-Pre Pan Pot Circuit Rate this link
Passive Linestages Rate this link
Preamplifiers - This site provides many preamplif?er plans Rate this link
Simple Car Preamplifier and Artificial Earth Rate this link
Simple Guitar Preamplifier Rate this link
The TNT Pressive?: A DIY passive preamplifier Rate this link
Vanhat vinyylilevyt CD-levyiksi tai MP3-kapetiksi RIAA-korjaimen avulla - This is a simple RIAA preamplifier that can be plugged to a PC soundcard. The text of this document is in Finnish. Rate this link
An experimental RIAA preamp using no capacitors in the direct signal path - The purpose of this report is to describe an experimental RIAA phono preamp that uses several different concepts to derive a high quality RIAA compensated phono preamp. Traditional RIAA compensation is done by way of resistors and capacitors to shape the frequency response. There are alternatives that use L-C-R networks to derive this compensation. In this preamp, we will use L-R only networks. The preamp uses unusual tubes. Rate this link

Application notes and datasheets

Power Amplifier Design Guidelines Rate this link
LM12CL - very compact IC for making good quality 80W audio amplifier, this IC has been used in some high quality active loudspakers Rate this link

Tube amplifiers

A hybrid amplifier using a 5687 tube and Magnatec PowerMosFets Rate this link
Ampage - tube amps and music electronics Rate this link
Bob's Music/Vacuum Tube Audio / Electronics page - many amplifier circuits Rate this link
Car tube pre amplifier Rate this link
Dynaco Mark 3 Rate this link
Dynaco stereo 70 Rate this link
Get more power with a boosted triode - Even though 6L6 beam-power tubes have been around for 66 years, they are still quite popular for use in electric-guitar amplifiers, and its cousin, the 6CA7 (EL34) power pentode, is a favorite among audiophiles. This design idea shows the 6L6 connected as a pentode, a true triode, and a "boosted triode," respectively. The boosted-triode configuration allows pentodes to produce pentodelike power while operating in a true-triode mode. Rate this link
Klassiskt 300B slutsteg Rate this link
Klaus Schiffer's audio web site - tube amplifiers and tube information Rate this link
Les projets en cours - tube amplifiers Rate this link
Musical Instrument Tube Amp Building, Maintaining and Modifying FAQ Rate this link
Pure A class - 15W pure A class and push-pull Rate this link
SDS Labs Schematics - solid state class A amplifiers, headphone amplifier, vacuum tube amps Rate this link
Sheldon's Audio Designs - audio DACs and tube amplifiers Rate this link
Traynor Amplifier Schematic Archive Rate this link
Vintage Quad equipment circuit diagrams Rate this link
Quad 22 - circuit diagram of commercial tube amplifier Rate this link
2 x 40 W Valve amplifier with active grid biasing - In this document you will see that the amplifier is built with only 5 vacuum tubes. The circuit is a classic push-pull amplifier using an output transformer with a center tap. This topology is widely used for tube amplifiers. Rate this link
40 Watt Tube Guitar Amp Rate this link
Building a Champ out of Junk Parts - This is a modification of original schematic from the 60's of a "Blackface Champ" tube guitar amplifier. Both original and modified version versions are shown. Rate this link

Tube amplifier related circuits

Phantom Power Supply Circuit - A power supply for adding 48 volt phantom power to microphone preamps Rate this link
Regulated 12 Volts DC Power Supply for Vacuum Tube Heaters - this 7812 based circuit circuit can be used with low-hum audio applications such as microphone preamps and for other applications that require well regulated 12 volts Rate this link
Regulated Vacuum Tube Power Supply - outputs regulated 250-300 VDC Rate this link

Mixers circuits

6 Input Mixer - 3 line inputs and 3 mic inputs Rate this link
DACS (distributed audio control system) - description of the design of a digitally controlled distributed mixing system Rate this link
High Quality Sound Mixer - very ambitious and expected to be very expensive mixer project, modular design Rate this link
Microphone Mixer - designed for three dynamic microphones Rate this link
Rane MP 24 Mixer Service Manual - This service manual includes the the device circuit diagrams. Rate this link
Simple audio mixer for two signal sources Rate this link
Single capacitor powers audio mixer - micropower 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 Rate this link
Stage and Recording Mixer - full featured modular mixer design Rate this link
Stereo Mixer - can mix four separate audio inputs to one mono or stereo output signal Rate this link
Simple Line Mixer and Patchbay - Make a simple line mixer to run the sound modules through in the studio. This mixer as simple as possible because of the time factor, and also to avoid unnecessary noise that a more complex design could create. It consists of 5 stereo inputs to plug in 5 stereo sound modules and a stereo out with volume controls. Rate this link

Mixer circuit parts

A Two-Channel Noise Gate - Analog Devices application note AN128 Rate this link
An Unbalanced Mute Circuit For Audio Mixing Channels - application note in pdf format Rate this link

Differential/balanced input and output circuits

Input

A New Balanced Audio Input Circuit for Maximum Common-Mode Rejection in Real World Environments - 109KB PDF file Rate this link
Audio Transformers - notes on using audio transformers for balanced signal interfacing Rate this link
Additional RFI Protection for Line Input Circuits - 8KB PDF Rate this link
External Isolation Transformer Box for Mackie (and other) Mixers Eliminates RFI Problems Rate this link
High CMRR Balanced Interface for Crystal 18 or 20 Bit A/D Converters - pdf file Rate this link
Internal Modification to Mic Inputs of the Mackie 1604 Mixer Eliminates RFI Problems Rate this link
JT-6110K-B at Input Stage for Crystal A to D Converters - high performance transformer balanced input stage for Crystal A/D converters, pdf file Rate this link
JT-11P-1 Balanced Tube Line Input Stage Rate this link
JT-11SSP-6M as Input Transformer for Crystal CS5367 A/D Converter - transformer balanced passive input circuit for CS5367 A/D converter, pdf file Rate this link
JT-16-A Improves Performance of SSM2015 Mic Preamp IC Rate this link
JT-16-A Improves Performance of SSM2017 Mic Preamp IC Rate this link
JT-MB-C in Low Noise, High Isolation Line Receiver for Low-Z Sources Rate this link
JP-11P-1 Input transformer improvement for electronically balanced input Rate this link
Jensen Transformers Application Schematics - many circuit examples with transformers Rate this link
JT-MB-C Isolates both Mic and Line Inputs of Inexpensive Mixer Rate this link
JT-MB-C Mic Input Isolation for Mackie Mixers Rate this link
JT-MB-C "Real" Mic Inputs & Phantom Power for Sony DAT Rate this link
Making Differential Probes - for sensing audio signal voltages across devices which are not ground referenced Rate this link
Subtleties count in wide-dynamic-range analog interfaces - article on balanced input designing with some example circuit topologies, Rate this link

Output

12 dB Amplifier and High Current Line Driver with DC Servo Rate this link
20 dB Amplifier and High Current Balanced Line Driver Rate this link
Driving a balanced line, and getting 3 signals down 2 lines! - Often we get asked "How do you drive a signal down a 600 ohm balanced line", or "How do I terminate a 600 ohm circuit". This is actually VERY easy to do, and all you need is an isolating transformer at each end, and some cheap op-amps to drive / receive the signal, along with a few resistors etc. Rate this link
High Output Line Driver for Single Ended Power Supply - pdf file Rate this link
JT-11-BM High Level Differential IC Output Stage with DC Servo Rate this link
JT-11-BM High Level High Current Differential Output Stage with DC Servo Rate this link
JT-123-S Line Driver with Feedback Around the Transformer Rate this link
JT-123-BL High Level Low Impedance Differential Output Stage with DC Servo Rate this link
Low Noise version of High Level Output Stage in 1031 - pdf file Rate this link
Mixed feedback drive circuits for audio output transformers - using feedback eliminates transformer distortion and primary resistance Rate this link
Simple 0 to 24 dB Gain Amplifier and Balanced Line Driver - 18KB PDF Rate this link

Input and output in same circuit

Balancing Acts - balanced and unblanced interface circuits using tubes Rate this link
Balanced Line Driver & Receiver Rate this link
Balanced Line Inputs/Outputs for Silicon Graphics Workstations - balancing using transformers Rate this link
Bridging Line Amplifier - transformer balanced input and output with amplifier in between Rate this link
Line-level transformers in High-End Audio - discussion on using audio transformers in equipment interconnections Rate this link

Other circuits

Grounding and shielding in balanced inputs and outputs which are transformer coupled Rate this link
JT-11-YZPC in Unbalanced Long Line Driver/Isolator Rate this link
Long Lines Driver - high current output configuration is ideal for use as a transformerless long lines driver Rate this link

DI-box circuits

DI-box is an electronic device for helping to interface electronic music instruments (like electric guitar and syntetizer) to mixing desks. DI boxes are used to connect instruments, e.g.bass, keyboards, directly to the console, i.e. without using a microphone. They can be passive (containing no powered electronics) or active (with powered electronics) and they are usually fitted with ground lift and pad switches. DI-box is designed to transfer the sound of your instrument to the mixing console, adding nothing and taking away nothing. The function of DI box is to convert an unbalanced, high impedence source, to abalanced, low impedence source for improved noise immunity and toavoid degradation from long (more than few meters) cable runs.The output of the DI box is connected to the balanced microphoneinput of the mixing desk. One of the most important things a DI has to do is create a balanced signal from anunbalanced signal. Typical terms you will see are "transformer balanced" and"actively balanced." The result is a balanced, low impedance sendthat can travel down a snake without coupling all manner of noise on aline or instrument level signal. Typical keyboard or other musical instrumentsuplies a low impedance, but unbalanced output (which is prone to pick upnoise on long runs).Generally DI box takes an unbalanced input and (withvarying amounts of isolation depending upon the box) provides a balancedline. It may also provide other functions - ground lifts, gain pad, etc.Many DI boxes provide also ground isolationwhich helps you to get rid of humming caused by ground loops(Hum and buzz are often caused by a connection between the mixer and ground at the guitar system.)DI-box can be used as a "splitter" when you plug (say) a guitar pickupin one 1/4" unbalanced jack and 1 /4" unbalanced patch to the guitar ampinto the other.

General information

A Direct Box can be inDIspensible - DI-box converts high impedance signal to a low impedance and converts unbalanced signal to balanced Rate this link

Transformer isolated DI box designs

AV-1 Tech Sheet (Direct box) - DI-box product datasheet which includes full circuit diagram, has line level and speaker level inputs, pdf file Rate this link
AV-1PV Tech Sheet - DI-box with line level and speaker level inputs, with input volume control, data sheet with circuit diagram, pdf file Rate this link
CB-1 Direct Box - unixersal DI-box product which works with guitar and keyboards, product datasheet with circuit diagram in pdf format Rate this link
DB-1 Direct Box - DI-box with instrument and speaker level inputs, product datasheet with circuit diagram in pdf format Rate this link
DB-4 Direct Box - four channel DI-box with keyboard or dum machnine inputs, product datasheet with circuit diagram in pdf format Rate this link
Direct Injection Box for Recording & PA Systems - passive and active DI-box designs Rate this link
Jensen Direct Box Transformers - data sheets have example circuit diagrams Rate this link
JT-DB-E Standard Musical Instrument or Synthesizer "Direct Box" Rate this link
JT-10KB-D Isolates and Converts Speaker Drive to Line Level Rate this link
JT-11-FL provides Isolated Line Output from Guitar Amplifier Rate this link
JT-11-FL Isolates & Converts Guitar Amp Speaker Out to Line Output Rate this link
JT-11P-1 Conversion of Unbalanced Input to Balanced Rate this link
JT-DB-E Full-featured "Direct Box" Application Schematic Rate this link
JT-DB-E "Direct Box" for Very High Level Signals - takes high level line signal and outputs balanced microphone level signal Rate this link
JT-DB-E Standard Musical Instrument or Synthesizer "Direct Box" Rate this link
Tillverka din egen DI-box - This document tells you how to build a transformer isolated DI box. The text in this document is in Swedish. Rate this link

Active Di box designs

Direct Injection Box for Recording & PA Systems - passive and active DI-box designs Rate this link
Electric Crayons, Anyone? (A Vacuum Tube Microphone Preamp / Direct Box Project) - published in January97 EQ Column Rate this link
Mike Pads and Other Small Gadgets - includes Active Direct Box circuit Rate this link
JT-11B-1 + "Phantom" Buffer Provide Balanced Guitar Output Rate this link

Signal splitters

JT-11P-1 in 4-Way Active "Guitar Splitter" - from one guitar to up to 4 guitar amplifiers Rate this link
JT-10B-D Used in Line Level 2-Way Splitter/Isolator - active line level splitter circuit with input and output isolation Rate this link
JT-11P-1 in 2-Way Passive "Guitar Splitter" - from one guitar to two guitar amplifiers Rate this link
MS-2 Mic Splitter - send signal from one microphone to two mixers, product datasheet with circuit diagram in pdf format Rate this link
MS-82P Microphone Splitter with Phantom Power Buss - 8 channel microphone splitter which can inject phantom power to microphone, product datasheet with circuit diagram in pdf format Rate this link
Theory and Construction of Mic "Splitters" - 5 page booklet in pdf format Rate this link
Transformer Coupled Splitter - active amplified transformer isolated signal splitter that enables hum-free connection of one guitar to more than one amp as well as having a direct output Rate this link

Signal isolation boxes

IT-1 Inline 600/600 ohm line transformer - audio signal isolation transformer, product datasheet with circuit diagram in pdf format Rate this link
IT-4 four channel isolation transformer unit - audio signal isolation transformer, product datasheet with circuit diagram in pdf format Rate this link
JT-11-DM Basic Hum Stopper Transformer isolation box - simple isolator for 600 ohm balanced audio lines Rate this link
JT-11P-1 Unbalanced Automotive or Consumer Application - isolation transformer box for unbalanced consumer audio line signals Rate this link
JT-11P-1 Conversion of Unbalanced Input to Balanced Rate this link
JS-11SSP-6M 150 ohm line to 600 ohm load application - isolation transformer with impednace conversion Rate this link
JT-11SSP-6M 600 Ohm Line Isolation Application - isolation transformer for 600 ohm balanced audio line Rate this link
JS-11SPP-6M 600 ohm line isolator with line termination switch - for used with long 600 ohm lines which need termination Rate this link
JT-11SSP-6M Universal Patchbay Isolation Application - for use with professional low impedance sources and high impedance loads Rate this link

Signal combining

Dual JT-MB-C Microphone Combining Circuit - connect two microphones to one microphone input Rate this link
JT-11SSP-6M Passive Stereo Matrix for M-S Mic Technique Rate this link
MC-2 Microphone Combiner - product datasheet with circuit diagram in pdf format Rate this link
Simple line mixer - mix two line level sources to one signal, includes separate volume controls for both signals, passive circuit Rate this link
Simple two line output combiner - convert consumer equipment stereo signal to mono or combine audio signal from two different equipments to one input Rate this link
Stereo to Mono Combiner for Balanced Systems Rate this link

Conversion between professional and consumer equipments

Interconnection of Balanced and Unbalanced Equipment - 4 page booklet in pdf format Rate this link
JT-10KB-D & JT-DB-E Provide "J-Box" Consumer to Studio Interfaces - from -10dBV unbalanced to 150 ohm balanced microphone level (-45dBu) signal and from +4dBu balanced signal to -10dBV unbalanced signal Rate this link
JT-10KB-D & JT-6110K-B "Pro" to "Consumer" Interfaces - from +4dBu balanced output to -10dbV consumer equipment input Rate this link

Other related circuits

Grounding and Shielding - describes basic audio transformer uses like balanced in/out and signal splitters Rate this link
Internal Modification to Mic Inputs of the Mackie 1604 Mixer Eliminates RFI Problems - adding transformer isolation increases common mode rejection and eliminates RF interference, pdf document Rate this link
Jensen Transformers Application Schematics Rate this link
JT-11P-1 as "Phase Splitter" with Symmetrical Outputs Rate this link
JT-10KB-D Isolates and Converts Speaker Drive to Line Level Rate this link
JT-11P-1 used as Unbalanced Polarity Inverter Rate this link
JT-11-DM Converts Unbalanced Output to Balanced Rate this link
JT-11SSP-6M Bi-directional Lo-Z Long Line Application - this circuit isolated and impedance matches under 100 ohm source to long cable line and that to over 10 kohm input Rate this link
JT-6110K-B Isolates "70 Volt" Line and Converts to Line Level Rate this link
JT-DB-E Converts Consumer Stereo Inputs to Mono Balanced Mic Output Rate this link
JT-MB-C Isolates both Mic and Line Inputs of Inexpensive Mixer Rate this link
JT-MB-C "Real" Mic Inputs & Phantom Power for Sony DAT Rate this link
JT-MB-C Mic Input Isolation for Mackie Mixers Rate this link
JT-MB-D Converts 600 Ohm Unbalanced Mic to 150 Ohm Balanced Mic Line Rate this link
Mixed feedback drive circuits for audio output transformers - technical paper from Rate this link

Microphone preamplifiers

A mic preamp boosts the very sensitive low level (millivolts) audio signal from a microphone to a more usable level, called "line level" (typicaly from 0.1V to few volts). The mic level signal can easily be degraded by cable length, cable capacitance, and other such things. A line level signal is vastly more robust, and is the levelused to ship audio around from consoles, toprocessing equipment, to recorders or amplifiers.Typical microphone preamplifier needs to produce around 40-60 Db of gain(what is needed depends on microphone and sound level). Usually microphone preaplifiers have gain adjust option in them.

2-wire Remot Microphone Amplifier - uses special amplifier module from Rate this link
Amplified Ear - Useful to listen in faint sounds 1.5V Battery operation, includes electret microphone preamplifier which runs from 1.5V DC and can directly drive 32 Ohms impedance mini-earphones Rate this link
A Vacuum Tube Microphone Preamp / Direct Box Project - from January 1997 EQ Column, includes Rate this link
Balanced mic/line amp with TUBES - uses two 12AU7 tubes in a class-A cathode-driven input stage, followed by a class-AB1 cathode follower output stage, 6db gain, requires 90VDC and 12VDC Rate this link
Balanced Microphone Preamp Project - simple preamplifier with phantom power Rate this link
Condenser microphone hookup Rate this link
DIY Speaker Testing Microphone - One problem most people have when starting to test their speakers using computer-based testing software and hardware is the mic. The mic is arguably the most important piece of the process, but the availability of high-quality, commercial mics with relatively flat response from at least 20hz to 20khz is low and those that are available are quite expensive. The whole process for building this mic yourself should take under an hour, but you'll need a few things. Rate this link
Dual Phantom Power Microphone Preamplifier - information and full schematic of a kit available from Rate this link
ECM Mic Preamplifier - low noise electret microphone preamplifier Rate this link
Electric Crayons, Anyone? (A Vacuum Tube Microphone Preamp / Direct Box Project) - published in January97 EQ Column Rate this link
IC mic preamp uses Jensen Twin-Servo topology Rate this link
Intercom preamp - a convenient way of making an intercom is to use a loudspeaker as a microphone Rate this link
Jensen Transformers Application Schematics - includes many microphone preamplifier related circuits Rate this link
JT-13K6-C in Simple One IC Stage Mic Preamp - 15KB PDF Rate this link
Kondensaattorimikrofonin esivahvistin - simple preamplifier for electret microphone, text in Finnish Rate this link
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. This circuit can be also adapted for higher impedance microphones (instructions for this are given). Rate this link
Low Noise Balanced Microphone Preamp - very low noise, close to the theoretical minimum, high hum rejection and variable gain with a single rotary pot, similar to that used in many professional grade mixing desks Rate this link
Low Noise Microphone Preamplifier Rate this link
Mic-Pre Pan Pot Circuit Rate this link
Microphone preamp - very simple two transistor circuit Rate this link
Mu Stage Tube Mic Pre - microphone preamp based on a Jensen transformer and an Alan Kimmel designed "Mu-mode" gain stage Rate this link
PAiA Tube Mic Preamp Rate this link
Portable Microphone Preamplifier - This circuit is mainly intended to provide common home stereo amplifiers with a microphone input. This 9V battery powered amplifier circuit is based on a low noise, high gain two stage PNP and NPN transistor amplifier, using DC negative feedback. Rate this link
Preamp for low-Z microphones - This is a low input impedance, high quality pre-amplifier of the sort that could be used in a stage mixing desk. This circuit is built using diescrete transistors and uses a dual rail power supply. Rate this link
Rane MS 1b microphone preamplifier circuit diagram - This is a circuit diagram of a commercial high quality balanced microphone preamplifier. This document is in pdf format. Rate this link
Simple microphone preamplifier - simple one transistor circuit Rate this link
Standard Microphone Preamplifier Input Circuitry - pdf file Rate this link
Vintage Neve Class A Circuit Information - Neve BA283AV Class A Preamaplifier Circuit Rate this link

Building microphone

Boundary-layer dish microphone - ideas for a directional microphone assembly Rate this link
Build a Microphone plug - You only need a 3.5 mm plug (mono) and a very small microphone which is soldered directly onto the contacts of the plug and fits in its housing to build this small microphone for Zaurus palmtop computer. Rate this link
Build These Noise-Canceling Headphones - plus Binaural Microphone Headset, Audio Probe, and Parabolic Microphone Rate this link
Computer Microphone - adapting electret microphone to soundcards with dynamic microphone inputs Rate this link
DAT-Heads Digest #195 - many electret microphone wiring tips Rate this link
DIY microphone for Sony MD R35 minidisc recorder - simple electret microphone Rate this link
Electret MIC Apps - an electret MIC is the best value for money omnidirectional microphone you can buy for 90% of microphone application Rate this link
Electret microphone connection - how to connect electret microphone Rate this link
Electret microphone powering circuits Rate this link
Homemade Binaural Mics Rate this link
Inductive pickup - simple device for detecting audio-frequency electromagnetic signals, such as those emanating from a loudspeaker, or it's cable Rate this link
Interfacing Microphones to Computer Sound Cards Rate this link
JT-MB-D Passive Stereo Matrix for M-S Mic Technique Rate this link
JT-MB-C Used to "Phantom" Power the Realistic PZM Mic Rate this link
Making a rugged, connectorized microphone from a Panasonic microphone capsule Rate this link
Microphone uses phantom power - Phantom-powered microphones derive power for their active circuitry from the receiving-end circuit through the same leads that transmit the audio signal. This design uses this "phantom power" for the electret microphone capsule and a small preamplifier fitted inside microphone. Rate this link
Modification of Panasonic backelectret capacitor microphone (WM-GOAT - DigiKey P9967-ND) - This drawing describes the conventional hookup and option where FET is connected as slource follower with 3 wires to preamp. Rate this link
PAiA MS Microphone Rate this link
Radio Shack Pressure Zone Microphone (PZM) Modifications - This articel gives instructionf for better power supply circuit and also other ideas. Rate this link
Sony C-37A Condenser Microphone - information with circuit diagram Rate this link
Speaker Microphone - circuit that allows you to use a cheap loudspeaker as a poor microphone Rate this link
Telefunken (Neumann) U47 FET Retrofit - replacing amplifier tube with FET Rate this link
To use a Speaker as a Mike - Using this circuit will give a reasonable output signal to drive an amplifier. The Speaker can be any size or even two in series. Rate this link
How to make a binaural stealth mic with an old pair of headphone