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.
Index
Low power (<30W)
High power (>30W)
Professional audio amplifier circuit diagrams
Headphone amplifier accessories
Application notes and datasheets
Tube amplifier related circuits
Mixer circuit parts
Input
Output
Input and output in same circuit
Other circuits
Circuits for helping to interface electronic music instruments to mixing desks.
The function of DI box is to convert an unbalanced, high impedence source, to a
balanced, low impedence source for improved noise immunity and to
avoid degradation from long (more than few meters) cable runs.
The output of the DI box is connected to the balanced microphone
input of the mixing desk. Some DI boxes provide also ground isolation
which helps you to get rid of humming caused by ground loops.
Simple DI box ideas
- Black Box Circuit - a 40dB pad/100:1 attenuator for running spaker output to DI-box, so if you put 100 Watts in you'll get around 275 mVolts out
Transformer isolated DI box designs
Active Di box designs
Signal splitters
Signal isolation boxes
Signal combining
Conversion between professional and consumer equipments
Other related circuits
- 2-wire Remot Microphone Amplifier - uses special amplifier module from Opamp Labs
- 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
- Audio preamplifier circuits - three transistor microphone preamplifiers
- A Vacuum Tube Microphone Preamp / Direct Box Project - from January 1997 EQ Column, includes phantom power supply
- 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
- Balanced Mic Preamp - based on SSM2017 and has option for 48V phantom power
- Balanced Microphone Preamp Project - simple preamplifier with phantom power
- Condenser microphone hookup
- DIY Speaker Testing Microphone Preamp
- Dual Phantom Power Microphone Preamplifier - information and full schematic of a kit available from PAiA Electronics, take also look at the circuit diagram
- ECM Mic Preamplifier - low noise electret microphone preamplifier
- Electric Crayons, Anyone? (A Vacuum Tube Microphone Preamp / Direct Box Project) - published in January97 EQ Column
- IC mic preamp uses Jensen Twin-Servo topology
- Intercom preamp - a convenient way of making an intercom is to use a loudspeaker as a microphone
- Jensen Transformers Application Schematics - includes many microphone preamplifier related circuits
- JT-13K6-C in Simple One IC Stage Mic Preamp - 15KB PDF
- Kondensaattorimikrofonin esivahvistin - simple preamplifier for electret microphone, text in Finnish
- 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
- Low Noise Microphone Preamplifier
- Mic-Pre Pan Pot Circuit
- Microphone preamp - very simple two transistor circuit
- Microphone Preamplifier by Jason M. Neal - suitable for speaker measurements
- Modern Microphone Preamplifiers - A paper originally published in R-E-P Magazine, contains general information but does not contain circuit diagrams
- Mu Stage Tube Mic Pre - microphone preamp based on a Jensen transformer and an Alan Kimmel designed "Mu-mode" gain stage
- PAiA Tube Mic Preamp
- Simple microphone preamplifier - simple one transistor circuit
- Simple Transistor Audio Preamplifier - for electret microphone
- Standard Microphone Preamplifier Input Circuitry - pdf file
- Taos Amp Solid State Mic Preamp - simple transformerless microphone preamp, includes circuit board design
- Vintage Neve Class A Circuit Information - Neve BA283AV Class A Preamaplifier Circuit
Microphone accessories
Filters and effects
S/PDIF
SCMS
DAC
Signal conversion
Equipment modifications
Misc
VU meters
- -30dBm to +30dBm Audio Level Meter - circuit with balanced input and adjustable gain to drive needle type VU meter, uses special amplifier module from Opamp Labs
- Audio LED VU meter - built around discrete components
- Audio Millivoltmeter
- Audio Output Level Meter - This unit is designed for monitoring the audio output level across a loudspeaker when carrying out alignment of radios.
- LED Audio VU Meter - logarithmic scale with 3 dB steps, based in LM3915 IC
- LM3916N bar graph driver - datasheet in pdf format, drives a 10 LED bar graph with VU proportions (3dB/step)
- Peak Reading Audio Level Meter - indicates peak audio response on an analogue meter, similar to a tape recorder recording level meter
- Peak Reading Level Meter Using Indicator Tubes
- Sound Level Meter - one chip replacement for the standard analog meters, based on LM3915 audio level IC
- Stereo VU Meter - A simple, low cost stereo VU meter that uses two LM3915 dot/bar display driver ICs to drive 2 rows of 10 LEDs moving bar display, pdf file
- Three-Level Audio Power Indicator - Battery-operated 3 LED display that connect it to loudspeaker output
- Understanding Peak-Reading Meters - includes one example circuit diagram
- VU And PPM Audio Metering - circuits using analugue needle meters
- VU Meter - 5 led VU meter, in pdf format, includes circuit board, text in Finnish
- VU Meter Amplifier
- VU Stereo Meter - will indicate the volume level of the audio going to your speakers by lighting up LEDs, based on LM3915 IC
Decibel meters
Filters needed in audio mesurements
Testers
Distortion measurements
Other measuring circuits and notes
- A Better Volume Control - use linear potentiometer and one tran resistor to make almost logarithmic response curve
- Amplifier Thermal Protection and Shutdown Circuit
- Amplifier Timer - Turns-off your amplifier when idle for 15 minutes, fed by amplifier tape-output
- Ask the Applications Engineer - a collection of articles from its "Analog Dialog" newsletter in pdf format from Analogue Devices, useful info for people designing aDC and DAC systems
- Audio Auto Shutoff - purpose of this circuit is to automatically turn off any device plugged into its power outlets after a certain period of time of silence
- Class A Amplifier Design
- Determining Output Transformer Impedance - When replacing the audio output transformer on a radio, the replacement should match the impedance of the original as close as possible
- DIY class A amplifier chassis & massive heatsink
- Dual +/- 15 volt power supply - suitabe for powering many opamp circuits
- George Krilov audio schematics page - page is about transistor audio power amplifiers, contains articles about power amplifiers shematics, design, construction and SPICE simulation, page is partially in English and partially in Russian
- Guitar Effects FAQ
- Jensen Transformers Application Schematics - many practical circuit ideas using audio transformers
- JT-115K-E90 "Sync" Conversion for Magna-Tech 69C Repro Amplifier - sync track tape head preamplifier
- Load Sensing Automatic Switch - apply power to the entire audio system by turning on one item, simple circuit
- Loudspeaker Protection and Muting - information and circuits
- Low Noise Audio Input Stage - idea for audio input stage for magnetic pickup or microphone using three transistors from Zetex, design note in pdf format
- Main principles of amplifier wiring - how to wire operational amplifier circuits
- Mixed feedback drive circuits dor audio output transformers - using feedback eliminates transformer distortion and primary resistance
- Mosfet Power Amplifiers - A discussion of the benefits of the lateral Mosfet output devices used in todays High Power audio amplifiers
- NE555 drives a speakes: Pulse Width Modulation Amplifier
- Philips SAA1099 Sound Generator
- Proper Grounding Inside Equipment Avoids Ground Noise Coupling (aka"Pin 1 Problems") - 15KB PD
- Pushing the Limits of Audio Power Amplifiers
- Removing the "DC Thump" from Audio Circuits
- Signal Detecting Auto Power-On Unit - switches on relay when detects sound input
- Sheldon's Audio Designs - audio DACs and tube amplifiers
- Simplest Ever Amplifier Bridging - a design for a simple add-on bridging adapter for stereo power amplifiers
- Simulation Electronique SPICE - some hifi circuits and simulation of them using SPICE, text in French
- Soft-Start Circuit For Power Amps - redusces the current spike large transformers take when switched on
- Subtleties count in wide-dynamic-range analog interfaces - transporting high-dynamic-range analog signals from one piece of equipment to another is not a trivial task, this article gives some help to it
- The ALTMANN "SPLIF" Amplifier Topology - something about how to get some of the feedback out of our HIFI amplifiers
- Thermo-Fan To Keep Your Amp Cool - fan controller which controls fan based on temperature
- Variable Amplifier Impedance - idea of being able to vary the output impedance of a power amplifier
Misc circuits
Here you can find links to some ICs which mightr be useful in audio projects.
A/D and D/A conversion
Audio controlling
Recording and playback
Digital audio transmission
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