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.

    Phono preamplifiers

    A phono preamplifer is a device which converts the electricalsignal from phono player to a line level signal.The output of a record player is muchlower (few mV) than a line-output signal, and needs to befrequency-corrected (RIAA-correction) and amplified to makeit usable as other line level signal sources.A typical phono input has an EQ curve (RIAA) sloping over 40dB fromlow to high frequency. It also expects an input of ~3.0 millivolts @1KHz. If your stereo amplifier does not have an input for a record player, you should use a phono preamplifier circuit between your turntable and your amplifier. The output of your turntable follows a gain-bandwidth curve called the RIAA compensation curve. The standard AUX input on your stereo does not. Records will sound very strange without an RIAA preamp.

    Audio controlling circuits

    • A Better Volume Control - how to create a log pot that is better than the "real" thing    Rate this link
    • Audio level control with resistive optocouplers - Controlling the level of an audio signal by means of an applied voltage or current has always been somewhat problematical but often desirable. . This application note deals with voltage or current controlled attenuators using optocouplers, primarily in relatively static situations.    Rate this link
    • Audio switching applications for resistive optocouplers - Electronically switching audio signals can be a more complex matter than it might first appear. Not only are there the obvious problems of interfacing between your control logic which is running off a 5V supply and something that is probably controlling a larger voltage swing, but there are the various imperfections of the switch element to consider, which can degrade your precious audio signal.    Rate this link
    • CMOS IC makes low-cost digital potentiometer - A growing trend in the design of electronic equipment is to replace analog knobs used to increase or reduce a continuous signal (such as volume or brightness) with "up" and "down" keys. However, replacing a low-cost analog potentiometer with a digital potentiometer can be costly. The low-cost circuit presented in this article can eliminate the analog potentiometer in many applications. The circuit is based on a 16-channel CMOS multiplexer/demultiplexer and a string of resistors.    Rate this link
    • Construction of a diy motorized volume control - Construction of a motorized potentiometer using a stepper motor for remote controlling/positioning of a standard audio preamplifier volume potentiometer (or whatever).    Rate this link
    • Convert voltage to potentiometer-wiper setting - This circuit converts an analog input voltage, VIN, to a proportional wiper setting of a DPP (digitally programmable potentiometer). The potentiometer's wiper setting, which varies from position 0 through 31, corresponds to the input voltage, which varies from 0 to 1V dc. Thedigital potentiometer used is CAT5114, a 32-tap potentiometer with an increment/decrement interface.    Rate this link
    • Digitally control gain over a ?40-dB range - digitally control an amplifier's gain over a ?40-dB range gain resolution of 1.25 dB    Rate this link
    • Digital Volume Control - based on DS1669 Digital Pot IC    Rate this link
    • Elektroninrn potentiometri - electronic potentiometer for audio, text in Finnish    Rate this link
    • Fixed Attenuators - Fixed attenuators can be designed to have either equal or unequal impedances and to provide any amount of attenuation (theoretically) equal to or greater than the configuration's minimum attenuation - depending on the ratio of Z1/Z2. Attenuators with equal terminations have a minimum attenuation of 0 dB. Unequal terminations place a lower limit on the attenuation.    Rate this link
    • Gain Control - Applications as disparate as test equipment, audio, medical imaging, and cellular base-station radios need to manage signal amplitudes in the analog domain. This article tells about those applications.    Rate this link
    • Inexpensive relays form digital potentiometer - build a digitally controllable isolated potentiometer which can tolerate voltages up to 60V dc    Rate this link
    • Improve FET-based gain control - One problem with standard FET gain-control circuits is increased noise when you use the FET as a part of a resistive attenuator in series with an op amp. When you substitute the FET for the gain-setting resistor in a noninverting op-amp circuit, distortion limits the circuit configuration to applications in which the input voltage is less than a few hundred millivolts.    Rate this link
    • Linear potentiometer implements logarithmic gain control - Trimmer potentiometers are ubiquitous components and are available in a variety of packages, resolutions, and temperature stabilities but none of these potentiometers implements anything but the usual linear function of resistance vs shaft position as useful in many audio applications. This fact makes trouble for applications that need a wide dynamic-adjustment range. Fortunately, you can use a circuit that approximates a logarithmic gain control using a standard linear-taper potentiometer. By using the wiper as an input terminal, you can use a standard linear-taper potentiometer to implement logarithmic gain control.    Rate this link
    • Nine Ways to Adjust Signal Level - This article describes few different ways to adjust audio signal level.    Rate this link
    • Op amp linearizes attenuator control response - Professional-audio equipment commonly uses Analog Devices' ( high-performance, quad-voltage-controlled SSM2164 attenuator. The control response is -30 dB/V, with 0V producing unity gain. Attenuation increases as the applied control voltage increases in the positive direction. This circuit extends the range of applications for this versatile chip by providing a simple means of linearizing the control response. The result is an amplifier with gain directly proportional to the control voltage.    Rate this link
    • Op amp linearizes response of FET VCA - FETs find common use in VCAs (voltage-controlled amplifiers) and attenuators, in which the FET serves as a variable resistance. A control voltage applied to the gate sets the channel resistance and overall circuit gain. You frequently need to select individual FETs because of wide spreads in FET characteristics. This circuit uses a master-slave servo technique with a matched-FET pair to implement voltage-controlled variable gain. In this circuit the gain increases linearly from -55 to 0 dB as control voltage varies from 0 to 5V.    Rate this link
    • Printer port activates CMOS switches - This cost-effective design provides control for CMOS switches without the need for an external power supply. Analog switches such as those in the MAX4663 are ideal for use in low-distortion applications. They are preferable to electromechanical relays in automatic test equipment or other applications in which you need current switching. The CMOS switches use lower power, consume less board space, and are more reliable than electromechanical relays.    Rate this link
    • Programmable-gain amplifier is low-cost - Numerous programmable-gain amplifiers are available, but a simple solution provides the option of using 256 gain steps with an 8-bit DAC and higher steps with higher bit DACs.    Rate this link
    • Single stage gives logarithmic gain steps - by placing a variable component in the positive feedback loop of an op amp, you can vary the gain of the stage logarithmically with respect to a linear resistance or conductance    Rate this link
    • Single switch controls digital potentiometer - The control of electronic potentiometers in most today's applications comes from controller-generated signals. However, a significant number of applications exist that require adjustments using manual, front-panel controls. This circuit uses one IC, one switch, and 10 discrete components. It implements the interface of a single DPDT, momentary-contact rocker switch to a DPP (digitally programmable potentiometer) that has a three-wire increment/decrement interface.    Rate this link
    • Single switch controls digital potentiometer - This Design Idea is an evolution and simplification of another. As the earlier design also describes, you can activate the DPDT rocker switch, S1, to produce either a "count-up" or a "countdown" effect at the digital potentiometer, CAT5114.    Rate this link
    • Tack a log taper onto a digital potentiometer - idea to convert linear digital potentiometer to a logarithmic digital potentiometer    Rate this link
    • Technical Secrets of the Crossfader - A crossfader is designed to predictably control the outputs of two separate mixer channels based on the relative position of the fader's knob between its endpoints. It's a simple sounding task but there are many different ways the job can be done, electrically and mechanically. This document describes some of the most commonly used ones. Most crossfader circuits are implemented in one of two basic schemes.    Rate this link
    • Variable-gain stage uses voltage-output DAC - A voltage-output DAC normally generates an output voltage that is a fraction of the input-reference voltage. In many designs, however, it is necessary to multiply the input voltage by a programmable gain, or, in other words, to create a variable-gain stage. You can easily implement a variable-gain stage using a low-cost voltage-output DAC and one operational amplifier. This no-buffer design minimizes noise and voltage offset, but you can use buffered DACs, too. An 80C51 ?C controls the DAC using a three-wire-plus-reset interface.    Rate this link
    • VISW 8 x 4 Stereo audio/video router    Rate this link
    • Voice-Over Circuit - swiches automatically from sound source to microphone when enough sound comes in from microphone    Rate this link
    • Voltage controlled amplifier - three different circuits    Rate this link
    • Voltage Controlled Audio Panner - variable gain amplifier circuit    Rate this link
    • MOSFETs reduce crosstalk effects on analog switches - Some cost-effective analog multiplexer/demultiplexer ICs, such as the CD4053 and CD4066, find frequent use as signal distributors. These digitally controlled analog switches have low on-resistance. However, with all channels in the same package, crosstalk can be annoying and unavoidable. The circuit presented in this article provides a cost-effective and viable method of solving this problem.    Rate this link

    Other related links

    • High-voltage circuits for electrostatic microphones - circuits that can generate the required high-voltage for electrostatic microphones used in bat detectors, circuit can be used to generate a voltage of about 70V using a current of about 4 mA at 6V input voltage    Rate this link
    • Making Cordless Headphones - This project is based on one pair of Realistic voice actuated fm tranceivers Model TRC-500 Cat#21-400 or a similar system.    Rate this link
    • Mains voltage filter and isolator - A good clean voltage source for your stereo does help with the sound quality. This is a simple power line conditioner. There are three outputs. The first output is an isolated one which will be used for noisy products like cd players.The second output is through a low pass filter(20KHZ),for products like turntables. The third is a straight through with no filter,for high current products like amplifiers.    Rate this link


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