Triangle And Square Waveform Generator

V2 output is TTL compatible
R2 adjusts to symmetry of the triangle waveform
Frequency is adjusted with R5 and C

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Microphone Amplifier

This circuit operates from a 1.5 Vdc source.

Low-Impedance Microphone Preamp

This amplifier uses a common-gate FET amplifier to match a low-Z microphone.

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General-Purpose Preamp

This amplifier is useful for audio and video applications. Gain is set by Rf and the voltage gain of this amplifier is approximately 1+Rf/560, where Rf is in ohms. Bandwidth depends on gain selected, but typically it is several MHz. Rf=5.1 kW, which produces a gain of 10*(20dB) voltage.

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Audio Volume Limiter

IC1-a is connected as an inverting amplifier whose gain is controlled by the LDR portion of an optocoupler.

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Audio Distribution Amplifier

Three low-Z audio outputs are available from this circuit, using a quad TL084 FET amplifier. The input is high impedance. Vcc can be 6 to 12 V for typical applications.

Audio Amplifier with Tuneable Filter

This audio amplifier can tune from 500 to 1500Hz and will drive a speaker or headphones. Useful for CW reception or other receiver applications, only two IC devices are needed.

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Subwoofer Crossover Amplifier

    The electronic-crossover circuit contains a summing amplifier that combines the left and right channels from a stereo's headphone jack. Originally used in a subwoofer system, the above circuit might be useful in similar audio applications.

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Subwoofer Amplifier

Designed to feed a low-frequency subwoofer speaker system, the amplifier is capable of up to 100W into an 8-W load. The OPA541BM op amp requires heatsinking and is manufactured by Burr-Brown Corporation. A damping control and relay to eliminate turn-on and turn-off thump in the speaker is included.

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Phono Amplifier with Commom Mode Volume and Tone Control

Noninverting Amplifier using Single Supply

LM380 Personal Stereo Amplifier

With the simple circuit, you can use your personal stereo to drive standard 8 ohm speakers.

Bridge Audio Power Amplifier

1 - 3.5W Bridge Amplifier

This circuit is for low voltage applications requiring high power outputs. Output power levels of 1.0 W into 4 ohm from 6 V and 3.5 V into 8 ohm from 12 V are typical. Coupling capacitors are not necessary since the output dc levels will be
within a few tenths of a volt of each other. Where critical matching is required the 500K potentiometer is added and adjusted for zero dc current flow through the load.

33W Bridge Composite Amplifier

Two LM1875 ICs provide 33W of audio. IC4 is used as a phase inverter.

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Note: IC6 and IC2 must be heatsinked.

12W Low-Distortion Power Amplifier

10W Power Amplifier

Circuit diagram :

 Frequency response:

Two Channel Panning Circuit

This panning circuit (short for panoramic control circuit) provides the ability to move the apparent position of one microphones input between two output channels. This effect is often required in recording studio mixing consoles. 
Panning is how recording engineers manage to pick up you favorite pianist and float the sound over to the other side of the stage and back again.

Sound Mixer/Amplifier

Both input signals can be independently controlled by VR1 and VR2. The balance control VR3 is used to fade out one signal while simultaneously fading in the other. The transistor provides gain and the combined output signal level is controlled by VR4.

The Electronic Crossover Circuit

An audio source, such as a mixer, preamplifier, equalizer, or recorder, is fed to the Electronic Crossover Circuit’s input. That signal is either ac- or dc-coupled, depending on the setting of switch S1, the non- inverting input of buffer-amplifier U1a, one section of quad, BIFET, low-noise TL074 op amp made by Texas Instruments. That stage has a gain of 2, and its output is distributed to both a low-pass filter made by R4, R5, C2, C3, and op-amp U1d, and a highpass filter made by R6, R7, C4, C5, and op amp U1c. Those are 12dB/octave Butterworth-type filters. The Butterworth filter response was chosen because it gives the best compromise between damping and phase shift. Values of capacitors and resistors will vary with the selected crossover at which your unit will operate. The filter's output are fed to a balancing network made by R8, R9, R10, R11 and balance potentiometer R14. When the potentiometer is at its mid-position, there is a unity gain for passbands of both the high and low filters. 

 DC power for the Electronic Crossover Circuit is regulated by R12, R13, D1 and D2. and decoupled by C6 and C7

Low-Distortion Amplifier/Compressor

Designers can build a 15-dB compressor with a miniature lamp and a current-feedback amplifier. The circuit possesses extremely low distortion at frequencies above lamp's thermal time constant. This means that distortion is negligible from audio frequencies to beyond 10 MHz. There's also relatively little change in phase versus gain compared to other automatic gain-control circuits. Lastly, the circuit has many instrumentation, audio, and high-frequency applications as a result of its low distortion and small phase change.

The AD844 op amp is a perfect fit for this application because it's a current-feedback amplifier. Each stage of the circuit. U2. lamp, and feedback resistor compresses an ac signal by over 15dB (see the figure). Cascading a number of stages delivers higher compression ranges.

Op amp U1 operates as a unity-gain buffer to drive the input to the compressor. However. U1 is optional if a low-impedance signal source is used. The lamp's resistance will increase with temperature, which reduces the ration of resistor R3 to the resistance of the lamp. This ratio reduces the gain of U2. The lamp's cold resistance should be greater then the input resistance of U2 (more then 50 ohms) for proper operation. The lamp's resistance will change slightly for low input levels. Therefore, the ratio of R3 to the resistance of the lamp and the gain of U2 stays high.

Audio Fader

In this circuit Q1 is a simple amplifier that has its gain controlled by a variable emitter resistance supplied by FET Q2. In the up position of SI. C3 discharges through R5 and the gain of Q1 decreases because Q2 is driven toward cut-off. In the down position, Q2 conducts more, depending on the setting of R6. which causes a gain increase. By varying R5 or C3, various fade rates can be obtained.