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Automatic Level Control -
Tone and Balance Circuits

2 Watt Amplifier (Andy Collinson) - Low distortion Amplifier using discrete components

3 Band Equalizer - Using a single op-amp this easy to make equalizer offers three ranges, low frequency, mid frequency, and high. With component values shown there is approximately +/-20dB of boost or cut at frequencies of 50Hz, 1kHz and 10kHz. Supply voltage may be anything from 6 to 30 Volts. Maximum boost 20dB is only realized with maximum supply voltage.

30 Ddm to +30 Ddm Audio Level Meter - circuit with balanced input and adjustable gain to drive needle type VU meter, uses special amplifier module from Op-Amp Labs

300 Watt Subwoofer Power Amplifier

31 Ddm to +30 Ddm Audio Level Meter - circuit with balanced input and adjustable gain to drive needle type VU meter, uses special amplifier module from Op-Amp Labs

555 Timer MonoStable Circuit using Pushbutton - The two circuits above illustrate using the 555 timer to close a relay for a predetermined amount of time by pressing a momentary N/O push button. The circuit on the left can be used for long time periods where the push button can be pressed and released before the end of the timing period. For shorter periods, a capacitor can be used to isolate the switch.

A Better Volume Control - A volume control using a linear pot that is much better than most log pots

A Stereo Digital Volume Control based on the CS3310 - The CS3310 is a complete stereo digital volume control designed specifically for audio systems. It features a 16-bit serial interface that controls two independent, low distortion audio channels. The CS3310 includes an array of well-matched resistors and a low noise active output stage.

Active Subwoofer & Controller

AN011 Jitter Testing Procedures for Compliance with AT&T 62411

AN012 AT&T 62411 Design Considerations Jitter & Synchronization

AN016 Jitter Attenuation Performance of the CS61575 & CS61575A

AN543: Tone Generation - Microchip Application Note

Audio Graphic Equalizer - simple 7 band equalizer

Sound Level Indicator - Audio Amplifier output relay delay

Audio Level Meter - 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.

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.

Audio Tone Control - designed by Aaron Cake

Audio Tone Controls - Many people at one time or other, regardless of their interest in electronics, have adjusted these controls to suit their preference. Whether its to boost the bass of their favorite CD, cut the noise / static on a talk radio station or compensate for poor loud speaker response, they've reached for the treble and bass tone controls.

Automatic Loudness Control - Simple add-on module Switchable "Control-flat" option

Beetle Mk III - This project is based on our most stable FM transmitter. It has a number of features, with a volume control to adjust the input level and a small, neat box to make it easier to attach to a guitar. The volume control is positioned at the end and when turned up fully, the transmitter provides fuzz (distortion). 

Better Volume Control - how to create a log pot that is better than the "real" thing

Build a Simple Soft Action Muting Switch - 10/14/04 EDN-Design Ideas: The circuit in Figure 1 adds a soft muting switch with power-up/power-down muting to a line-level audio circuit. R4, C1, and JFET Q1 quietly ground a signal in 100 to 200 msec when you close S1 or release it when you open S1. Potentiometer R2, set to twice Q1's cutoff voltage, makes  on/off transition.

Calibrating the Current Offset Bias (COB) Register for the DS278x Family of Fuel Gauges - Maxim App Note 4188

Delay Unit For Surround Sound - The Mitsubishi M65830 Digital Delay IC has been discontinued (for reasons beyond my comprehension), and so far a suitable replacement device has not been found. This means (of course) that you will be unable to build this delay circuit. I have left the project in place as reference, and the overall connection schematic is still valid if (when?) a replacement for the M65830 is located. The project will be updated at that time. In the meantime, just ignore the delay circuit

Designing with the LMC835 Digital Controlled Graphic Equalizer - National Semiconductor Application Note 04-Nov-1995

Digital Delay Unit For Surround Sound - The Mitsubishi M65830 Digital Delay IC has been discontinued (for reasons beyond my comprehension), and so far a suitable replacement device has not been found. This means (of course) that you will be unable to build this delay circuit. I have left the project in place as reference, and the overall connection schematic is still valid if (when?) a replacement for the M65830 is located. The project will be updated at that time. In the meantime, just ignore the delay circuit

Digital volume control (Aaron Cake) - based on DS1669 Digital Pot IC

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

Digital Volume Control has Log Taper - EDN-Design Ideas: Digital potentiometers provide a compact and convenient way to attenuate audio-amplifier signals. However, most such potentiometers suffer from at least one flaw: a nonlogarithmic step increment. To avoid this problem, a user must usually step the potentiometer in a nonlinear sequence to simulate a logarithmic taper.

Digital-Volume Control Circuit - The heart of this digital volume controller DVC circuit is IC2 4067, 16-channel analog multiplexer. Because the 1kΩ has been connected between every input and output, the multiplexer can act like a potentiometer. The total resistance is 15kΩ . You can use different values for the resistor to obtain a different characteristic. The current consumption is 1mA.

Dual Channel Digital Volume Control

Easy Parametric & Graphic Eq's Plus Peaks & Notches

Expandable Graphic Equalizer - The project described in this article is a constant Q, fully expandable graphic equalizer.  Where most "conventional" graphic EQ circuits have a Q that is dependent on the setting of the pot, this one maintains the same Q at all settings. 

Generating Tone using Pdo - Toshiba 870X Series Application Note

Guitar Control - CaStand-alone, 9V battery powered unit .  Three-level input selector, three-band tone control
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