2 Watt Amplifier #2:  (diagram added 6/03)

3 Band Equalizer:  (schematic / circuit design added 9/02)

3 Level Audio Power Indicator:  Battery-operated Three LED display that connect it to loudspeaker output   (added 6/06)

3 Tone Gong:  Suitable for use as a door bell (added 6/06)

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 (added 6/06)

300 Watt Subwoofer Power Amplifier:  (electronic circuit added 7/03)

Active Subwoofer and Controller:  (electronic circuit added 7/03)

Active Tone Controls:  (circuit added 10/06)

AN543: Tone Generation:  Microchip Application Note Published 26-Aug-97   (app note added 2/06)

Audio Graphic Equalizer:  simple 7 band equalizer (added 4/02)

Audio Level Indicator #2:  (circuit added 9/04)

Audio Level Indicator:  Audio Amplifier output relay delay (added 6/06)

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 is regulated and programmable, eliminating  need for current limiting resistors. The IC contains an adjustable voltage reference and an accurate ten-step voltage divider. The high-impedance input buffer accepts signals down to ground and up to within 1.5V of  positive supply. Furr, it needs no protection against inputs of ±35V. The input buffer drives 10 individual comparators referenced to  precision divider. Accuracy is typically better than 1 dB.  (added 9/06)

Audio Level Meter:  (diagram added 6/03)

Audio Tone Control:  (circuit added 7/02)

Automatic Loudness Control:  Simple add-on module Switchable "Control-flat" option  (added 3/05)

Automatic Volume Control:  (circuit added 10/06)

Bass-Treble Tone Control Circuit:  The LM1036 is a DC controlled tone (bass/treble), volume and balance circuit for stereo applications in car radio, TV and audio systems. An additional control input allows loudness compensation to be simply effected. Four control inputs provide control of  bass, treble, balance and volume functions through application of DC voltages from a remote control system or, alternatively, from four potentiometers which may be biased from a Zener regulated supply provided on  circuit. Each tone response is defined by a single capacitor chosen to give  desired characteristic.….. (added 6/06)

Better Volume Control:  how to create a log pot that is better than  "real" thing (added 4/02)

Build a Simple Soft Action Muting Switch:  10/14/04   EDN-Design Ideas / (added 10/05)  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....

Designing with the LMC835 Digital Controlled Graphic Equalizer:  National Semiconductor Application Note 04-Nov-1995 (app note added 4/02)

Digital Delay Unit for Surround Sound:  (schematic / circuit design added 9/02)

Digital Volume Control has Log Taper:  04/11/02 EDN Design Ideas  /  (added 12/04)  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:  based on DS1669 Digital Pot IC (added 5/02)

Dual Channel Digital Volume Control:  (electronic Circuit / Schematic added 10/04)

Easy Parametric and Graphic Eq's Plus Peaks and Notches:  (electronic circuit added 8/02)

Generating Tone using Pdo:  Toshiba 870X Series Application Note  (app note added 2/06)

Guitar Control:  CaStand-alone, 9V battery powered unit .  Three-level input selector, three-band tone control  (added 3/05)