Shavano Music Online

    Introduction to Op-Amps - Part 4
    Active Tone Controls

    5/2002 - Jens Moller - http://www.colomar.com/Shavano/intro_opamp4.html
    Please be aware that this discussion is aimed at the Pro-Audio area, and is not intended for Audiophiles or other areas of circuit design outside of the Pro-Audio environment. The concepts are generally the same, if not identical. However the topic area is vast and the intent of this discussion is quick and effective practical usage - not theory, advanced or extremely high end systems.

    Adding an Active Treble/Bass Circuit

    Many people would like to be able to tweek the sound characteristics of a signal that they are amplifying or mixing. There is quite a lot of related math to this, however not that many parts are required to add this functionality. The following circuit requires that there be a pre-amp stage before it and another amplifier stage after it.

    NOTE: The 2 variable resistors should be Audio Taper (Log taper), however Linear taper will work if thats all you have available.

    And it will have a frequency response that matches the following curves:

    Block Diagram of Complete System

    I've used this circuit on PA mixers as well as musical instrument amplifiers. Its not hard to utilize, and it fits in like this:

    Sample Pre-Amp Stage with Trim Control

    NOTE: The Trim Control variable resistor should be Audio Taper (Log taper), however Linear taper will work if thats all you have available.

    Sample 2 channel Mixer Stage

    NOTE: The Level Control (seperate Volume Control) variable resistors should be Audio Taper (Log taper), however Linear taper will work if thats all you have available.

    Questions? Comments? .

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