Baxandall Bass and Tone Project

Here is a negative feedback Baxandall active bass and treble control circuit that is very simple and cheap to construct and works very well. This is a practical circuit with an active filter design because we make use of the virtual earth at the inverting input of the operational amplifier (op amp) and place the filters within the feedback loop of the operational amplifier. In this project, I began with the formulas, wrote a Javascript calculator program, designed the schematic, and board layout, and finally built it. The layout design is on strip board and simple to follow, making it almost like a DIY kit.

LM324

I decided to settle for the LM324 package mainly because of the price. These are currently available in quantities of 20 for as little as two pounds, thereby making it very affordable to make this circuit. Another advantage of this IC package is that it is a Quad, and therefore you will have additional blocks for any other stages you may require in your project. In this circuit design, I use the additional op amps as input buffers. I like this IC because of the symmetrical layout of the internal blocks and pinouts. This makes it much easier to build on stripboard, where you may need two identical circuits in a symmetrical layout. It also makes it much easier for a hobbyist to build it. This circuit requires a split-rail power supply, and I have included a circuit for this in the following articles for this project.

Circuit Design

I decided to upgrade and improve this circuit to make it even cheaper to build with readily available parts. Consequently, this article has been updated, as my intention is to publish only one best performing and practical circuit that could be of use to others. In this circuit, only two capacitors are used in the Baxandall stage, whilst the resistors are all the same value, hence it will be cheaper to get resistors in bulk. In addition I am using 100-kΩ potentiometers which too are cheap and readily available. High-value ganged potentiometers are usually expensive to procure, and therefore this circuit goes a long way to make it affordable for you. Consequently this build may be of use to educational establishments.

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