Baxandall Bass and Treble Control

Here is a Baxandall active bass and treble control circuit that is very simple to construct. In this active filter design, we make use of the virtual earth at the inverting input of the operational amplifier. Notice how the filter networks are within the feedback loop of the operational amplifier. In this build, the capacitor and potentiometer values dictate the overall design of this circuit, because these components tend to be expensive and difficult to obtain. A great advantage of this circuit is that all the capacitors are 0.068 µF in value. This particular value is readily and cheaply available in metalized film type, and in bulk, which is good for educational establishments. I already had the 100 kΩ potentiometers, which were recycled, hence it saved me some money, however they too are readily available online.

After building this circuit, I had an idea of another Baxandall bass and tone control circuit based on the LM324 IC, and utilising fewer capacitors. It turned out to be cheaper and easier to build, and therefore you should consider reading the Baxandall Project article as well. If you are able to acquire the LM324 IC, then that build is probably a better option as it too works extremely well combined with the RIAA preamplifier circuit. I like that build more because the layout is symmetrical due to the internal organisation of the IC.

Here is my strip board layout that is as simple as I can make it. There is also an enlarged version if you click on its image above.

Components

Additional Components Mod

The circuit also requires two more components between the output and inverting input pins of the op-amp package. You should solder those directly to the pins on the soldering side as a modification. You will need a 1 MΩ resistor and a 39 pF capacitor connected in parallel, and then connected them between the inverting input pin, and the output pin. You should notice the bass and treble response improve. However, before you add these components, compare how well this circuit works without it and then with it.

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