Active Audio Tone Control Circuit Design

Posted on Feb 6, 2014

This topic continues from the more general Passive Tone Control circuit, which begins using only passive filters. This circuit follows the previous design, although the component values are different and in an alternate configuration. An audio tone control combines both a Base control and a treble control in the same circuit. This design combines

Active Audio Tone Control Circuit Design
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an operational amplifier, as the active element, with a passive filter section. The design also uses a buffer amplifier between the external input to the circuit [not shown] and the actual tone control. The first part of the circuit, comprising the inverting amplifier, is really nothing more than a buffer. The Operational amplifier is configured as an inverting amplifier, with the input applied to the minus input. However the circuit serves no function in regards to the tone control, unless a buffer is a requirement between the filter and presiding circuit. A 0. 47uF input capacitor [value not shown] is used as a DC block with the value selected to pass audio frequencies. The 5uF capacitor at the output of the Op Amp is also a DC block and is not part of the filter circuit. The passive components with comprise the filter are set up just as the previous circuits are, with a few variations. As noted in the diagram, the top part of the filter functions as the bass control and the bottom part of the filter functions as the treble control. The values used in this design differ from the previous circuit. However the values will always be different from circuit to circuit as the designer selects different upper and lower 3dB points for the filter. As the diagram shows the base portion [ low pass filter ] of the circuit may be adjusted with a 3dB point between 32Hz and 320Hz. While the 3dB of the treble section [ high pass filter ]...

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