Audio Tone Control

An audio tone control combines both a Base control and a treble control in the same circuit. Tone controls are found on lower-end audio gear because it saves both front panel space on the unit and only requires one control knob, instead of two separate controls. In this case potentiometers R2 and R6 are coupled within the same potentiometer case,
Audio Tone Control - schematic

so adjusting one also adjusts the other [one knob, but having separate resistive wipers [ Rotary Wafer Definition ]. The tone control to the right just uses a simple RC filter network, with the capacitor connected in parallel with the variable resistor. The tone control circuit directly below uses a three position switch to select a different capacitor to change the tone of the signal, and is only slightly more complicated than just using a resistor trimmer. The circuit could be made with even fewer parts by only using one capacitor and a switch that connects it to the circuit or removes the capacitor, saving two capacitors. Although the circuit to the right is not a Tone control, it is related to a Tone circuit. A Tone control would only consist of a single control or knob, but the circuit shown uses three separate variable resistors. However what is not depicted in the graphic is that those resistors could be ganged into a single package, basically producing a tone control. The circuit is not a true tone control, but serves to show another circuit, or filter style used to control different frequency ranges. This design uses an LM301 operational amplifier to control the circuit. The passive portion of the tone control is almost identical to the first circuit shown at the top of the page. However there is an additional 10k resistor added between the potentiometer and the Op Amp. Note also that resistor R3 and capacitor C4...

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