Simple tone control design

Here’s a simple tone control design for your home audio system to boost your BASS and treble for more live sound. The circuit is composed of a transistor amplifier to boost the signal because it will be attenuated by the RC filter circuit.

This circuit is very old and is still used by some manufacturers today because of its simplicity and has lesser noise compared to tone control circuit that uses op-amp. This circuit is simulated using simetrix, you can also play on the resistor and capacitor values to suit your needs.

My design can give you as much as 13dB boost on both bass and treble. You can download the simulation file below so that you can play on the  values of the resistors and capacitors.

The disadvantage of this kind of tone control circuit is that the 50% setting will not give you flat response as the simulation result suggest. If you just want to use it for boosting bass and treble then this response will not bother you.

Simulation Result

Circuit improvements

Gain – This circuit provides minimal gain but if you want to increase gain to be able to connect low signal source like mic and guitar, you can lower value of R4 to 100 ohms and parallel a 1uF capacitor to it.

Bass response – for deeper boomy bass sound, you can increase C2 value to 220nF. Take note that bass frequency requires more power. You will notice that if you crank up the bass, your sound system can’t get any louder that it is when the bass is at minimum. This is because the lower frequencies requires higher power to make it heard. To increase the gain of bass, you can lower the value of R3.

Treble response – For more brilliance on the sound, you can decrease C4 to 1nF. For more middle frequencies, you can lower the value of C4.

Transistor selection – Q1 is any multipurpose NPN transistors such as 2N3901, BC549, 2sc1815 to name a few. Remember to adjust the biased resistor to ensure that it will operate in active region, meaning the voltage at collector is half of the supply voltage when at idle condition.

Transistor Biasing

If you want to change the transistor being used, make sure the transistor will still operate in its active region or else you can have distorted sound output. You can confirm it with the simulation, make sure the voltage at the collector should be around half of the VCC or supply voltage. Biasing it near the supply levels will give you distorted signal at some point and will not have maximum dynamic range.

PCB Layout

I have done a quick PCB design for those who want to build this project. Note that I haven’t tested this yet. The layout is only for 1 channel or mono. you can download the files below,

Downloads

Download the simetrix simulation file and PDF file here:

download

 

If you want a stereo tone control with bass, mid and high controls project – click here!

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