Bass Treble Tone Control Circuit using a Single Transistor

This circuit is a basic one transistor bass and treble control circuit using a BC547 transistor.

It is a simple tone control circuit that allows you to adjust, the bass and treble levels in an audio signal.

What is Bass Treble Tone Control Circuit:

It is an electronic circuit in which the maximum bass setting amplifies all frequencies below 100Hz to achieve a bass boost, while the maximum treble setting involves cutting all frequencies below 500Hz to shape the treble response.

Circuit Working:

Parts List:

BC547 Transistor:

• This is the main frequency processing device in the circuit.
• BC547 is a general purpose NPN bipolar junction transistor BJT often used in amplification circuits.

Treble Control Network:

• The 100k potentiometer with 1000pF capacitors is responsible for treble control.
• Adjusting this potentiometer will vary the treble response in the output signal.

Bass Control Network:

• The 250k potentiometer with 0.01uF capacitors is responsible for bass control.
• Adjusting this potentiometer will vary the bass response in the output signal.

Output:

• The output of the circuit can be coupled directly into any power amplifier volume control where the tone control is usually configured.

Gain:

• The gain of this single transistor tone control circuit is close to unity when the controls are adjusted in the flat position.
• This means that when both bass and treble controls are set to their midpoint the circuit doesn’t introduce significant gain or attenuation to the signal.

Frequency Response:

• The circuit is designed to provide approximately 15dB boost at 100Hz or cut at 15kHz depending on how the bass and treble controls are adjusted.
• This indicates that the circuit can enhance or reduce specific frequency ranges in the audio signal.

Formulas:

Control tone in the bass and treble:

Two filter stages usually make up these circuits: a low pass filter for bass boost/cut and a high pass filter for treble boost/cut.

You can change the relative focus on low and high frequencies by adjusting the way each stage manipulates the audio signal using capacitors and resistors.

Response Filter:

The following formula for a first order RC filter can be used to approximate the frequency response of each filter stage:

High Pass Filter (Treble):

f_c = 1 / (2 * π * R * C)

where,

• The cutoff frequency Hz for the treble control, f_c is the point at which the signal power begins to dramatically attenuate.
• The mathematical constant π (pi) has a value of roughly 3.14159.
• R represents the filter stage resistor value Ω.
• The filter stages capacitor value F is represented by C.
• Bass low pass filter: The low pass filter stage follows the same algorithm, but the cutoff frequency f_c selected will be lower to target bass frequencies.

Crucial Information:

The cutoff frequencies are approximated by these formulas.

Interactions and component tolerances within the circuit can affect the filters real response.

Potentiometers are commonly used by the bass and treble controls to adjust the resistor values R in the filter stages.

By doing this, the desired frequencies are efficiently cut or amplified by altering the cutoff frequencies.

How it is Build:

Constructing the described single transistor bass treble control circuit involves the below mentioned steps:

Place the BC547 Transistor:

• Insert the BC547 transistor into the breadboard or solder it onto the PCB.
• Identify the emitter, base, and collector pins of the transistor.

Connect the Base Resistor:

• Connect a resistor from the base of the BC547 to an appropriate voltage source.
• The value of this resistor is not specified, so you may need to choose a resistor value based on your specific requirements and the characteristics of the transistor.

Add the Treble Control Network:

• Connect the 100k potentiometer to the base of the transistor.
• Connect one end of the potentiometer to the base, the other end to the ground, and the center pin to the collector of the transistor.
• Connect two 1000pF capacitors across the two arms of the 100k potentiometer.

Include the Bass Control Network:

• Connect the 250k potentiometer to the base of the transistor.
• Connect one end of the potentiometer to the base, the other end to the ground and the center pin to the collector of the transistor.
• Connect two 0.01uF capacitors across the two arms of the 250k potentiometer.

Connect the Power Supply:

• Connect the positive and negative terminals of the power supply to appropriate points on the circuit.
• Ensure that the voltage levels are within the operating range of the BC547 transistor.

Connect the Output:

• Connect the output from the collector of the transistor to the input of your power amplifier or the next stage in your audio system.

Adjustment:

• Power up the circuit and use an oscilloscope or an audio source and a speaker to test the output.
• Adjust the 100k and 250k potentiometers to control the treble and bass levels, respectively.

Conclusion

Remember, the specific resistor values for the base resistor and any other values not specified in the original description may need to be determined based on your specific design goals and the characteristics of the components you are using.

Always double check your connections and component values before applying power to the circuit.

References

What is Bass and Treble?

Treble (sound)

Bass