Bass Treble Tone Control Circuit using a Single Transistor

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

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

What is Bass Treble Tone Control Circuit:

It is an electrical circuit where the maximum treble setting shapes the treble response by decreasing all frequencies below 500 Hz while the maximum bass setting amplifies all frequencies below 100 Hz to generate a bass boost.

Circuit Working:

Parts List:

Transistor BC547:

In the circuit this is the primary frequency processing device.

Often used in amplification circuits the BC547 is a general purpose NPN bipolar junction transistor (BJT).

Network of Treble Control:

Treble control is operated with a 100k potentiometer and 1000pF capacitors.

By adjusting this potentiometer the output signals treble response can be changed.

Network for Bass Control:

Bass control is handled through a 250k potentiometer and 0.01uF capacitors.

This potentiometer can be easily adjusted to change the output signals bass tone.

Results:

The circuits output gets directly connected to any power amplifier volume control which is often where tone control can be set up.

Gain:

The gain is nearly equal to unity when the single transistor tone control circuits settings are in the flat position.

Therefore the circuit fails to significantly boost or decrease the signal when the bass and treble settings are both set to their center.

Response to Frequency:

The circuit is made to either cut at 15kHz or enhance by around 15dB at 100Hz based on how the treble and bass knobs are set.

This indicates that the circuit has the ability to increase or decrease particular audio signal frequency ranges.

Formulas:

Below are the formulas for Bass Treble Tone Control Circuit using a Single Transistor:

Bass and treble control tones:

These circuits usually consist of two filter stages: a high pass filter for treble boost/cut and a low pass filter for bass boost/cut.

By altering how each step controls the audio flow using capacitors and resistors one can change the equal focus to low and high frequencies.

Response Filter:

The frequency response of each filter stage is calculated using the formula for a first order RC filter which is as follows:

High Pass Filter (Treble):

f_c = 1 / (2 * π * R * C)

where,

• The treble control fcs cutoff frequency Hz is when the signal power starts to sharply decline.
• A rough estimate of the mathematical constant π (pi) is 3.14159.
• The value of Ω for the filter stage resistor is indicated by R.
• C stands for the filter stages capacitor value F.
• Bass low pass filter: The low pass filter stage uses the same method but in order to target bass frequencies a lower cutoff frequency are used.

Important Details:

These calculations estimate the cutoff frequencies.

The actual response of the filter gets impacted by circuit interactions and component limitations.

The bass and treble controls frequently use potentiometers to modify the resistor values R in the filter stages.

By changing the cutoff frequencies the required frequencies are effectively reduced or increased..

How it is Build:

To build a Bass Treble Tone Control Circuit using a Single Transistor follow the connections steps below:

The BC547 Transistor should be placed:

• Install the BC547 transistor onto the PCB or place it onto the breadboard.
• Calculate the transistors emitter, base and collector pins.

Put the base resistor in place:

• From the BC547s base connect a resistor to a suitable voltage source.
• This resistors value is unknown thus one might need to select a resistor value based on the transistors properties and its particular needs.

The Treble Control Network should be included:

• Connect the 100k potentiometer to the transistors base.
• Join the center pin of the potentiometer to the transistors collector the other end to the base and the other end to ground.
• The 100k potentiometers two ends should be connected to two 1000pF capacitors.

Add the Bass Control Network in:

• The 250k potentiometer should be connected to the transistors base.
• Connect the potentiometers base to one end, ground to the other, and the transistors collector to the middle pin.
• Cross the 250k potentiometers two ends with two 0.01uF capacitors.

Attach the power source:

• Connect the power supplies positive and negative terminals to the proper position on the circuit.
• The voltage levels should be within the BC547 transistors functioning range.

Connect the Output:

• The transistors collector output should be connected to the power amplifiers input or another audio system stage.

Modification:

• Turn on the circuit and check the output with an oscilloscope or a speaker and an audio source.
• To change the bass and treble levels, accordingly use the 100k and 250k potentiometers.

Conclusion:

Remember that specific design goals and the properties of the components one using might require to identify the exact resistor values for the base resistor and any other values not included in the initial design.

Before switching on the circuit one should make sure all connections and component values are correct.

References:

What is Bass and Treble?

Treble (sound)

Bass