Subwoofer Low Pass Filter Circuit using Op-Amp TL062

A Subwoofer Low Pass Filter Circuit or LPF for short is an important electronic part that allows low frequency signals to pass through while reducing the strength of high frequency signals.

This feature makes it especially useful in audio setups like subwoofers, which are made to deliver deep and powerful bass sounds.

The circuit shown here is an active low pass filter designed for subwoofers using the IC TL062 operational amplifier.

This setup effectively removes high frequency signals ensuring that the bass sound is clear and strong.

The TL062 made by ST Microelectronics has a special design with two high input impedance J-FETs, which means it uses very little power and has a fast response time.

This op-amp is great for audio applications making it perfect for this circuit.

Additionally, the circuit can run on a dual power supply of +12/-12 V DC which helps it work well.

Circuit Working:

Parts List:

The circuit diagram shows the use of operational amplifiers and some passive parts like resistors and capacitors plus the necessary components for power.

The first part acts as an active low pass filter while the second part provides more filtering and boosts the signal.

The input signals left input and right input, go through resistors R1 and R2 and reach the inverting input of operational amplifier which set up to work as an active low pass filter.

The cutoff frequency for this filter is determined by pot VR1 and capacitor C1.

After filtering the output moves to the next stage for more processing.

The second part of operational amplifier configured as an active second order low pass filter.

The final filtering is influenced by pots VR2 and VR3 along with resistors R4 and R5 and capacitors C4 and C5.

The signal that comes out filtered, is sent to the subwoofer amplifier through resistor R7.

The TL062 op-amp works with a dual ±12V power supply.

Also, capacitors C2, C3, C6, and C7 each 0.1µF along with resistors R3 and R6 both at 10Ω help stabilize the power supply and keep the circuit running smoothly.

Below is circuit diagram and circuit working for 12V Dual Power Supply Circuit and how the power is supplied to Subwoofer Low Pass Filter Circuit using Op-Amp TL062

Formulas with Calculations:

Below are the formulas with calculations for Subwoofer Low Pass Filter Circuit using Op-Amp TL062:

The cutoff frequency (Fc) of a low pass filter is given by:

Fc = 1 / (2 * π * R * C)

First Stage Calculation:

here:

• R = 47kΩ (47000Ω)
• C = 39pF (39 × 10⁻¹² F)

Fc = 1 / (2 * 3.1416 * 47000 * 39 × 10⁻¹²)

Fc = 83.6 kHz

Second Stage Calculation:

For the second stage, the cutoff frequency is calculated as:

Fc = 1 / (2 * π * √(VR2 * VR3 * C4 * C5))

here:

• VR1 = 22kΩ (22000Ω)
• VR2 = 22kΩ (22000Ω)
• C4 = 0.47µF (0.47 × 10⁻⁶ F)
• C5 = 0.22µF (0.22 × 10⁻⁶ F)

Fc = 1 / (2 * 3.1416 * √(22000 * 22000 * 0.47 × 10⁻⁶ * 0.22 × 10⁻⁶))

Fc = 100 Hz

The circuit is designed to let frequencies under 100 Hz go through easily, while it reduces the strength of higher frequencies.

This makes it perfect for use with subwoofers.

How to Build:

To build a Subwoofer Low Pass Filter Circuit using Op-Amp TL062 following steps should be followed when designing your own circuit:

• Gather all the components mentioned in the above circuit diagram
• Connect pin 1 of IC1 TL062 to one end of VR1 pot and the other end to pin 2 of IC1 and connect resistor R2 from left input audio.
• Connect capacitor C1 parallel to VR1 pot.
• Connect a resistor R1 from pin 2 of IC1 to right input audio.
• Connect pin 3 of IC1 to GND.
• Connect pin 4 of IC1 to -12V DC through resistor R6 and connect two parallel capacitors C6 and C7 to GND.
• Connect pot VR2 and VR3 center pin to one end of capacitor C4 and other end of capacitor C4 to pin 6 of IC1
• Connect resistor R5 one end from VR3 pot and other end of resistor to capacitor C5 in series to GND.
• Connect pin 5 of IC1 between resistor R5 and capacitor C5
• Connect a resistor R4 one end from pin 1 and other end of R1 to VR2 pot pin
• Connect pin 7 of IC1 to pin 6 of IC1
• Connect a pin 7 to output audio through resistor R7
• Connect pin 8 of IC1 to +12V DC through resistor R3 and connect two parallel capacitors C2 and C3 to GND.

12V Dual Power Supply for the above Circuit:

Working of 12V dual power supply circuit:

The 220V AC mains supply is transformed down to 14-0-14V AC using a center-tapped transformer that can handle 1 ampere of current.

In this setup, the center tap acts as the ground reference.

A bridge rectifier made of four 1N5402 diodes is used to change the alternating voltage into a pulsating direct current DC voltage by rectifying both halves of the AC signal.

During the positive half cycle diodes D1 and D3 do the rectifying while D2 and D4 take over during the negative half-cycle.

To improve the quality of the DC voltage two capacitors each rated at 1000µF and 25V C1 and C2 are added to smooth out the output reducing ripple and providing a more stable output of about +19V and -19V DC before regulation.

The 7812 voltage regulator IC1 is responsible for regulating the positive 12V DC output from the +19V DC, while the 7912 voltage regulator IC2 takes care of the negative 12V DC output from the -19V DC.

These regulators ensure stable outputs of +12V and -12V with very little ripple.

Additionally, two capacitors each with a value of 0.1µF C3 and C4 help filter out high frequency noise making the voltage regulators even more stable.

As a result the IC1 7812 regulator gives +12V DC and the IC2 7912 regulator provides -12V DC, with the ground as the reference point.

This dual power supply setup is great for use in operational amplifier circuits, audio amplifiers, and other circuits that need a ±12V power supply.

Conclusion:

This low-pass filter circuit for a subwoofer is great at getting rid of high frequency noise and boosting the bass sound.

It uses a IC TL062 op-amp which helps keep the sound clear and steady.

You can change the cutoff frequency by adjusting the resistor and capacitor values, so it can be tailored for various audio needs.

References:

Datasheet IC TL062