An active crossover circuit is a key part of audio systems that divides an incoming audio signal into different frequency ranges so they can be amplified and played separately.
This helps make sure that each frequency range goes to the right speaker like a woofer for low sounds and a tweeter for high sounds, which improves the overall sound quality and efficiency.
The LM324 operational amplifier or op-amp is often used in these circuits because it is affordable uses little power and can work with either one or two power supplies.
This article will explain how to design and use an active crossover circuit with the LM324 IC.
Circuit Working:
Parts List:
| Component | Value | Quantity |
|---|---|---|
| Resistors | 22k 1/4 watt | 7 |
| Resistors | 6.2k 1/4 watt | 2 |
| Capacitors | 6.8nF | 3 |
| IC | LM324 | 1 |
This circuit diagram shows a second order active crossover circuit that uses the LM324 chip.
It divides the audio signal into two different frequency ranges:
- High frequency output
- Low frequency output
The circuit takes advantage of several op-amps in the LM324 to separate these frequencies, using resistors and capacitors to set the crossover frequency.
Input Stage:
The audio signal comes into the first op-amp, which acts as a buffer.
This buffer helps to isolate the input source and gets the signal ready for the next steps.
High Frequency Filter:
The second op-amp is set up as a high pass filter with components R3, R5 and C1.
This filter lets higher frequencies pass through while blocking lower ones.
The output from this op-amp gives the filtered high frequency signal.
Low Frequency Filter:
The third op-amp works as a low-pass filter using R6, R8 and C2.
It allows lower frequencies to go through while blocking the higher frequencies.
The output from this op-amp provides the filtered low frequency signal.
Final Amplification:
The fourth op-amp boosts the low frequency signal to make sure it is strong enough before it goes out.
Advantages of the Circuit:
- It has a simple and affordable design.
- It uses just one IC LM324 which means fewer parts are needed.
- You can change the crossover frequency by adjusting the resistor or capacitor values.
- It runs on dual power supplies ±15V, which helps improve sound quality.
Applications:
- Used in audio systems for home theaters and studios.
- Found in loudspeakers and public announcement systems.
- Useful for processing specific frequencies in communication devices.
Formulas and Calculations:
Below mentioned are the formulas for Active Crossover Circuit using IC LM324
High Pass Filter:
The cutoff frequency ƒc for high pass and low pass filters is found by using a specific formula.
ƒc = 1 / 2πRC
where,
- R is the resistance for R5
- C is the capacitance for C1
Calculations:
Resistance R= R5 = 22k
Capacitance C = C1 = 6.8nF
Substituting values into the formula: ƒc=1 / 2π × 22 × 103 × 6.8 × 10−9ƒ_c = 1.06kHz
Low Pass Filter:
Resistance R= R8 = 22k
Capacitance C = C2 = 6.8nF
Substituting values into the formula: ƒc=1 / 2π × 22 × 103 × 6.8 × 10−9ƒ_c = 1.06kHz
The crossover frequency we figured out is about 1.06 kHz, which helps keep the high frequency and low frequency signals in the circuit separated properly.
How to Build
To build a Active Crossover Circuit using IC LM324 follow the below mentioned steps for connections:
- Gather all the components as mentioned in the above circuit diagram.
- Connect pin 4 of the LM324 to +15V DC and pin 11 to -15V DC to set up the dual power supply.
- Connect the audio input signal to the non inverting input of the first op-amp which is pin 3.
- Connect a resistor R1 between the input inverting pin 2
- Connect another resistor R2 between pin 1 the output and pin 2 the inverting input.
- Connect pin 3, 5,10 and 12 of IC LM324 to GND
- Connect a capacitor C1 6.8nF in parallel with a resistor R5 and connect them to the inverting input pin 6.
- The output from this op-amp can be found at pin 7, which is the high frequency output.
- Connect the buffer output pin 1 to the non inverting input pin 9 of the third op-amp using another resistor R7.
- Connect a capacitor C2 6.8nF in parallel with a resistor R8 and connect them to the inverting input pin 10.
- The output from this op-amp is available at pin 8, which goes to the next stage for final processing.
- Finally,
- Connect the low frequency signal from pin 8 to the inverting input pin 13 of the fourth op-amp using a resistor R9.
- Connect capacitor C3 6.8nF and a resistor R7 between the output pin 14 and the inverting input pin 13.
- The low frequency output can be found at pin 14.
Conclusion:
The active crossover circuit that uses the LM324 is a smart and useful way to separate audio signals.
It is easy to build, affordable and can be used in many different audio projects.
By dividing frequencies correctly, it improves sound quality and helps each speaker work better on its own.