Sallen-Key Filter Calculator

A Sallen-Key filter is a popular active filter topology that uses an op-amp as a voltage follower with two resistors and two capacitors to create second-order filtering. It's also known as a VCVS (Voltage Controlled Voltage Source) filter.

The Q factor determines the sharpness of the filter response at the cutoff frequency. A Q of 0.707 gives a maximally flat Butterworth response, while higher Q values create more peaking near the cutoff frequency.

Start by specifying your desired cutoff frequency and Q factor. The calculator will determine appropriate R and C values. For best performance, keep resistor values between 1kΩ and 100kΩ and use standard capacitor values.

Low-pass filters allow frequencies below the cutoff to pass while attenuating higher frequencies. High-pass filters do the opposite, passing frequencies above the cutoff. The component arrangement differs between the two types.

Yes, you can use different values for the resistors and capacitors. Equal values (R1=R2, C1=C2) simplify the design, but unequal values allow more flexibility in achieving specific Q factors and using standard component values.

Choose an op-amp with sufficient bandwidth (at least 10x your cutoff frequency), low input bias current, and appropriate slew rate. Popular choices include TL072, LM358, or OPA2134 depending on your audio quality requirements.

The accuracy depends on component tolerances and op-amp characteristics. Use 1% resistors and 5% capacitors for better accuracy. The actual cutoff may vary by ±10% due to component tolerances.

Sallen-Key filters offer unity gain without additional components, low sensitivity to op-amp parameters, simple design with few components, and good high-frequency performance. They're ideal for audio applications.