Sallen-Key High-Pass Filter Calculator
Design a 2nd-order Sallen-Key active high-pass filter. Solves R and C values for target cutoff and Q with Butterworth/Bessel/Chebyshev presets.
How to Use
- Enter cutoff frequency and Q (or filter-type preset).
- Enter capacitor value (both caps equal); tool solves for R1 and R2.
- Result: resistor values and achieved cutoff.
Show Work
Formulas (equal-C topology)
History
The Sallen-Key high-pass is the dual of the low-pass — swap R and C positions in the original 1955 Sallen-Key topology. Both versions appeared in the same Lincoln Lab paper that introduced the ladder-op-amp architecture.
Sallen-Key high-pass is widely used as the first stage of AC-coupled amplifiers, subsonic filters for audio (removing turntable rumble and amplifier DC drift before loudspeaker amps), and the HP section of bandpass filter designs. Cascaded HP sections create higher-order Butterworth/Bessel/Chebyshev HP filters.
Modern integrated filters (MAX7480 switched-cap, TI TLV320 audio codec decimators) and fully-digital filtering have reduced the need for discrete Sallen-Key designs, but it remains the simplest breadboard HPF and the first active-filter topology in most textbooks.
About This Calculator
Enter cutoff frequency and Q. Enter capacitor value C (equal caps, C1 = C2). The tool solves R1 and R2 using the Q = ½√(R2/R1) and fc = 1/(2π·C·√(R1·R2)) equations. Round to nearest E24 or E96 standard values for build.
For higher order, cascade 2nd-order sections. For example, 4th-order Butterworth HPF: two Sallen-Key sections with Q = 0.541 and Q = 1.307. Everything runs client-side.
About the Sallen-Key High-Pass Filter Calculator
Meet the Sallen-Key High-Pass Filter Calculator: a free, no-fuss tool for electronics and circuit design with nothing to install and no sign-up. Design a 2nd-order Sallen-Key active high-pass filter. Solves R and C values for target cutoff and Q with Butterworth/Bessel/Chebyshev presets.
How it works
Put each value in its box and read the answer as you go. Because it recalculates live, you can play with the inputs to see how each one moves the result — handy for checking your own working or planning ahead. Everything happens on your device, so it is fast and private.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
LP to HP swap?
Swap positions of R and C in the Sallen-Key topology: capacitors in series, resistors to ground. Same fc formula, same Q equation with R and C swapped.
DC-blocking?
Series caps at input/output ensure DC blocking. For AC-coupled audio in/out, use 10 µF electrolytic in series (cutoff < 1 Hz).
Why HPF?
Remove DC offsets, mains hum below 50/60 Hz, subsonic rumble from speakers, slow drift in sensors. Also the HP stage in a bandpass filter.
How do I use the Sallen-Key High-Pass Filter Calculator?
Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Do I need to install or sign up for anything?
Not at all — it runs in the browser with nothing to install and no account. After it loads once, it even works without an internet connection.
Is my information private?
Yes. Everything happens in your browser. Nothing you type is sent to a server or saved anywhere.
Common Use Cases
Audio Subsonic Rumble
20-30 Hz HPF to kill turntable rumble while preserving bass.
AC-Couple Sensor
0.1 Hz HPF to remove slow drift while keeping AC signal.
Bandpass Front-End
Combine with LPF to create bandpass filter around any center frequency.
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