MFB Band-Pass Filter Designer
R1/R2/R3 for a multiple-feedback band-pass from f₀, Q and gain — the workhorse active band-pass, with the GBW check.
MFB is inverting and tolerant of component spread — its f₀ shifts only with √(R2R3·C1C2), stabler than Sallen-Key at high Q. R2 is the sensitive one (it sets the Q-vs-gain balance): use 1 % parts. The op-amp must supply loop gain at f₀ — the GBW figure shown is the ~20× rule; starve it and the centre frequency sags.
MFB Band-Pass Designer computes the three resistors of a multiple-feedback band-pass from f₀, Q and gain — free, instant and private in your browser. Instrument and tone-detection designers building stable medium-Q bandpasses use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About MFB Band-Pass Filter Designer
MFB Band-Pass Designer computes the three resistors of a multiple-feedback band-pass from f₀, Q and gain using the standard engineering relation: R1 = Q/(ωCG); R2 = Q/(ωC(2Q²−G)); R3 = 2Q/(ωC) — equal-C design. Worked live: 1 kHz, Q = 5, gain 2 with 10 nF caps: R1 ≈ 40 kΩ, R2 ≈ 1.7 kΩ, R3 ≈ 159 kΩ. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use MFB Band-Pass Filter Designer
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use MFB Band-Pass Filter Designer?
- ✓Implements the real formula — R1 = Q/(ωCG) — with the substitution shown, not a black box
- ✓Built for instrument and tone-detection designers building stable medium-Q bandpasses
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate mfb band-pass?+
The three resistors of a multiple-feedback band-pass from f₀, Q and gain follows R1 = Q/(ωCG); R2 = Q/(ωC(2Q²−G)); R3 = 2Q/(ωC) — equal-C design. For example, 1 kHz, Q = 5, gain 2 with 10 nF caps: R1 ≈ 40 kΩ, R2 ≈ 1.7 kΩ, R3 ≈ 159 kΩ. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
Why MFB instead of Sallen-Key for band-pass work?+
MFB's centre frequency depends on component RATIOS more gently, so it detunes far less with tolerance — the practical choice up to Q ≈ 20. Sallen-Key band-passes get touchy above Q ≈ 5. Beyond 20, switch to state-variable/biquad topologies.
What op-amp bandwidth does an MFB band-pass need?+
Loop gain must survive at f₀: budget GBW ≥ 20·G·Q·f₀. A Q = 10, gain-2, 10 kHz filter therefore wants ≥ 4 MHz — a TL072 barely, an NE5532 comfortably. Starved op-amps show as f₀ sagging low and Q drooping.
Is the MFB Band-Pass Designer free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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