Wien Bridge Oscillator Calculator

Max Wien invented the bridge circuit in 1891 at Physikalisches Laboratorium in Würzburg as a precision AC-impedance measurement tool. Wien\'s RC bridge had a unique property: at exactly one frequency, the bridge output phase crosses zero — perfect for a self-sustaining oscillator if you amplify the crossing.

William Hewlett\'s 1939 master\'s thesis at Stanford showed how to convert the Wien bridge into a reliable low-distortion audio oscillator by using an incandescent lamp as an automatic gain-control element. The lamp\'s filament resistance increases as it heats, reducing gain as the signal grows — a perfect negative-feedback AGC that keeps the output a clean sinusoid. Hewlett and David Packard launched their company around this oscillator (HP 200A), selling it to Disney Studios for the 1940 "Fantasia" theatrical sound engineering. HP became a multi-billion-dollar company from that single product.

Modern audio test oscillators use JFETs, PIN diodes, LDRs, or digital-feedback AGCs to achieve THD < 0.0001% — astronomically better than Hewlett\'s lightbulb. But the underlying Wien-bridge topology and its 1/(2πRC) tuning equation are unchanged since 1891.

Enter target frequency and matched resistor R (used in both bridge arms). The tool computes the matched capacitor C = 1/(2πRf) and reports the feedback resistor Rf for gain = 3 (non-inverting op-amp: R_large = 2·Rf, with R_large in the feedback loop).

For reliable oscillation, add an AGC element (small incandescent bulb in series with Rf, or JFET across part of Rf). Without AGC, the amplifier drives into clipping and produces a distorted near-square wave. For tuning, use matched ganged potentiometers to vary R on both arms simultaneously. Everything runs client-side.