Tuned band-pass filter based on the Wien bridge.
The RC network formed by two 10 kΩ resistors and two 15 nF capacitors selects a very specific frequency at which the signal has zero phase shift, close to 1 kHz. At this frequency the bridge delivers the signal with a known attenuation, while at lower or higher frequencies it introduces phase shift and attenuation.
The operational amplifier is configured as a non-inverting amplifier. Its gain is set by the resistive feedback network and the potentiometer, allowing the amplification to be adjusted to compensate for the Wien bridge attenuation without causing oscillation.
Thanks to this frequency-selective feedback, only the center frequency is effectively reinforced. Overall, the circuit amplifies a narrow band around 1 kHz and attenuates the rest of the spectrum, behaving as a tuned, adjustable active band-pass filter.
