Noise produced in active filter circuit when resistor values changed, why?

Thread Starter


Joined Jun 12, 2019
For a project, we were asked to design an audio filter circuit using resistors, capacitors and OP177 op-amps only. We created an 8th order circuit with a gain of 2.5 which, while successfully filtering out the higher frequencies seemed to have issues where the volume of the audio at the output was greatly reduced.

To try and counter-act this we increased the gain of the circuit by replacing one of the resistors with a larger value but what happened instead was that when we connected it to power the speaker emitted a large whining noise without an actual audio file being played.

Does anyone have any ideas as to why increasing the value of the resistor could have had such an effect?