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dave cox · 25th Nov 2020, 5:51 pm

Your scope may be struggling to trigger properly on the low output ranges. Try connecting the 'sync' output to the scope 'trigger in' if you haven't already.

Wien bridge circuits do take quite a while to stabilize, its not unusual to take a few seconds when you change frequency for the amplitude to settle. The 'gain control' feedback loop needs to have a long time constant to keep the distortion low so the settling will look 'under damped'*.

dc

* 'under-damped', 'critically damped' and 'over-damped' refer to control theory - critical meaning there is (only just) no overshoot! If it take longer then that then it is over (damped) and if it bounces around then its under (damped).

25th Nov 2020, 5:51 pm	#2
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,062	Re: Farnell LF1 oscillator Your scope may be struggling to trigger properly on the low output ranges. Try connecting the 'sync' output to the scope 'trigger in' if you haven't already. Wien bridge circuits do take quite a while to stabilize, its not unusual to take a few seconds when you change frequency for the amplitude to settle. The 'gain control' feedback loop needs to have a long time constant to keep the distortion low so the settling will look 'under damped'. dc 'under-damped', 'critically damped' and 'over-damped' refer to control theory - critical meaning there is (only just) no overshoot! If it take longer then that then it is over (damped) and if it bounces around then its under (damped).