I have been tried to investigate and fix this problem by myself. I however cannot find the solution. Please give me some advises.
I used 3 traditional oscillator circuits with opamps (Wien bridge, phase-shift, and twin-T circuits). All of them work correctly when I measure with oscilloscope. I get the sinusoidal waves and can adjust their frequencies and gains. Everything is fine.
The problem is when I use spectrum analyzer (Rigol DS815). After the probe touches the circuit, my sinusoid is ruined (The harmonics rise up). I saw the change in oscilloscope at the same time too. Sometimes the signal disappears and I have to adjust gain to take it back.
In wien bridge, I varied frequencies from 500Hz to 300kHz and Tested with UA741, TL082. Still cannot work it out.
I am thinking that the problem is not about the oscillators, but how I use spectrum analyzer to probe it since the oscilloscope works fine.