I've designed an astable multivibrator for square wave generation using the LM741 op-amp, as showen in the following image:
Now I've played a little with the frequencies it can output. As shown in the image I've got 1kHz both in calculations and in simulation.
If, for example, I needed a frequency of 30kHz I've changed parameters accordingly but my output simulation first of all doesn't get close to the 30khz and it starts to look more triangular than square wave, which it should be.
I've tried adding some Rs=100kΩ at the negative and positive for precautionary reasons, but it didn't do much.