There is then a straight feed-forward path via the 'feedback' resistor to the inoperative output. That mechanism explains the 10K load resistors from the outputs of the first two stages of the op-amp to earth. With this, the feed-forward effect is not noticeable and the clamping resistors are not required. The LM3900 circuit which you will note, does not show an output integrator. The fourth stage compares the rectified tacho generator voltage with the demand speed, integrates the difference and gives an output to drive the PWM modulator.
Motors are mechanical things and take time to react.
But if there is too much gain, then also a feedback oscillator results. Page last updated 7th July, 2001. Page design by Richard Torrens.