But the problem with using these components to produce an astable multivibrator circuit is that for transistor based astables, many additional components are required, digital astables can generally only be used in digital circuits, and the use of a 555 timer may not always give us a symmetrical output without additional biasing components. The Op-amp Multivibrator circuit however, can provide us with a good rectangular wave signal with the use of just four components, three resistors and a timing capacitor.