Simulation interactive

Croisement classe AB

Le creux que l'on entend à chaque passage par zéro, et le courant de polarisation qui le supprime.

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Each transistor is an emitter follower that only conducts on its own half of the wave: the NPN pushes, the PNP pulls. Pull the bias to 0 V and neither one is on until the input has climbed past its Vbe, so the output sits at zero through a dead band roughly 1.3 V wide — that flat step at every zero crossing is the crossover notch, and the red error trace shows it flipping sign twice per cycle. That is what you hear: a distortion that is worst at low volume, because the notch is a fixed number of volts wide no matter how small the signal is. Bias the two bases about 1.2 V apart and both devices idle at a few tens of milliamps; the handover becomes continuous, the notch closes and THD collapses. Push further and nothing improves — you only burn Pq = 2·Vs·Iq in the heatsink, which is how output stages cook themselves.