In this letter, we present a Mamyshev oscillator with an output power of 332 mW and a pulse energy of 31 nJ, which is directly amplified in an additional fiber section. By balancing the gain-narrowing effect with self-phase modulation during the amplification, we achieved an average output power of 11 W, corresponding to apulse energyofmore than 1 µJ. The pulse duration can be compressed to sub-50 fs behind the amplification stage.