We report on the study of direct amplification of femtosecond pulses in an $80\mathrm{\mu }\mathrm{m}$ core diameter microstructured Yb-doped rod-type fiber amplifier in the nonlinear regime. The system includes a compact single grating compressor for the compensation of the small dispersion in the amplifier. With a $1250\mathrm{line}∕\mathrm{mm}$ (l/mm) grating-based compressor, pulses as short as $49\mathrm{fs}$ with $870\mathrm{nJ}$ pulse energy and $12\mathrm{MW}$ peak power are obtained. Alternatively, the use of a $1740\mathrm{l}∕\mathrm{mm}$ grating allows the production of higher quality pulses of $70\mathrm{fs}$ , $1.25\mathrm{\mu }\mathrm{J}$ pulse energy, and $16\mathrm{MW}$ peak power.