We demonstrate an all-fiber monolithic laser source from a gain-managed nonlinear (GMN) fiber amplifier with a CFBG-based pre-compressor that generates high-contrast pulses with a repetition rate of 80 MHz, average power of 1.6 W, and pulse duration of sub-50 fs. The compressed pulse quality can be optimized by tuning the parameters of the seed pulses injected into the GMN amplifier by controlling the pump power of the fiber pre-amplifier. This compact and cost-effective laser system is a simplified design of the GMN amplification-based femtosecond fiber laser systems. With alignment-free characteristics in the amplifiers and clean compressed pulses, it is easy to assemble and use in applications such as multi-photon microscopy.