We report on experiments performed with a cladding-pumped single-mode Er:Yb-codoped single-frequency fiber amplifier simultaneously seeded by a distributed-feedback diode at 1556nm and a tunable external-cavity diode laser emitting at a wavelength of about 1μm wavelength. The influence of the output wavelength of the external-cavity laser on amplification and reabsorption behavior of the Yb emission as well as the amplifier performance at a wavelength of 1556nm is examined experimentally.